WOOD handbook:

Wood as an engineering material

By Products Laboratory Forest Service U.S. Department of Agriculture

Agriculture Handbook No. 72

Revised August 1974

Library of Congress Catalog Card No. 73—600335 U.S. Forest Products Laboratory 1974. Wood handbook: Wood as an engineering material —(USDA Agr. Handb. 72, rev.) Summarizes information on wood as an engineering material. Properties of wood and wood-base products of particular concern to the architect and engineer are presented, along with discussions of designing with wood and some pertinent uses of wood. KEYWORDS: Wood structure, physical properties (wood), mechanical properties (wood), , , panel products, design, fastenings, wood moisture, drying, gluing, fire resistance, finishing, decay, sandwich construction, preservation, and wood-base products. Oxford 81/85

For sale by the Superintendent of Documents, U.S. Government Office Washington, D.C. 20402. Price $7.85 stock Number 0100^3200

11 PREFACE

Forests, distinct from all their other services Purpose and benefits, supply a basic raw material— wood—which from the earliest times has - This handbook provides engineers, architects, nished mankind with necessities of existence and others with a source of information on the and with comforts and conveniences beyond physical and mechanical properties of wood, number. and how these properties are affected by varia- tions in the wood itself. Practical knowledge One major use has always been in struc- of wood has, over the years, resulted in strong tures, particularly in housing. But despite and beautiful structures, even though exact wood's long service in structures, it has not engineering data were not always available. always been used efficiently. In these days when Continuing research and evaluation techniques the Nation is trying to utilize its resources promise to permit wider and more efficient more fully, better and more efficient use of the utilization of wood and to encourage even more timber crop is vital. advanced industrial, structural, and decora- Authorship tive uses. As an aid to more efficient use of wood as Organization a material of construction, this handbook was Individual chapters describe not only the prepared by the Forest Products Laboratory, wood itself, but wood-based products, and the a unit of the research organization of the principles of how wood is dried, fastened, Forest Service, U.S. Department of Agricul- finished, and preserved from degradation in ture. The Laboratory, established in 1910, is today's world. Each chapter is climaxed with maintained at Madison, Wis., in cooperation a bibliography of allied information. A glos- with the University of Wisconsin. It was the sary of terms is presented at the end of the handbook. first institution in the world to conduct general The problem of adequately presenting infor- research on wood and its utilization. The vast mation for the architect, engineer, and builder accumulation of information that has resulted is complicated by the vast number of spec- from its engineering and allied investigations ies he may encounter in wood form. To prevent of wood and wood products over six decades— confusion, the common and botanical names along with knowledge of everyday construc- for different mentioned in this volume tion practices and problems—is the chief basis conform to the official nomenclature of the for this handbook. Forest Service.

Ill ACKNOWLEDGMENT

The Forest Products Laboratory appreciates the cooperation of other elements of the Forest Service, and representatives of many universi- ties and segments of industry, in preparing this document. The number of such examples of assistance prevent the mentioning of in- dividual contributions, but their assistance is gratefully acknowledged. A special "thank you" is due to the organiza- tions that provided illustrations. These include the Acoustical and Insulating Materials As- sociation, American Association, American Institute of Timber Construction, J. H. Baxter Wood Treating Company, Bell Lumber and Pole Company, Red- wood Association, Forest Products Division of Koppers Co., Inc., National Forest Products Association, and National Particleboard As- sociation.

IV Chapters No. Page 1 Characteristics and Availability of Commercially Important in the United States 1-1 2 Structure of Wood 2-1 3 Physical Properties of Wood 3-1 4 Mechanical Properties of Wood _ _ 4-1 5 Commercial Lumber 5-1 6 Lumber Stress Grades and Allow- able Properties 6-1 7 Fastenings 7-1 8 Wood Structural Members 8-1 9 Gluing of Wood 9-1 10 Glued Structural Members 10-1 11 Plywood 11-1 12 Structural Sandwich Construction 12-1 13 Bent Wood Members 13-1 14 Control of Moisture and Dimen- sional Changes 14-1 15 Fire Resistance of Wood Construc- tion 15-1 16 Painting and Finishing 16-1 17 Protection from Organisms That Degrade Wood 17-1 18 18-1 19 Poles, Piles, and Ties 19-1 20 Thermal Insulation 20-1 21 Wood-Base Fiber and Particle Panel Materials 21-1 22 Modified Woods and -Base Laminates 22-1 Glossary 23-1 Index 24-1

V The use of trade, firm, or corporation names in this publication is for the information and convenience of the reader. Such use does not constitute an official endorsement or approval of any product or service by the U.S. Department of Agriculture to the exclusion of others which may be suitable.

Mention of a chemical in this handbook does not constitute a recommenda- tion; only those chemicals registered by the U.S. Environmental Protection Agency may be recommended, and then only for uses as prescribed in the registration—and in the manner and at the concentration prescribed. The list of registered chemicals varies from time to time; prospective users, therefore, should get current information on registration status from Pesticides Regulation Division, Environmental Protection Agency, Washington, D.C. 20460.

Illustration Requests Requests for copies of illustrations contained in this handbook should be directed to the Forest Products Laboratory, USDA Forest Service, P.O. 5130, Madison, Wis. 53705.

VI FS-351

Chapter 1

CHARACTERISTICS AND AVAILABILITY OF WOODS

COMMERCIALLY IMPORTANT TO THE UNITED STATES

Page Timber Resources and Wood Uses 1-2 and 1-3 Commercial Sources of Wood Products __ 1-4 Use Classes and Trends 1-5 Commercial Species in the United States 1-5 Hardwoods 1-5 Softwoods 1-13 Imported Woods 1-22 Bibliography 1-38

1-1 CHARACTERISTICS AND AVAILABILITY OF WOODS COMMERCIALLY IMPORTANT IN THE UNITED STATES

Through the ages the unique characteristics has diminished as new concepts of wood use and comparative abundance of wood have made have been introduced. Second-growth timber it a natural material for homes and other (fig. 1-1), the balance of the old-growth , structures, , , vehicles, and dec- and imports continue to fill the needs for wood orative objects. Today, for the same reasons, in the quality required. Wood is as valuable wood is prized for a multitude of uses. an engineering material as it ever was, and All wood is composed of , , in many cases technological advances have made ash-forming minerals, and extractives formed it even more useful. in a cellular structure. Variations in the charac- The inherent factors which keep wood in teristics and volume of the four components and the forefront of raw materials are many and differences in cellular structure result in some varied, but one of the chief attributes is its woods being heavy and some light, some stiff availability in many species, sizes, shapes, and and some flexible, some hard and some soft. conditions to suit almost every demand. It has For a single species, the properties are rel- a high ratio of strength to weight and a re- atively constant within limits; therefore, se- markable record for durability and perform- lection of wood by species alone may some- ance as a structural material. Dry wood has times be adequate. However, to use wood to its good insulating properties against heat, best advantage and most effectively in engineer- sound, and electricity. It tends to absorb and ing applications, the effect of specific char- dissipate vibrations under some conditions of acteristics or physical properties must be con- use, yet is an incomparable material for such sidered. musical instruments as violins. Because of Historically, some woods have filled many grain patterns and colors, wood is inherently purposes, while others which were not so readily an esthetically pleasing material, and its ap- available or so desirable qualitatively might pearance may be easily enhanced by stains, serve only one or two needs. The tough, strong, , , and other finishes. It is and durable white , for example, was a easily shaped with tools and fastened with highly prized wood for , bridges, adhesives, nails, , bolts, and . cooperage, barn timbers, farm implements, rail- When wood is damaged it is easily repaired, and road crossties, fenceposts, flooring, paneling, wood structures are easily remodeled or altered. and other products. On the other hand, woods In addition, wood resists oxidation, acid, salt such as black and cherry became primar- water, and other corrosive agents; has a high ily cabinet woods. was manufactured salvage value; has good shock resistance; into tough, hard resilient striking- handles. takes treatments with preservatives and fire Black locust was prized for barn timbers and retardants; and combines with almost any . What the early builder or craftsman other material for both functional and esthetic learned by trial and error became the basis uses. for the decision as to which species to use for a given purpose, and what characteristics TIMBER RESOURCES AND WOOD USES to look for in selecting a tree for a given use. In the United States more than 100 woods It was commonly accepted that wood from are available to the prospective user, but it is gown in certain locations under certain very unlikely that all are available in any one conditions was stronger, more durable, and locality. Commercially, there are about 60 na- more easily worked with tools, or finer grained tive woods of major importance. Another 30 than wood from trees in some other locations. woods are commonly imported in the form of Modern wood quality research has substantiated logs, cants, lumber, and veneer for industrial that location and growth conditions do signif- uses, the building trades, and the craftsman. icantly affect wood properties. A continuing program of timber inventory is The gradual utilization of the virgin forests in effect in the United States through coopera- in the United States has reduced the available tion of Federal agencies and the States. As new supply of large clear logs for lumber and veneer information regarding timber resources be- However, the importance of high quality logs comes available it appears in State and Federal

1-2 M 913 SI4 Figure 1—1.—Reforested area on the Kaniksu Notional Forest in Idaho. Foreground Stocked with western and Douglas-flr reproduced naturally. The central area, edged by mature timber, is a field-planted western white . publications. One of the most valuable source ample, such softwoods as longleaf pine and books is "Timber Trends in the United Douglas- produce wood that is typically har- States," Forest Service, U.S. Department of der than the hardwoods basswood and . Agriculture Forest Resource Report No. 17. Botanically, the softwoods are Gymnosperms, The best source of current information on species that fall into a classification called timber consumption, production, imports, and conifers that have their exposed, usually the demand and price situation is published in cones. Examples are the , , red- periodically in a U.S. Department of Agricul- woods, and . The other broad classi- ture Miscellaneous Publication, entitled "The fication, the Angiosperms, comprise the various Demand and Price Situation for Forest Prod- orders of hardwoods. They have true ucts." Both publications are available from and broad , and the are enclosed the Superintendent of Documents, U.S. Govern- in a . United States softwoods have needle- ment Printing Office, Washington, D.C. 20402. like or scalelike leaves that, except for and baldcypress, remain on the trees through- HARDWOODS AND SOFTWOODS out the year. The hardwoods, with a few excep- tions, lose their leaves in fall or during the Trees are divided into two broad classes, winter. Most of the imported woods, other usually referred to as "hardwoods" and "soft- than those from Canada, are hardwoods. woods." Some softwoods, however, are actually Major resources of species are harder than some of the hardwoods, and some spread across the United States, except for the hardwoods are softer than softwoods. For ex- Great Plains where only small areas are for-

1-3 ested. Species are often loosely grouped in three general producing areas:

Western softwoods Douglas-fir Sitka Ponderosa pine Idaho white pine Western hemlock Sugar pine Western redcedar Lodgepole pine True Port-Orford-cedar Redwood Incense-cedar Engelmann spruce Alaska-cedar Western larch

Northern softwoods Eastern white pine Red pine Jack pine Eastern hemlock Balsam fir Tamarack Eastern spruces Eastern redcedar Northern white-cedar

Southern softwoods Southern pine Eastern redcedar Baldcypress Atlantic white-cedar With some exceptions, most hardwoods oc- cur east of the Great Plains area (fig. 1-2). The following classification is based on the principal producing region for each wood: M I3S 374 Figure 1-3.—Mixed northern liQrdwoods on OHawa National Forest in Michigan. Southern hardwoods COMMERCIAL SOURCES OF WOOD Ash Magnolia Basswood Soft PRODUCTS American Red oak Cottonwood White oak Softwoods are available directly from the Sweetgum , wholesale and retail yards, or lumber Hackberry American sycamore hickory Tupelo brokers. Softwood lumber and plywood are True hickory Black walnut used in construction for forms, scaffolding, American holly Black Black locust , sheathing, flooring, ceiling, trim, Yellow-poplar paneling, cabinets, and many other building Northern and Appalachian hardwoods components. Softwoods may also appear in the form of shingles, sash, doors, and other mill- Ash True hickory Aspen Black locust work, in addition to some rough products such Basswood Hard maple as round treated posts. American beech Soft maple Hardwoods are used in construction for Red oak Black cherry White oak flooring, architectural woodwork, trim, and American ' American sycamore paneling. These items are usually available Cottonwood Black walnut from lumberyards and building supply dealers. Elm Yellow-poplar Hackberry Most lumber and dimension are re- manufactured into furniture, flooring, pallets, Western hardwoods , dunnage, and blocking. Hardwood Red Bigleaf maple lumber and dimension are available directly Oregon ash Paper birch from the manufacturer, through wholesalers Aspen Tanoak and brokers, and in some retail yards. Black cottonwood Both softwood and hardwood forest products ' American chestnut is no longer harvested as a living are distributed throughout the United States, tree, but the lumber is still on the market as "wormy chestnut" and prices are quoted in the Hardwood although they tend to be more readily avail- Market Report. able in or near their area of origin. Local

1-4 preferences and the availability of certain The wood of red alder varies from almost species may influence choice ; but, a wide selec- white to pale pinkish brown and has no visible tion of woods is generally available for building boundary between heartwood and sapwood. construction, industrial uses, remanufacturing, It is moderately light in weight, intermediate and use by home craftsmen. in most strength properties, but low in shock resistance. Red alder has relatively low shrink- USE CLASSES AND TRENDS age. The principal use of red alder is for furni- Some of the many use classifications for wood ture, but it is also used for sash, doors, panel are growing with the overall national economy, stock, and millwork. and others are holding about the same levels of production and consumption. The wood- Ash based industries that are growing most vig- orously convert wood to thin slices (veneer), Important species of ash are white ash particles (chips, flakes, etc.), or fiber pulps {Fraxinus americana), green ash {F, pennsyl- and reassemble the elements to produce ply- vanica), blue ash (F. quadrangulata)y black wood, numerous types of particleboard, paper, ash (F, nigra), pumpkin ash (F. profunda), , and products. Another and Oregon ash (F. latifolia). The first five growing specializes in produc- of these species grow in the eastern half of the ing laminated timbers. Annual production by United States. Oregon ash grows along the the lumber industry has continued for several Pacific coast. years at almost the same board footage. Some Commercial white ash is a group of species of the forest products industries, such as rail- that consists mostly of white ash and green road crossties, cooperage, shingles, and shakes ash, although blue ash is also included. Heart- appear to have leveled off following a period of depressed production, and in some instances wood of commercial white ash is brown; the to be making modest increases in production. sapwood is light colored or nearly white. Second-growth trees have a large proportion of sapwood. Old-growth trees, which character- COMMERCIAL SPECIES IN THE istically have little sapwood, are scarce. UNITED STATES Second-growth commercial white ash is par- The following brief discussions of the princi- ticularly sought because of the inherent quali- pal localities of occurrence, characteristics, and ties of this wood; it is heavy, strong, hard, uses of the main commercial species, or stiff, and has high resistance to shock. Because groups of species, will aid in selecting woods of these qualities such tough ash is used princi- for specific purposes. More detailed informa- pally for handles, oars, vehicle parts, baseball tion on the properties of these and other species bats, and other sporting and athletic goods. is given in various tables throughout this hand- Some handle specifications call for not less than book. five or more than 17 growth rings per inch for Certain uses listed under the individual handles of the best grade. The addition of a species are no longer important. They have weight requirement of 43 or more pounds a been included to provide some information on cubic foot at 12 percent moisture content will the historical and traditional uses of the assure excellent material. species. Oregon ash has somewhat lower strength The common and botanical names given for properties than white ash, but it is used locally the different species conform to the Forest for the same purposes. Service official nomenclature for trees. Black ash is important commercially in the Lake States. The wood of black ash and pump- Hardwoods kin ash runs considerably lighter in weight Alder, Red than that of commercial white ash. Ash trees growing in southern river bottoms, especially Red alder {Alnus rubra) grows along the in areas that are frequently flooded for long Pacific coast between Alaska and California. It periods, produce buttresses that contain rel- is used commercially along the coasts of atively lightweight and weak wood. Such wood Oregon and Washington and is the most abun- is sometimes separated from tough ash when dant commercial hardwood species in these sold. States. Ash wood of lighter weight, including black 1-5 ash, is sold as cabinet ash, and is suitable for The heartwood of basswood is pale yellowish cooperage, furniture, and shipping containers. brown with occasional darker streaks. Bass- Some ash is cut into veneer for furniture, wood has wide, creamy-white or pale brown paneling, wire-bound . sapwood that merges gradually into the heart- wood. When dry, the wood is without odor or Aspen taste. It is soft and light in weight, has fine, "Aspen" is a generally recognized name ap- even texture, and is straight grained and easy plied to bigtooth aspen {Populns grandidentata) to work with tools. Shrinkage in width and and to quaking aspen (P. tremuloides), Aspen thickness during drying is rated as large ; how- does not include balsam poplar (P. balsamifera) ever, basswood seldom warps in use. and the species of Popidtcs that make up the Basswood lumber is used mainly in Venetian group of cottonwoods. In lumber statistics of blinds, sash and door frames, , apiary the U.S. Bureau of the Census, however, the supplies, woodenware, and boxes. Some bass- term "cottonwood" includes all of the preced- wood is cut for veneer, cooperage, excelsior, and ing species. Also, the lumber of and . cottonwood may be mixed in trade and sold either as poplar ('Topple") or cottonwood. The Beech, American name **popple" or "poplar" should not be con- fused with yellow-poplar (Liriodendron tulipi- Only one species of beech, American beech fera), also known in the trade as "poplar." {), is native to the United Aspen lumber is produced principally in the States. It grows in the eastern one-third of the Northeastern and Lake States. There is some United States and adjacent Canadian provinces. production in the Rocky Mountain States. Greatest production of beech lumber is in the The heartwood of aspen is grayish white to Central and Middle Atlantic States. light grayish brown. The sapwood is lighter Beechwood varies in color from nearly white colored and generally merges gradually into sapwood to reddish-brown heartwood in some heartwood without being clearly marked. As- trees. Sometimes there is no clear line of de- pen wood is usually straight grained with a marcation between heartwood and sapwood. fine, uniform texture. It is easily worked. Well- Sapwood may be 3 to 5 inches thick. The wood seasoned aspen lumber does not impart odor has little figure and is of close, uniform texture. or flavor to foodstuffs. It has no characteristic taste or odor. The wood of aspen is lightweight and soft. The wood of beech is classed as heavy, hard, It is low in strength, moderately stiff, moder- strong, high in resistance to shock, and highly ately low in resistance to shock, and has a adaptable for . Beech has large moderately high shrinkage. shrinkage and requires careful drying. It ma- Aspen is cut for lumber, pallets, boxes and chines smoothly, is an excellent wood for turn- crating, pulpwood, particleboard, excelsior, ing, wears well, and is rather easily treated matches, veneer, and miscellaneous turned with preservatives. articles. Largest amounts of beech go into flooring, furniture, brush blocks, handles, veneer wood- Basswood en-ware, containers, cooperage, and laundry American basswood ( americana) is the appliances. When treated, it is suitable for rail- most important of the several native basswood way ties. species; next in importance is white bass- wood (T. heterophylla). Other species occur Birch only in very small quantities. Because of the similarity of the wood of the different species, The important species of birch are yellow no attempt is made to distinguish between birch (Betula alleghaniensis), sweet birch (B. them in lumber form. Other common names lenta) y and paper birch (B. papyrifera). Other of basswood are linden, linn, and beetree. of some commercial importance are Basswood grows in the eastern half of the river birch (JS. nigra), gray birch (ß. populi- United States from the Canadian provinces folia), and western paper birch (ß. papyrifera southward. Most basswood lumber comes from var. commutata). the Lake, Middle Atlantic, and Central Yellow birch, sweet birch, and paper birch States. In commercial usage, "white basswood" grow principally in the Northeastern and Lake is used to specify white wood or sapwood of States. Yellow and sweet birch also grow along either species. the Appalachian Mountains to northern Geo-

1-6 rgia. They are the source of most birch lumber fied by pinkish tones or darker brown streaks. and veneer. The wood is moderately light in weight—about Yellow birch has white sapwood and light the same as eastern white pine—rather coarse- reddish-brown heart wood. Sweet birch has textured, moderately weak in bending and light-colored sapwood and dark brown heart- endwise compression, relatively low in stiffness, wood tinged with red. Wood of yellow birch moderately soft, and moderately high in shock and sweet birch is heavy, hard, strong, and resistance. Butternut machines easily and has good shock-resisting ability. The wood is finishes well. In many ways it resembles black fine and uniform in texture. Paper birch is walnut, but it does not have the strength or lower in weight, softer, and lower in strength hardness. Principal uses are for lumber and than yellow and sweet birch. Birch shrinks con- veneer, which are further manufactured into siderably during drying. furniture, cabinets, paneling, trim, and mis- Yellow and sweet birch lumber and veneer cellaneous rough items. go principally into the manufacture of furni- ture, boxes, baskets, , woodenware, Cherry, Black cooperage, interior finish, and doors. Birch veneer goes into plywood used for flush doors, Black cherry {Prumts serótina) is sometimes furniture, paneling, radio and television cab- known as cherry, wild black cherry, wild cherry, inets, aircraft, and other specialty uses. Paper or chokecherry. It is the only native species birch is used for turned products, including of the of commercial importance spools, bobbins, small handles, and toys. for lumber production. It occurs scatteringly from southeastern Canada throughout the Buckeye eastern half of the United States. Production is centered chiefly in the Middle Atlantic States. Buckeye consists of two species, yellow The heartwood of black cherry varies from buckeye (Aesculios octandra) and Ohio buck- light to dark reddish brown and has a distinc- eye (A. glabra). They range from the Ap- tive luster. The sapwood is narrow in old trees palachians of Pennsylvania, Virginia, and and nearly white. The wood has a fairly uni- North Carolina westward to Kansas, Oklahoma, form texture and very satisfactory machining and Texas. Buckeye is not customarily sepa- properties. It is moderately heavy. Black cherry rated from other species when manufactured is strong, stiff, moderately hard, and has high into lumber and can be utilized for the same shock resistance and moderately large shrink- purposes as aspen, basswood, and yellow- age. After seasoning, it is very dimensionally poplar. stable in use. The white sapwood of buckeye merges Black cherry is used principally for furni- gradually into the creamy or yellowish white ture, fine veneer panels, architectural wood- of the heartwood. The wood is uniform in work, and for backing blocks on which electro- texture, generally straight-grained, light in type plates are mounted. Other uses include weight, weak when used as a beam, soft, and burial caskets, woodenware novelties, patterns, low in shock resistance. It is rated low on and paneling. It has proved satisfactory for machineability such as shaping, mortising, gunstocks, but has a limited market for this steam bending, boring, and turning. purpose. Buckeye is suitable for pulping for paper and in lumber form has been used principally Chestnut, American for furniture, boxes, and crates, food con- tainers, woodenware, novelties, and American chestnut (Castanea dentata) is mill products. known also as sweet chestnut. Before chest- was attacked by a blight, it grew in com- Butternut mercial quantities from New England to northern Georgia. Practically all standing chest- Butternut ( cinérea) is also called nut has been killed by blight, and supplies white walnut, American white walnut, and oil- come from dead timber. There are still quanti- nut. It grows from southern New Brunswick ties of standing dead chestnut in the Appalach- and Maine, west to Minnesota. Its southern ian Mountains, which may be available for some range extends into northeastern Arkansas and time because of the great natural resistance to eastward to western North Carolina. decay of its heartwood. The narrow sapwood is nearly white, and the The heartwood of chestnut is grayish brown heartwood is a light brown, frequently modi- or brown and becomes darker with age. The

1-7 sapwood is very narrow and almost white. The Elm wood is coarse in texture, and the growth rings are made conspicuous by several rows of large, Six species of elm grow in the eastern distinct pores at the beginning of each year's United States: American elm (Ulrmts ameri- growth. Chestnut wood is moderately light cana) ^ slippery elm (Î7. rubra)y rock elm (U. in weight. It is moderately hard, moderately thomasii), winged elm (U, alata), cedar elm low in strength, moderately low in resistance (U. crassifolia), and September elm (Î7. seró- to shock, and low in stiffness. It seasons well tina). American elm is also known as white elm, and is easy to work with tools. water elm, and gray elm; slippery elm as red Chestnut was used for poles, railway ties, elm; rock elm as elm or hickory elm; furniture, caskets, boxes, crates, and core winged elm as wahoo; cedar elm as red elm stock for veneer panels. It appears most fre- or basket elm; and September elm as red quently now as 'Vormy chestnut" for panel- elm. ing, trim, and picture frames, while a small Supply of American elm is threatened by amount is still used in rustic fences. two diseases, Dutch Elm and phloem necrosis, which have killed hundreds of thousands of trees. CoUonwood The sapwood of the is nearly white and the heartwood light brown, often tinged Cottonwood includes several species of the with red. The elms may be divided into two genus , Most important are eastern general classes, hard elm and soft elm, based cottonwood (P. deltoides and varieties), also on the weight and strength of the wood. Hard known as Carolina poplar and whitewood; elm includes rock elm, winged elm, cedar elm, swamp cottonwood (P. heterophylla), also and September elm. American elm and sHp- known as cottonwood, river cottonwood, and pery elm are the soft elms. Soft elm is swamp poplar; and black cottonwood (P. tri- moderately heavy, has high shock resistance, chocarpa) and balsam poplar (P. halsamifera). and is moderately hard and stiff. Hard elm Eastern cottonwood and swamp cottonwood species are somewhat heavier than soft elm. grow throughout the eastern half of the Elm has excellent bending qualities. United States. Greatest production of lumber Production of elm lumber is chiefly in the is in the Southern and Central States. Black Lake, Central and Southern States. cottonwood grows in the West Coast States and Elm lumber is used principally in boxes, in western Montana, northern Idaho, and baskets, crates, and slack ; furniture, western Nevada. Balsam poplar grows from agricultural supplies and implements; caskets Alaska across Canada, and in the northern and burial boxes, and vehicles. For some uses Great Lake states. the hard elms are preferred. Elm veneer is The heartwood of the three cottonwoods is used for furniture, fruit, vegetable, and cheese grayish white to light brown. The sapwood is boxes, baskets, and decorative panels. whitish and merges gradually with the heart- wood. The wood is comparatively uniform in Hackberry texture, and generally straight grained. It is odorless when well seasoned. Hackberry (Celtis occidentalis) and sugar- Eastern cottonwood is moderately low in (C. laevigata) supply the lumber known bending and compressive strength, moderately in the trade as hackberry. Hackberry grows limber, moderately soft, and moderately low in east of the Great Plains from Alabama, Georgia, ability to resist shock. Black cottonwood is Arkansas, and Oklahoma northward, except slightly below eastern cottonwood in most along the Canadian boundary. Sugarberry strength properties. Both eastern and black overlaps the southern part of the range of cottonwood have moderately large shrinkage. hackberry and grows throughout the Southern Some cottonwood is difficult to work with tools and South Atlantic States. because of fuzzy surfaces. Tension wood is The sapwood of both species varies from pale largely responsible for this characteristic. yellow to greenish or grayish yellow. The heart- Cottonwood is used principally for lumber, wood is commonly darker. The wood resembles veneer, pulpwood, excelsior, and fuel. The lum- elm in structure. ber and veneer go largely into boxes, crates, Hackberry lumber is moderately heavy. It baskets, and pallets. is moderately strong in bending, moderately 1-8 weak in compression parallel to the grain, mod- The major use for hickory is for tool han- erately hard to hard, high in shock resistance, dles, which require high shock resistance. It is but low in stiffness. It has moderately large also used for ladder rungs, athletic goods, agri- to large shrinkage but keeps its shape well cultural implements, dowels, gymnasium ap- during seasoning. paratus, poles, and furniture. Most hackberry is cut into lumber, with A considerable quantity of lower grade small amounts going into dimension stock hickory is not suitable, because of knottiness and some into veneer. Most of it is used for or other growth features and low density, for furniture and some for containers. the special uses of high-quality hickory. It appears particularly useful for pallets, block- Hickory, Pecan ing, and similar items. Hickory and chips and some solid wood is used by the Species of the pecan group include bitternut major packing companies to flavor meat by hickory {Garya oordiformis), pecan (C. il- smoking. linoensis), water hickory (C. aquatica), and hickory (C. myristicaeformis). Bit- Holly, American ternut hickory grows throughout the eastern half of the United States. Pecan hickory grows American holly (Ilex opaca) is sometimes from central Texas and Louisiana to Missouri and Indiana. Water hickory grows from Texas called white holly, evergreen holly, and box- to South Carolina. Nutmeg hickory occurs wood. The natural range of holly extends principally in Texas and Louisiana. along the Atlantic coast, gulf coast, and Mis- The wood of pecan hickory resembles that sissippi Valley. of true hickory. It has white or nearly white Both heartwood and sapwood are white, the sapwood, which is relatively wide, and some- heartwood with an ivory cast. The wood has what darker heartwood. The wood is heavy a uniform and compact texture; it is mod- and sometimes has very large shrinkage. erately low in strength when used as a beam Heavy pecan hickory finds use in tool and or column and low in stiffness, but it is heavy implement handles and flooring. The lower and hard, and ranks high in shock resistance. grades are used in pallets. Many higher grade It is readily penetrable to liquids and can be logs are sliced to provide veneer for furniture satisfactorily dyed. It works well, cuts smoothly, and decorative paneling. and is used principally for scientific and mus- ical instruments, furniture inlays, and athletic Hickory, True goods.

True are found throughout most of Honeylocust the eastern half of the United States. The species most important commercially are shag- The wood of honeylocust (Gleditsia trio- (), pignut (C glabra), shell- canthos) possesses many desirable qualities bark (C. ladniosa), and mockernut (C tomen- such as attractive figure and color, hardness, tosa) . and strength, but is little used because of its The greatest commercial production of the scarcity. Although the natural range of - true hickories for all uses is in the Middle locust has been extended by planting, it is Atlantic and Central States. The Southern and found most commonly in the eastern United South Atlantic States produce nearly half of States, except for New England and the South all hickory lumber. Atlantic and Gulf Coastal Plains. The sapwood of hickory is white and usually quite thick, except in old, slowly growing trees. The sapwood is generally wide and yellowish The heartwood is reddish. From the stand- in contrast to the light red to reddish brown point of strength, no distinction should be heartwood. It is very heavy, very hard, strong made between sapwood and heartwood having in bending, stiff, resistant to shock, and is the same weight. durable when in contact with the ground. The wood of true hickory is exceptionally When available, it is restricted primarily to tough, heavy, hard, strong, and shrinks con- local uses, such as posts and lumber for siderably in drying. For some purposes, both general construction. Occasionally it will show rings per inch and weight are limiting factors up with other species in lumber for pallets where strength is important. and crating.

1-9 Locust, Black cucumbertree is similar to that of yellow- poplar, and cucumbertree growing in the Black locust (Robinia pseudoacacia) is some- yellow-poplar range is not separated from that times called yellow locust, white locust, green species on the market. locust, or locust. This species grows from Magnolia lumber is used principally in the Pennsylvania along the Appalachian Moun- manufacture of furniture, boxes, pallets, Vene- tains to northern Georgia. It is also native to tian blinds, sash, doors, veneer, and millwork. a small area in northwestern Arkansas. The greatest production of black locust timber is in Maple Tennessee, Kentucky, West Virginia, and Vir- ginia. Commercial species of maple in the United Locust has narrow, creamy-white sapwood. States include sugar maple (Acer sacchamm), The heartwood, when freshly cut, varies from black maple (A. nigrum), silver maple (A, greenish yellow to dark brown. Black locust is saccharinum), red maple (A, rubrum), box- very heavy, very hard, very high in resistance elder (A. negundo), and bigleaf maple (A. ma- to shock, and ranks very high in strength and crophyllum). Sugar maple is also known as stiffness. It has moderately small shrinkage. hard maple, rock maple, sugar tree, and black The heartwood has high decay resistance. maple ; black maple as hard maple, black sugar Black locust is used extensively for round, maple, and sugar maple ; silver maple as white hewed, or split mine timbers and for fence- maple, river maple, water maple, and swamp posts, poles, railroad ties, stakes, and fuel. An maple; red maple as soft maple, water maple, important product manufactured from black scarlet maple, white maple, and swamp maple ; locust is insulator pins, a use for which the boxelder as ash-leaved maple, three-leaved wood is well adapted because of its strength, maple, and cut-leaved maple; and bigleaf decay resistance, and moderate shrinkage and maple as Oregon maple. swelling. Other uses are for rough construc- Maple lumber comes principally from the tion, crating, ship treenails and mine equip- Middle Atlantic and Lake States, which to- ment. gether account for about two-thirds of the pro- duction. Magnolia The wood of sugar maple and black maple is known as hard maple; that of silver maple, Three species comprise commercial magno- red maple, and boxelder as soft maple. The lia—southern magnolia (Magnolia grandiflo- sapwood of the is commonly white with ra), sweetbay (M. virginianxi), and cucumber- a slight reddish-brown tinge. It is from 3 to tree (M. acuminata). Other names for southern 5 or more inches thick. Heartwood is usually magnolia are evergreen magnolia, magnolia, big light reddish brown, but sometimes is con- laurel, bull bay, and laurel bay. Sweetbay is siderably darker. Hard maple has a fine, uni- sometimes called swamp magnolia, or more of- form texture. It is heavy, strong, stiff, hard, ten simply magnolia. resistant to shock, and has large shrinkage. The natural range of sweetbay extends along Sugar maple is generally straight grained but the Atlantic and gulf coasts from Long Island also occurs as "birdseye," "curley," and "fid- to Texas, and that of southern magnolia from dleback" grain. Soft maple is not so heavy as North Carolina to Texas. Cucumbertree grows hard maple, but has been substituted for hard from the Appalachians to the Ozarks north- maple in the better grades, particularly for ward to Ohio. Louisiana leads in production furniture. of magnolia lumber. Maple is used principally for lumber, veneer, The sapwood of southern magnolia is yel- crossties, and pulpwood. A large proportion is lowish white, and the heartwood is light to manufactured into flooring, furniture, boxes, dark brown with a tinge of yellow or green. pallets, and crates, shoe lasts, handles, wooden- The wood, which has close, uniform texture ware, novelties, spools, and bobbins. and is generally straight grained, closely re- sembles yellow-poplar. It is moderately heavy, Oak (Red Oak Group) moderately low in shrinkage, moderately low in bending and compressive strength, moder- Most red oak lumber and other products ately hard and stiff, and moderately high in come from the Southern States, the southern shock resistance. Sweetbay is reported to be mountain regions, the Atlantic Coastal Plains, much like southern magnolia. The wood of and the Central States. The principal species

1-10 are: Northern red oak (Quercus rubra), scar- the wood impenetrable by liquids, and for this let oak (Q. coccínea), Shumard oak (Q. shu- reason most white are suitable for tight mardii), pin oak (Q. palustris), Nuttall oak cooperage. Chestnut oak lacks tyloses in many (Q. nuttallii), black oak (Q. velutina), south- of its pores. ern red oak (Q. falcata), cherrybark oak (Q. The wood of white oak is heavy, averaging falcata var. pagodaefolia), water oak (Q. somewhat higher in weight than that of the nigra), laurel oak (Q. laurifolia), and willow red oaks. The heartwood has moderately good oak (Q. phellos). decay resistance. The sapwood is nearly white and usually White oaks are used for lumber, railroad 1 to 2 inches thick. The heartwood is brown ties, cooperage, mine timbers, fenceposts, ve- with a tinge of red. Sawed lumber of red oak neer, fuelwood, and many other products. cannot be separated by species on the basis of High-quality white oak is especially sought the characteristics of the wood alone. Red oak for tight cooperage. Live oak is considerably lumber can be separated from white oak by heavier and stronger than the other oaks, and the number of pores in summerwood and be- was formerly used extensively for ship tim- cause, as a rule, it lacks the membranous bers. An important use of white oak is for growth known as tyloses in the pores. The open planking and bent parts of ships and boats, pores of the red oaks make these species un- heartwood often being specified because of its suitable for tight cooperage, unless the bar- decay resistance. It is also used for flooring, rels are lined with sealer or plastic. Quarter- pallets, agricultural implements, railroad cars, sawed lumber of the oaks is distinguished by truck floors, furniture, doors, millwork, and the broad and conspicuous rays, which add to many other items. its attractiveness. Wood of the red oaks is heavy. Rapidly grown second-growth oak is generally harder The range of sassafras (Sassafras albidum) and tougher than finer textured old-growth covers most of the eastern half of the United timber. The red oaks have fairly large shrink- States from southeastern Iowa and eastern age in drying. Texas eastward. The red oaks are largely cut into lumber, The wood of sassafras is easily confused railroad ties, mine timbers, fenceposts, veneer, with black ash, which it resembles in color, pulpwood, and fuelwood. Ties, mine timbers, grain, and texture. The sapwood is light yel- and fenceposts require preservative treatment low and the heartwood varies from dull gray- for satisfactory service. Red oak lumber is re- ish brown to dark brown, sometimes with a manufactured into flooring, furniture, general reddish tinge. The wood has an odor of sas- millwork, boxes, pallets and crates, agricul- safras on freshly cut surfaces. tural implements, caskets, woodenware, and Sassafras is moderately heavy, moderately handles. It is also used in railroad cars and hard, moderately weak in bending and end- boats. wise compression, quite high in shock resist- ance, and quite durable when exposed to Oak (White Oak Group) conditions conducive to decay. It was highly prized by the Indians for dugout canoes, and White oak lumber comes chiefly from the some sassafras lumber is now used for small South, South Atlantic, and Central States, in- boats. Locally, it is used for fence posts and cluding the southern Appalachian area. rails and general millwork, for foundation Principal species are white oak (Quercus posts, and some wooden containers. alba), chestnut oak (Q. prinus), post oak (Q. stellata), overcup oak (Q. lyrata), swamp chest- Sweetgum nut oak (Q. michauxii), bur oak (Q. macro- carpa), chinkapin oak (Q. muehlenbergii), Sweetgum (Liquidambar styraciflua) grows swamp white oak (Q. bicolor), and live oak from southwestern Connecticut westward into (Q. virginiana), Missouri and southward to the gulf. Lumber The heartwood of the white oaks is gener- production is almost entirely from the South- ally grayish brown, and the sapwood, which ern and South Atlantic States. is from 1 to 2 or more inches thick, is nearly The lumber from sweetgum is usually di- white. The pores of the heartwood of white vided into two classes—sap gum, the light- oaks are usually plugged with the membranous colored wood from the sapwood, and red gum, growth known as tyloses. These tend to make the reddish-brown heartwood. 1-11 Sweetgum has interlocked grain, a form of the heartwood, which also ages to dark red- cross grain, and must be carefully dried. The dish brown. The wood is heavy, hard, and interlocked grain causes a ribbon stripe, how- except for compression perpendicular to the ever, that is desirable for interior finish and grain has roughly the same strength prop- furniture. The wood is rated as moderately erties as eastern white oak. Volumetric shrink- heavy and hard. It is moderately strong, mod- age during drying is more than for white oak, erately stiff, and moderately high in shock and it has a tendency to collapse during drying. resistance. It is quite susceptible to decay, but the sap- Sweetgum is used principally for lumber, wood takes preservatives easily. It has straight veneer, plywood, slack cooperage, railroad ties, grain, machines and glues well, and takes fuel, and pulpwood. The lumber goes princi- staining readily. pally into boxes and crates, furniture, radio Because of tanoak's hardness and abrasion and phonograph cabinets, interior trim, and resistance, it is an excellent wood for flooring millwork. Sweetgum veneer and plywood are in homes or commercial buildings. It is also used for boxes, pallets, crates, baskets, and suitable for industrial applications such as interior woodwork. truck flooring. Tanoak treated with preserva- tive has been used for railroad crossties. The Sycamore, American wood has been manufactured into baseball bats with good results. It is also suitable for American sycamore (Platanus occidentalis) veneer, both decorative and industrial, and for is also known as sycamore and sometimes as high-quality furniture. buttonwood, buttonball tree, and planetree. Sycamore grows from Maine to Nebraska, Tupelo southward to Texas, and eastward to Florida. In the production of sycamore lumber, the The túpelo group includes water túpelo Central States rank first. (Nyssa aquatica), also known as túpelo gum, The heartwood of sycamore is reddish swamp túpelo, and gum; blacktupelo (A^. syl- brown; sapwood is lighter in color and from vatica), also known as black gum; and sour 11/2 to 3 inches thick. The wood has a fine gum; swamp túpelo (AT. sylvatica var. biflora), texture and interlocked grain. It shrinks mod- also known as swamp blackgum, blackgum, erately in drying. Sycamore wood is moder- túpelo gum, and sour gum; Ogeechee túpelo ately heavy, moderately hard, moderately stiff, (N. ogeche), also known as sour túpelo, gopher moderately strong, and has good resistance to shock. , túpelo, and Ogeechee plum. Sycamore is used principally for lumber, All except black túpelo grow principally in veneer, railroad ties, slack cooperage, fence- the southeastern United States. Black túpelo posts, and fuel. Sycamore lumber is used for grows in the eastern United States from Maine furniture, boxes (particularly small food con- to Texas and Missouri. About two-thirds of tainers), pallets, flooring, handles, and butch- the production of túpelo lumber is from the er's blocks. Veneer is used for fruit and Southern States. vegetable baskets, and some decorative panels Wood of the different túpelos is quite similar and door skins. in appearance and properties. Heartwood is light brownish gray and merges gradually in- Tanoak to the lighter colored sapwood, which is gen- erally several inches wide. The wood has fine, In recent years tanoak {Lithocarpus densi- uniform texture and interlocked grain. Tupelo floras) has gained some importance commer- wood is rated as moderately heavy. It is mod- cially, primarily in California and Oregon. erately strong, moderately hard and stiff, and It is also known as -oak because at one moderately high in shock resistance. Buttresses time high-grade in commercial quanti- of trees growing in swamps or flooded areas ties was obtained from the bark. This species contain wood that is much lighter in weight is found in southwestern Oregon and south to than that from upper portions of the same Southern California, mostly near the coast but trees. For some uses, as in the of buttres- also in the Sierra Nevadas. sed ash trees, this wood should be separated The sapwood of tanoak is light reddish from the heavier wood to assure material of brown when first cut and turns darker with uniform strength. Because of interlocked grain, age to become almost indistinguishable from túpelo lumber requires care in drying. 1-12 Tupelo is cut principally for lumber, ve- and hickory poplar. Sapwood from yellow- neer, pulpwood, and some railroad ties and poplar is sometimes called white poplar or slack cooperage. Lumber goes into boxes, pal- whitewood. lets, crates, baskets, and furniture. Yellow-poplar grows from Connecticut and New York southward to Florida and westward Walnut, Black to Missouri. The greatest commercial produc- tion of yellow-poplar lumber is in the South. Black walnut () is also known Yellow-poplar sapwood is white and fre- as American black walnut. Its natural range quently several inches thick. The heartwood extends from Vermont to the Great Plains is yellowish brown, sometimes streaked with and southward into Louisiana and Texas. purple, green, black, blue, or red. These colora- About three-quarters of the walnut timber is tions do not affect the physical properties of produced in the Central States. the wood. The wood is generally straight The heartwood of black walnut varies from grained and comparatively uniform in texture. light to dark brown; the sapwood is nearly Old-growth timber is moderately light in white and up to 3 inches wide in open-grown weight and is reported as being moderately trees. Black walnut is normally straight low in bending strength, moderately soft, and grained, easily worked with tools, and stable moderately low in shock resistance. It has in use. It is heavy, hard, strong, stiff, and has moderately large shrinkage when dried from good resistance to shock. Black walnut wood a green condition but is not difficult to season is well suited for natural finishes. and stays in place well after seasoning. The outstanding uses of black walnut are Much of the second-growth yellow-poplar for furniture, architectural woodwork, and is heavier, harder, and stronger than old decorative panels. Other important uses are growth. Selected trees produce wood heavy gunstocks, cabinets, and interior finish. It is enough for gunstocks. Lumber goes mostly in- used either as solid wood or as plywood. to furniture, interior finish, , core stock for plywood, radio cabinets, and musical in- Willow, Black struments, but use for core stock is decreasing as particleboard use increases. Yellow-poplar Black willow (Salix nigra) is the most im- is frequently used for crossbands in plywood. portant of the many that grow in the Boxes, pallets, and crates are made from lower United States. It is the only one to supply grade stock. Yellow-poplar plywood is used for lumber to the market under its own name. finish, furniture, cases, and various Black willow is most heavily produced in other special products. Yellow-poplar is used the Mississippi Valley from Louisiana to south- also for pulpwood, excelsior, and slack-- ern Missouri and Illinois. age staves. The heartwood of black willow is grayish Lumber from the cucumbertree (Magnolia brown or light reddish brown frequently con- acuminata) sometimes may be included in taining darker streaks. The sapwood is whitish shipments of yellow-poplar because of its simi- to creamy yellow. The wood of black willow is larity. uniform in texture, with somewhat interlocked grain. The wood is light in weight. It has ex- Softwoods ceedingly low strength as a beam or post and is moderately soft and moderately high in shock Alaska-Cedar resistance. It has moderately large shrinkage. Willow is cut principally into lumber. Small Alaska-cedar (Chamaecyparis nootkatensis) amounts are used for slack cooperage, veneer, grows in the Pacific coast region of North excelsior, , pulpwood, artificial limbs, America from southeastern Alaska southward and fenceposts. Black willow lumber is remanu- through Washington to southern Oregon. factured principally into boxes, pallets, crates, The heartwood of Alaska-cedar is bright, caskets, and furniture. Willow lumber is suit- clear yellow. The sapwood is narrow, white to able for roof and wall sheathing, subflooring, yellowish, and hardly distinguishable from the and studding. heartwood. The wood is fine textured and gen- erally straight grained. It is moderately heavy, Yellow-Poplar moderately strong and stiff, moderately hard, and moderately high in resistance to shock. Yellow-poplar (Liriodendron tulipifera) is Alaska-cedar shrinks little in drying, is stable also known as poplar, tulip poplar, tulipwood. in use after seasoning, and the heartwood is

1-13 very resistant to decay. The wood has a mild, Douglas-fir unpleasant odor. Alaska-cedar is used for interior finish, Douglas-fir (Pseudotsuga menziesii and var. furniture, small boats, cabinetwork, and novel- glauca) is also known locally as red fir, Douglas ties. spruce, and yellow fir. The range of Douglas-fir extends from the Baldcypress Rocky Mountains to the Pacific coast and from to central British Columbia. The Baldcypress (Taxodium distichum) is com- Douglas-fir production comes from the Coast monly known as cypress, also as southern States of Oregon, Washington, and Cali- cypress, red cypress, yellow cypress, and white fornia and from the Rocky Mountain States. cypress. Commercially, the terms ''tidewater Sapwood of Douglas-fir is narrow in old- red cypress," ''gulf cypress," "red cypress growth trees but may be as much as 3 inches (coast type)," and "yellow cypress (inland wide in second-growth trees of commercial size. type)" are frequently used. Fairly young trees of moderate to rapid About one-half of the cypress lumber comes growth have reddish heartwood and are called from the Southern States and one-fourth from red fir. Very narrow-ringed wood of old trees the South Atlantic States. It is not as readily may be yellowish brown and is known on the available as formerly. market as yellow fir. The sapwood of baldcypress is narrow and The wood of Douglas-fir varies widely in nearly white. The color of the heartwood var- weight and strength. When lumber of high ies widely, ranging from light yellowish brown strength is needed for structural uses, selec- to dark brownish red, brown, or chocolate. tion can be improved by applying the density The wood is moderately heavy, moderately rule. This rule uses percentage of latewood strong, and moderately hard, and the heart- and rate of growth as a basis. wood of old-growth timber is one of our most Douglas-fir is used mostly for building and decay-resistant woods. Shrinkage is moderately construction purposes in the form of lumber, small, but somewhat greater than that of cedar timbers, piling, and plywood. Considerable and less than that of southern pine. quantities go into railroad ties, cooperage Frequently the wood of certain cypress trees stock, mine timbers, poles, and fencing. contains pockets or localized areas that have Douglas-fir lumber is used in the manufacture been attacked by a . Such wood is known of various products, including sash, doors, gen- as pecky cypress. The decay caused by this eral millwork, railroad-car construction, boxes, fungus is arrested when the wood is cut into pallets, and crates. Small amounts are used lumber and dried. Pecky cypress, therefore, is for flooring, furniture, ship and boat construc- durable and useful where water tightness is tion, wood pipe, and tanks. Douglas-fir ply- unnecessary, and appearance is not important wood has found ever-increasing usefulness in or a novel effect is desired. Examples of such construction, furniture, cabinets, and many usage are as paneling in restaurants, stores, other products. and other buildings. Cypress has been used principally for build- Firs, True (Eastern Species) ing construction, especially where resistance to decay is required. It was used for beams, Balsam fir (Abies balsamea) grows prin- posts, and other members in docks, ware- cipally in New England, New York, Pennsyl- houses, factories, bridges, and heavy construc- tion. vania, and the Lake States. Fraser fir (A. fraseri) grows in the Appalachian Mountains It is well suited for siding and porch con- of Virginia, North Carolina, and Tennessee. struction. It is also used for caskets, burial The wood of the true firs, eastern as well boxes, sash, doors, blinds, and general mill- as western species, is creamy white to pale work, including interior trim and paneling. brown. Heartwood and sapwood are generally Other uses are in tanks, vats, ship and boat indistinguishable. The similarity of wood struc- building, refrigerators, railroad-car construc- ture in the true firs makes it impossible to tion, greenhouse construction, cooling towers, distinguish the species by an examination of and stadium seats. It is also used for railroad the wood alone. ties, poles, piling, shingles, cooperage, and Balsam fir is rated as light in weight, low fenceposts. in bending and compressive strength, moder- 1-14 ately limber, soft, and low in resistance to Eastern hemlock is used principally for lum- ber and pulpwood. The lumber is used largely The eastern firs are used mainly for - in building construction for framing, sheath- wood, although there is some lumber produced ing, subñooring, and roof boards, and in the from them, especially in New England and the manufacture of boxes, pallets, and crates. Lake States. Hemiocic, Western Firs, True (Western Species) Western hemlock ( heterophylla) is also known by several other names, including Six commercial species make up the western west coast hemlock, hemlock spruce, western true firs: Subalpine fir (Abies lasiocarpa), hemlock spruce, western hemlock fir, Prince California red fir (A. magnifica), grand fir Albert fir, gray fir, silver fir, and Alaska pine. (A. grandis), noble fir (A. procera), Pacific It grows along the Pacific coast of Oregon and silver fir (A. amabilis), and white fir (A. Washington and in the northern Rocky Moun- concolor). tains, north to Canada and Alaska. The western firs are light in weight, but, A relative, mountain hemlock, T. merten- with the exception of subalpine fir, have some- siana, inhabits mountainous country from cen- what higher strength properties than balsam tral California to Alaska. It is treated as a fir. Shrinkage of the wood is rated from small separate species in assigning lumber proper- to moderately large. ties. The western true firs are largely cut for The heartwood and sapwood of western hem- lumber in Washington, Oregon, California, lock are almost white with a purplish tinge. western Montana, and northern Idaho and The sapwood, which is sometimes lighter^ in marketed as white fir throughout the United color, is generally not more than 1 inch thick. States. Lumber of the western true firs goes The wood contains small, sound, black knots principally into building construction, boxes that are usually tight and stay in place. Dark and crates, planing-mill products, sash, doors, streaks often found in the lumber and caused and general millwork. In house construction by hemlock bark maggots as a rule do not the lumber is used for framing, subflooring, reduce strength. and sheathing. Some western true fir lumber Western hemlock is moderately light in goes into boxes and crates. High-grade lumber weight and moderate in strength. It is mode- from noble fir is used mainly for interior rate in its hardness, stiffness, and shock re- finish, moldings, siding, and sash and door sistance. It has moderately large shrinkage, stock. Some of the best material is suitable about the same as Douglas-fir. Green hemlock for aircraft construction. Other special and lumber contains considerably more water than exacting uses of noble fir are for Venetian Douglas-fir, and requires longer kiln drying blinds and ladder rails. time. Mountain hemlock has approximately the Hemlocl(, Eastern same density as western hemlock but is some- Eastern hemlock (Tsuga canadensis) grows what lower in bending strength and stiffness. from New England to northern Alabama and Western hemlock is used principally for pulpwood, lumber, and plywood. The lumber Georgia, and in the Lake States. Other names goes largely into building material, such as are Canadian hemlock and hemlock spruce. sheathing, siding, subflooring, , studding, The production of hemlock lumber is di- planking, and . Considerable quantities vided fairly evenly between the New England are used in the manufacture of boxes, pallets, States, the Middle Atlantic States, and the crates, and flooring, and smaller amounts for Lake States. refrigerators, furniture, and ladders. The heartwood of eastern hemlock is pale Mountain hemlock serves some of the same brown with a reddish hue. The sapwood is not uses as western hemlock although the quantity distinctly separated from the heartwood but available is much lower. may be lighter in color. The wood is coarse and uneven in texture (old trees tend to have Incense-Cedar considerable shake) ; it is moderately light in weight, moderately hard, moderately low in Incense-cedar (Lihocedrus decurrens) grows strength, moderately limber, and moderately in California and southwestern Oregon, and low in shock resistance. a little in Nevada. Most incense-cedar lumber 1-15 comes from the northern half of California northern white pine, Weymouth pine, and soft and the remainder from southern Oregon pine. Sapwood of incense-cedar is white or cream colored and the heartwood is light brown, About one-half the production of eastern often tmged with red. The wood has a fine, white pine lumber occurs in the New England uniform texture and a spicy odor. Incense- btates, about one-third in the Lake States, and cedar IS light in weight, moderately low in most of the remainder in the Middle Atlantic strength soft, low in shock resistance, and and South Atlantic States. low in stiffness. It has small shrinkage and is The heartwood of eastern white pine is easy to season with little checking or warping light brown, often with a reddish tinge. It turns Incense-cedar is used principally for lumber considerably darker on exposure. The wood has and fenceposts. Nearly all the high-grade lum- comparatively uniform texture, and is straight ber is used for pencils and Venetian blinds grained. It is easily kiln-dried, has small shrink- home IS used for chests and toys. Much of the age, and ranks high in stability. It is also easy mcense-cedar lumber is more or less pecky to work and can be readily glued. that IS, it contains pockets or areas of dis- Eastern white pine is light in weight, mod- erately soft, moderately low in strength, and integrated wood caused by advanced stages low in resistance to shock. of localized decay in the living tree. There is no further development of peck once the lum- Practically all eastern white pine is con- ber IS seasoned. This lumber is used locally for verted into lumber, which is put to a great rough construction where cheapness and decay variety of uses. A large proportion, which is resistance are important. Because of its re- mostly second-growth knotty lumber of the sistance to decay, incense-cedar is well suited lower grades, goes into and packag- tor fenceposts. Other products are railroad ing applications. High-grade lumber goes into ties, poles, and split shingles. patterns for castings. Other important uses are sash, doors, furniture, trim, knotty panel- ing, finish, caskets and burial boxes, shade Larch, Western and map rollers, toys, and dairy and poultry supplies. '' Western larch {Larix occidentalis) grows in western Montana, northern Idaho, northeastern Pine, Jack Oregon, and on the eastern slope of the Cas- cade Mountains in Washington. About two- Jack pine {Pinus banksiana), sometimes thirds of the lumber of this species is produced known as scrub pine, gray pine, or black pine in Idaho and Montana and one-third in Ores-on in the United States, grows naturally in the and Washington. Lake States and in a few scattered areas in The heartwood of western larch is yellowish New England and northern New York. In brown and the sapwood yellowish white The lumber, jack pine is not separated from the sapwood is generally not more than 1 inch other pines with which it grows, including thick. The wood is stiff, moderately strong and red pine and eastern white pine. hard, moderately high in shock resistance, The sapwood of jack pine is nearly white, the and moderately heavy. It has moderately heartwood is light brown to orange. The sap- large shrinkage. The wood is usually straight wood may make up one-half or more of the grained, splits easily, and is subject to ring volume of a tree. The wood has a rather coarse shake. Knots are common but small and tight texture and is somewhat resinous. It is moder- Western larch is used mainly in building ately light in weight, moderately low in bending construction for rough dimension, small tim- strength and compressive strength, moderately bers, planks and boards, and for railroad ties low m shock resistance, and low in stiffness and mine timbers. It is used also for piles It also has moderately small shrinkage. Lum- poles and posts. Some high-grade material is ber from jack pine is generally knotty. manufactured into interior finish, flooring, sash Jack pine is used for pulpwood, box lumber, and doors. pallets, and fuel. Less important uses include railroad ties, mine timber, slack cooperage poles, and posts. Pine, Eastern White Eastern white pine (Pinus strobus) grows Pine, Lodgepole from Maine to northern Georgia and in the Lake States. It is also known as white pine. Lodgepole pine {Pinus contorta), also known as knotty pine, black pine, spruce pine. 1-16 and jack pine, grows in the Rocky Mountain pine, Califorina white pine, bull pine, and and Pacific coast regions as far northward as black jack. Jeffrey pine (P. jeffreyi), which Alaska. The cut of this species comes largely grows in close association with ponderosa pine from the central Rocky Mountain States; in California and Oregon, is usually marketed other producing regions are Idaho, Montana, with ponderosa pine and sold under that name. Oregon, and Washington. Major producing areas are in Oregon, Wash- The heartwood of lodgepole pine varies from ington, and California. Other important pro- light yellow to light yellow-brown. The sap- ducing areas are in Idaho and Montana ; lesser wood is yellow or nearly white. The wood is amounts come from the southern Rocky generally straight grained with narrow growth Mountain region and the Black Hills of South rings. Dakota and Wyoming. The wood is moderately light in weight, Botanically, ponderosa pine belongs to the fairly easy to work, and has moderately large yellow pine group rather than the white pine shrinkage. Lodgepole pine rates as moderately group. A considerable proportion of the wood, low in strength, moderately soft, moderately however, is somewhat similar to the white stiff, and moderately low in shock resistance. pines in appearance and properties. The heart- Lodgepole pine is used for lumber, mine wood is light reddish brown, and the wide timbers, railroad ties, and poles. Less important sapwood is nearly white to pale yellow. uses include posts and fuel. It is being used The wood of the outer portions of ponderosa in increasing amounts for framing, siding, pine of sawtimber size is generally moderately finish, and flooring. light in weight, moderately low in strength, moderately soft, moderately stiff, and moder- Pme, ately low in shock resistance. It is generally Pitch pine (Pinus rígida) grows from Maine straight grained and has moderately small along the mountains to eastern Tennessee and shrinkage. It is quite uniform in texture and northern Georgia. The heartwood is brownish has little tendency to warp and twist. red and resinous; the sapwood is thick and Ponderosa pine is used mainly for lumber and light yellow. The wood of pitch pine is medium to a lesser extent for piles, poles, posts, heavy to heavy, medium strong, medium stiff, mine timbers, veneer, and ties. The clear medium hard, and medium high in shock re- wood goes into sash, doors, blinds, moldings, sistance. Its shrinkage is medium small to paneling, mantels, trim, and built-in cases and medium large. It is used for lumber, fuel, and cabinets. Lower grade lumber is used for boxes pulpwood. Pitch pine lumber is classified as a and crates. Much of the lumber of intermediate "minor species'' along with pond pine and or lower grades goes into sheathing, subfloor- Virginia pine in southern pine grading rules. ing, and roof boards. Knotty ponderosa pine is used for interior finish. A considerable Pine, Pond amount now goes into particleboard and pulp chips. Pond pine (Pintes serótina) grows in the coast region from New Jersey to Florida. It Pine, Red occurs in small groups or singly, mixed with other pines on low flats. The wood is heavy, Red pine {Pinus resinosa) is frequently coarse-grained, and resinous, with dark, called Norway pine. It is occasionally known as orange-colored heartwood and thick, pale yel- hard pine and pitch pine. This species grows low sapwood. At 12 percent moisture content in the New England States, New York, Penn- it weighs about 38 pounds per cubic foot. sylvania, and the Lake States. In the past, Shrinkage is moderately large. The wood is lumber from red pine has been marketed with moderately strong, stiff, medium hard, and white pine without distinction as to species. medium high in shock resistance. It is used The heartwood of red pine varies from pale for general construction, railway ties, posts, red to reddish brown. The sapwood is nearly and poles. As noted for pitch pine, the lumber white with a yellowish tinge, and is generally of this species is graded as a "minor species" from 2 to 4 inches wide. The wood resembles with pitch pine and Virginia pine. the lighter weight wood of southern pine. Late- Pine, Ponderosa wood is distinct in the growth rings. Red pine is moderately heavy, moderately Ponderosa pine {Pinus ponderosa) is known strong and stiff, moderately soft and moder- also as pondosa pine, western soft pine, western ately high in shock resistance. It is generally

1-17 straight grained, not so uniform in texture as yellowish white and heartwood reddish brown. eastern white pine, and somewhat resinous. The sapwood is usually wide in second-growth The wood has moderately large shrinkage but stands. Heartwood begins to form when the is not difficult to dry and stays in place well tree is about 20 years old. In old, slow-growth when seasoned. trees, sapwood may be only 1 to 2 inches in Red pine is used principally for lumber and width. to a lesser extent for piles, poles, cabin logs, Longleaf and slash pine are classed as posts, pulpwood, and fuel. The wood is used heavy, strong, stiff, hard, and moderately high for many of the purposes for which eastern in shock resistance. Shortleaf and loblolly pine white pine is used. It goes mostly into build- are usually somewhat lighter in weight than ing construction, siding, flooring, sash, doors, longleaf. All the southern pines have moder- blinds, general millwork, and boxes, pallets, ately large shrinkage but are stable when prop- and crates. erly seasoned. To obtain heavy, strong wood of the southern Pine, Southern pines for structural purposes, a density rule has been written that specifies certain visual There are a number of species included in characteristics for structural timbers. the group marketed as southern pine lumber. Dense southern pine is used extensively in The most important, and their growth range, construction of factories, warehouses, bridges, are: trestles, and docks in the form of stringers, (1) Longleaf pine (Pinus palustris), which beams, posts, joists, and piles. Lumber of lower grows from eastern North Carolina southward density and strength finds many uses for into Florida and westward into eastern Texas. building material, such as interior finish, (2) Shortleaf pine (P. echinata), which grows sheathing, subflooring, and joists, and for boxes, from southeastern New York and New Jersey pallets, and crates. Southern pine is used also southward to northern Florida and westward for tight and slack cooperage. When used for into eastern Texas and Oklahoma. (3) Loblolly railroad ties, piles, poles, and mine timbers, it pine (P. taeda), which grows from Maryland is usually treated with preservatives. The southward through the Atlantic Coastal Plain manufacture of structural grade plywood from and Piedmont Plateau into Florida and west- southern pine has become a major wood-using ward into eastern Texas. (4) Slash pine (P. industry. elliottii), which grows in Florida and the south- ern parts of South Carolina, Georgia, Alabama, Pine, Spruce Mississippi, and Louisiana east of the Missis- sippi River. Spruce pine {Pinus glabra), also known as Lumber from any one or from any mixture cedar pine, poor pine, Walter pine, and bot- of two or more of these species is classified tom white pine, is found growing most com- as southern pine by the grading standards of monly on low moist lands of the coastal re- the industry. These standards provide also for gions of southeastern South Carolina, Georgia, lumber that is produced from trees of the long- Alabama, Mississippi, and Louisiana, and and slash pine species to be classified as northern and northwestern Florida. longleaf pine if conforming to the growth-ring Heartwood is light brown, and the wide and latewood requirements of such standards. sapwood zone is nearly white. Spruce pine The lumber that is classified as longleaf in the wood is lower in most strength values than domestic trade is known also as pitch pine in the major southern pines. It compares favor- the export trade. Three southern pines—pitch ably with white fir in important bending prop- pine, pond pine, and Virginia pine—are des- erties, in crushing strength perpendicular ignated in published grading rules as "minor and parallel to the grain, and in hardness. It species," to distinguish them from the four is similar to the denser species such as coast principal species. Douglas-fir and loblolly pine in shear parallel Southern pine lumber comes principally to the grain. from the Southern and South Atlantic States. Until recent years the principal uses of States that lead in production are Georgia, spruce pine were locally for lumber, and for Alabama, North Carolina, Arkansas, and pulpwood and fuelwood. The lumber, which Louisiana. is classified as one of the minor southern pine The wood of the various southern pines is species, reportedly was used for sash, doors, and quite similar in appearance. The sapwood is interior finish because of its lower specific

1-18 gravity and less marked distinction between and generally from 1 to 3 inches wide. The earlywood and latewood. In recent years it has wood is straight grained, easy to work, easily qualified for use in plywood. kiln-dried, and stable after seasoning. This species is moderately light in weight, Pine, Sugar moderately low in strength, moderately soft, moderately stiff, moderately low in shock re- Sugar pine {Firms lambertiana) is some- sistance, and has moderately large shrinkage. times called California sugar pine. Most of the Practically all western white pine is sawed sugar pine lumber is produced in California into lumber and used mainly for building con- and the remainder in southwestern Oregon. stuction, matches, boxes, patterns, and mill- The heartwood of sugar pine is buff or light work products, such as sash, frames, doors, brown, sometimes tinged with red. The sap- and blinds. In building construction, boards of wood is creamy white. The wood is straight the lower grades are used for sheathing, knotty grained, fairly uniform in texture, and easy paneling, subflooring, and roof strips. High- to work with tools. It has very small shrinkage, grade material is made into siding of various is readily seasoned without warping or check- kinds, exterior and interior trim, and finish. ing, and stays in place well. This species is It has practically the same uses as eastern white light in weight, moderately low in strength, pine and sugar pine. moderately soft, low in shock resistance, and low in stiffness. Port-Orford-Cedar Sugar pine is used almost entirely for lum- ber products. The largest amounts are used Port-Orford-cedar ( Chamaecyparis lawson- in boxes and crates, sash, doors, frames, iana) is sometimes known as Lawson cypress, blinds, general millwork, building construc- Oregon cedar, and white cedar. It grows tion, and foundry patterns. Like eastern white along the Pacific coast from Coos Bay, Oreg., pine, sugar pine is suitable for use in nearly southward to California. It does not extend every part of a house because of the ease more than 40 miles inland. with which it can be cut, its ability to stay in The heartwood of Port-Orford-cedar is light place, and its good nailing properties. yellow to pale brown in color. Sapwood is thin and hard to distinguish. The wood has Pine, Virginia fine texture, generally straight grain, and a pleasant spicy odor. It is moderately light Virginia pine (Pinus virginiana), known in weight, stiff, moderately strong and hard, also as Jersey pine and scrub pine, grows and moderately resistant to shock. Port- from New Jersey and Virginia throughout Orford-cedar heartwood is highly resistant to the Appalachian region to Georgia and the Ohio decay. The wood shrinks moderately, has Valley. The heartwood is orange and the sap- little tendency to warp, and is stable after wood nearly white and relatively thick. The seasoning. wood is rated as moderately heavy, moderately Some high-grade Port-Orford-cedar is used strong, moderately hard, and moderately stiff in the manufacture of battery separators and and has moderately large shrinkage and high venetian-blind slats. Other uses are - shock resistance. It is used for lumber, rail- proof boxes, archery supplies, sash and door road ties, mine props, pulpwood, and fuel. It construction, stadium seats, flooring, interior is one of three southern pines to be classi- finish, furniture, and boatbuilding. fied as a "minor species" in the grading rules. Redcedar, Eastern

Pine, Western White Eastern redcedar {Juniperus virginiana) grows throughout the eastern half of the Western white pine (Pinus monticola) is United States, except in Maine, Florida, and a also known as Idaho white pine or white pine. narrow strip along the gulf coast, and at About four-fifths of the cut comes from Idaho the higher elevations in the Appalachian (fig. 1-3) with the remainder mostly from Mountain Range. Commercial production is Washington ; small amounts are cut in Montana principally in the southern Appalachian and and Oregon. Cumberland Mountain regions. Another species, Heartwood of western white pine is cream southern redcedar (/. silicicola), grows over colored to light reddish brown and darkens a limited area in the South Atlantic and Gulf on exposure. The sapwood is yellowish white Coastal Plains.

1-19 „ M 41 I SJS figure 7-3.—Western whife pine timber, mostly privately owned, viewed from Elk Butte In Clearwater National Forest in Idaho.

The heartwood of redcedar is bright red or not over 1 inch in width. The wood is generally dull red, and the thin sapwood is nearly white. straight grained and has a uniform but rather The wood is moderately heavy, moderately low coarse texture. It has very small shrinkage. in strength, hard, and high in shock resistance, This species is light in weight, moderately but low in stiffness. It has very small shrink- soft, low in strength when used as a beam or age and stays in place well after seasoning. The posts, and low in shock resistance. Its heart- texture is fine and uniform. Grain is usually wood is very resistant to decay. straight, except where deflected by knots, Western redcedar is used principally for which are numerous. Eastern redcedar heart- shingles, lumber, poles, posts, and piles. The wood is very resistant to decay. lurnber is used for exterior siding, interior The greatest quantity of eastern redcedar is finish, greenhouse construction, ship and boat used for fenceposts. Lumber is manufactured building, boxes and crates, sash, doors, and into chests, wardrobes, and closet lining. Other millwork. uses include flooring, novelties, pencils, scientific instruments, and small boats. Southern red- Redwood cedar is used for the same purposes. Redwood {Sequoia sempervirens) is a very Redcedar, Western large tree growing on the coast of California. Another sequoia, gaint sequoia {Sequoia Western redcedar {Thuja plicata) grows in gigantea), grows in a limited area in the the Pacific Northwest and along the Pacific Sierra Nevada of California, but is used in coast to Alaska. Western redcedar is also very limited quantities. Other names for red- called canoe cedar, giant arborvitae, shingle- wood are coast redwood, California redwood, wood, and Pacific redcedar. Western redcedar and sequoia. Production of redwood lumber is lumber is produced principally in Washington, limited to California, but a nationwide market followed by Oregon, Idaho, and Montana. exists. The heartwood of western redcedar is reddish The heartwood of redwood varies from a or pinkish brown to dull brown and the sapwood light cherry to a dark . The narrow nearly white. The sapwood is narrow, often sapwood is almost white. Typical old-growth 1-20 redwood is moderately light in weight, mod- width and is often difficult to distinguish from erately strong and stiff, and moderately hard. heartwood. The wood has medium to fine The wood is easy to work, generally straight texture and is without characteristic taste or grained, and shrinks and swells comparatively odor. It is generally straight grained. Engel- little. The heartwood has high decay resistance. mann spruce is rated as light in weight. It Most redwood lumber is used for building. is low in strength as a beam or post. It is It is remanufactured extensively into siding, limber, soft, low in shock resistance, and has sash, doors, blinds, finish, casket stock, and moderately small shrinkage. The lumber typi- containers. Because of its durability, it is use- cally contains numerous small knots. ful for cooling towers, tanks, silos, wood- Engelmann spruce is used principally for pipe, and outdoor furniture. It is used in lumber and for mine timbers, railroad ties, and agriculture for buildings and equipment. Its use poles. It is used also in building construction in as timbers and large dimension in bridges and the form of dimension stock, flooring, sheathing, trestles is relatively minor. The wood splits and studding. It has excellent properties for readily and the manufacture of split products, pulp and . such as posts and fence material, is an impor- tant business in the redwood area. Some red- Spruce, Sitka is manufactured for decorative plywood. Sitka spruce (Picea sitchensis) is a tree of large s/ize growing along the northwestern Spruce, Eastern coast of North American from California to Alaska. It is generally known as Sitka spruce, The term '^eastern spruce" includes three although other names may be applied locally, species, red (Picea ruhens), white (P. glauca), such as yellow spruce, tideland spruce, western and black (P. mariana). White spruce and black spruce, silver spruce, and west coast spruce. spruce grow principally in the Lake States and About two-thirds of the production of Sitka New England, and red spruce in New England spruce lumber comes from Washington and one- and the Appalachian Mountains. All three third from Oregon. species have about the same properties, and The heartwood of Sitka spruce is a light in commerce no distinction is made between pinkish brown. The sapwood is creamy white them. The wood dries easily and is stable after and shades gradually into the heartwood; it drying, is moderately light in weight and easily may be 3 to 6 inches wide or even wider in worked, has moderate shrinkage, and is mod- young trees. The wood has a comparatively fine, erately strong, stiff, tough, and hard. The wood uniform texture, generally straight grain, and is light in color, and there is little difference no distinct taste or odor. It is moderately light between the heartwood and sapwood. in weight, moderately low in bending and com- The largest use of eastern spruce is for pressive strength, moderately stiff, moderately pulpwood. It is also used for framing material, soft, and moderately low in resistance to general millwork, boxes and crates, ladder shock. It has moderately small shrinkage. On rails, scaffold planks, and piano sounding the basis of weight, it rates high in strength boards. properties and can be obtained in clear, straight grained pieces. Spruce, Engelmann Sitka spruce is used principally for lumber, pulpwood, and cooperage. Boxes and crates ac- Engelmann spruce (Picea engelmannii) count for a considerable amount of the re- grows at high elevations in the Rocky Mountain manufactured lumber. Other important uses region of the United States. This species is are furniture, planing-mill products, sash, sometimes known by other names, such as doors, blinds, millwork, and boats. Sitka spruce white spruce, mountain spruce, Arizona spruce, has been by far the most important wood for silver spruce, and balsam. About two-thirds of aircraft construction. Other specialty uses are the lumber is produced in the southern Rocky ladder rails and sounding boards for . Mountain States. Most of the remainder comes from the northern Rocky Mountain States Tamarack and Oregon. The heartwood of Engelmann spruce is Tamarack (Larix laricina) is a small- to nearly white with a slight tinge of red. The medium-sized tree with a straight, round, sapwood varies from % inch to 2 inches in slightly tapered trunk. In the United States

1-21 it grows from Maine to Minnesota, with the bulk of the stand in the Lake States. It was IMPORTED WOODS formerly used in considerable quantity for This section does not purport to discuss all lumber, but in recent years production for that of the woods that have been at one time or purpose has been small. another imported into the United States. The heartwood of tamarack is yellowish Only those species at present considered to be brown to russet brown. The sapwood is whitish, of commercial importance are included. The generally less than an inch wide. The wood is same species may be marketed in the United coarse in texture, without odor or taste, and the States under other common names. transition from earlywood to latewood is Text information is necessarily brief, but abrupt. The wood is intermediate in weight when used in conjunction with the shrinkage and in most mechanical properties. and strength tables (ch. 3 and 4), a reasona- Tamarack is used principally for pulpwood, bly good picture may be obtained of a particular lumber, railroad ties, mine timbers, fuel, wood. The bibliography at the end of this fenceposts, and poles. Lumber goes into fram- chapter contains information on many species ing material, tank construction, and boxes, not described here. pallets, and crates. Afrormosia (See Kokrodua)

Almon (See Lauans) White-Cedar, Northern and Atlantic Andiroba Because of the widespread distribution of Two species of white-cedar grow in the andiroba () in tropical eastern part of the United States—northern America, the wood is known under a variety white-cedar (Thuja occidentalis) and Atlantic of names that include cedro macho, carapa, white-cedar (Chamaecyparis thyoides). North- crabwood, and tangare. These names are also ern white-cedar is also known as arborvitae, applied to the related species Carapa nicara- or simply cedar. Atlantic white-cedar is also guensiSy whose properties are generally inferior known as , southern white-cedar, swamp to those of C. guianensis. The heartwood color varies from reddish cedar, and boat cedar. brown to dark reddish brown. The texture Northern white-cedar grows from Maine (size of pores) is like that of mahogany (Swie- along the Appalachian Mountain Range and tenia). The grain is usually interlocked but westward through the northern part of the is rated as easy to work, , and glue. The Lake States. Atlantic white-cedar grows near wood is rated as durable to very durable with the Atlantic coast from Maine to northern respect to decay and insects. Andiroba is Florida and westward along the gulf coast to heavier than mahogany and accordingly is Louisiana. It is strictly a swamp tree. markedly superior in all static bending prop- Production of northern white-cedar lumber erties, compression parallel to the grain, hard- is probably greatest in Maine and the Lake ness, shear, and toughness. States. Commercial production of Atlantic On the basis of its properties, andiroba ap- white-cedar centers in North Carolina and to be suited for such uses as flooring, along the gulf coast. frame construction in the tropics, furniture The heartwood of white-cedar is light brown, and cabinetwork, millwork, and utility and dec- and the sapwood is white or nearly so. The orative veneer and plywood. sapwood is usually thin. The word is light in weight, rather soft and low in strength, and Angélique low in shock resistance. It shrinks little in drying. It is easily worked, holds paint well, Angélique (Dicorynia guianensis), or basra and the heartwood is highly resistant to de- locus, comes from French Guiana and Surinam cay. The two species are used for similar pur- and was previously identified under the name poses, mostly for poles, ties, lumber, posts, and D, paraensis. Because of the variability in decorative fencing. White-cedar lumber is used heartwood color between different trees, two principally where high degree of durability is forms are commonly recognized by producers. needed, as in tanks and boats, and for wooden- Heartwood that is russet colored when freshly ware. cut, and becomes superficially dull brown with

1-22 a purplish cast, is referred to as "gris." Heart- wood is regarded as more resistant than the wood that is more distinctly reddish and fre- lighter forms. quently shows wide bands of purplish color is Within its region of growth, apamate is used called angelique rouge. extensively for furniture, interior trim, doors, The texture is somewhat coarser than that of flooring, , ax handles, and general black walnut. The grain is generally straight construction. The wood veneers well and pro- or slightly interlocked. In strength, angelique duces an attractive paneling. is superior to and white oak, when either green or air dry, in all properties except tension Apitong perpendicular to grain. Angelique is rated as highly resistant to decay, and resistant to Apitong is the most common structural tim- marine borer attack. Machining properties ber of the Philippine Islands. The principal vary and may be due to differences in density, species are apitong (Dipterocarpits grandiflo- moisture content, and silica content. After the rus)y panau (D. ffracilis), and hagakhak (D. wood is thoroughly air dried or kiln dried, it warburgii). All members of the genus are tim- can be worked effectively only with carbide- ber trees, and all are marketed under the name tipped tools. apitong. Other important species of the genus The strength and durability of angelique are marketed as keruing in Ma- make it especially suitable for heavy construc- laysia and , yang in Thailand, and tion, harbor installations, bridges, heavy gurjun in and Burma. planking for pier and platform decking, and The wood is light to dark reddish brown in railroad bridge ties. The wood is particularly color, comparatively coarse to comparatively suitable for ship decking, planking, boat fine textured, straight grained or very nearly frames, and underwater members. It is cur- so, strong, hard, and heavy. The wood is char- rently being used in the United States for acterized l3y the presence of ducts, which pier and dock fenders and flooring. occur in short arcs as seen from end grain surfaces. Although the heartwood is fairly resistant Apamate to decay and insect attack, the wood should be treated with preservatives when it is to be Apamate (Tabebuia rosea) ranges from used in contact with the ground. southern Mexico through Central America to In machining research at the Forest Prod- Venezuela and . The name roble is ucts Laboratory on apitong and the various frequently applied to this species because of species of "Philippine mahogany," apitong some fancied resemblance of the wood to that ranked appreciably above the average in all of oak (Quercus). Another common name for machining operations. for apamate in Belize is mayflower. Apitong is used for heavy-duty purposes as The sapwood becomes a pale brown upon ex- well as for such items as mine guides, truck posure. The heartwood varies through the floors, chutes, flumes, agitators, pallets, and browns, from a golden to a dark brown. Tex- boardwalks. ture is medium, and grain is closely and nar- rowly interlocked. Heartwood is without Avodire distinctive odor or taste. The wood weighs about 38 pounds per cubic foot at 12 percent Avodire (Turraeanthus africanus) has moisture content. rather extensive range from west- Apamate has excellent working properties ward to the and southward to Zaire. in all machine operations. It ñnishes It is a medium-sized tree of the rain forest in attractively in natural color and takes finishes which it forms fairly dense but localized and with good results. discontinuous stands. Apamate averages lighter in weight than the The wood is cream to pale yellow in color average of the American white oaks, but is with a high natural luster and eventually dark- comparable with respect to bending and com- ens to a golden yellow. The grain is sometimes pression parallel to grain. The white oaks are straight but more often is wavy or irregularly superior with respect to side hardness and interlocked, which produces an unusual and shear. attractive mottled figure when sliced or cut on The heartwood of apamate is generally the quarter. rated as durable to very durable with respect to Although its weight is only 85 percent that fungus attack; the darker colored and heavier of English oak, avodire has almost identical

1-23 strength properties except that it is lower in Balsa possesses several characteristics that shock resistance and in shear. The wood works make possible a wide variety of uses. It is the fairly easily with hand and machine tools and lightest and softest of all woods on the market. finishes well in most operations. The lumber selected for use in the United Figured material is usually converted into States when dry weighs on the average of about veneer for use in decorative work and it is 11 pounds per cubic foot and often as little as this kind of material that is chiefly imported 6 pounds. Because of its light weight and ex- into the United States. ceedingly porous composition, balsa is highly efficient in uses where buoyancy, insulation Bagtikan against heat and cold, or absorption of sound and vibration are important considerations. The genus consists of about The wood is readily recognized by its light seven species occurring in . The weight, white to very pale gray color, and its principal species in the United States lumber unique "velvety" feel. trade is bagtikan (P. plicata) of the Philip- The principal uses of balsa are in life-saving pines and . White seraya (P. malagno- equipment, floats, rafts, core stock, insulation, nan) from is also important. In the cushioning, sound modifiers, models, and novel- United States, bagtikan may be encountered ties. Balsa is imported in larger volume than under its usual common name or more fre- most of the foreign woods entering the United quently with the species comprising the light- States. red group of lauans. The heartwood is gray to straw colored or very pale brown and some- Banak times has a pinkish cast. It is not always clearly demarcated from the sapwood. The wood More than 40 species of Virola occur in weighs about 34 pounds per cubic foot at 12 tropical America, but only three species sup- percent moisture content. The texture is similar ply the bulk of the timber known as banak. to that of the light-red group of Philippine These are: V. koschnyi of Central America, lauans. The grain is interlocked and shows a and F. surinamensis and F. sebifera of rather widely spaced stripe pattern on quar- northern South America. tered surfaces. The heartwood is usually pinkish brown or With respect to strength, Philippine - grayish brown in color and is not differentiated tikan exceeds the lauans in all properties. Its from the sapwood. The wood is straight natural durability is very low and it is resist- grained and is of a medium to coarse texture. ant or extremely resistant to preservative The various species are nonresistant to de- treatment. cay and insect attack but can be readily treated with preservatives. Their machining properties The wood works fairly easily with hand and are very good, but fuzzing and grain tearing machine tools and has little blunting effect on are to be expected when zones of tension wood tool cutting edges. are present. The wood finishes readily and is Bagtikan is used for many of the same pur- easily glued. It is rated as a first-class veneer poses as the Philippine lauans, but in the solid species. Its strength properties are similar to form and in thin stock it is best utilized in the yellow-poplar. quartersawn condition to prevent excessive Banak is considered as a general utility wood movement with changes in moisture conditions in both lumber and plywood form. of service. It is perhaps most useful as a veneer for plywood purposes. In Britain it is best known as a decking timber which has been Basra Locus (See Angélique) specially selected for this use in vessels.

Balsa Benge Although benge ( arnoldiana) Balsa ( pyramidale) is widely dis- and ehie (G, ehie) belong to the same botani- tributed throughout tropical America from cal genus, they differ rather markedly with southern Mexico to southern and , respect to their color. The heartwood of benge but Ecuador has been the principal area of is a yellow-brown to medium brown with gray growth since the wood gained commercial im- to almost black striping. Ehie heartwood tends portance. to be a more golden brown and is striped as in 1-24 benge. Ehie appears to be the more attractive Carapa (See Andiroba) of the two species. The technical aspects of these species have Cativo not been investigated, but both are moderately Cativo {Prioria copaifera) is one of the few hard and heavy. Benge is fine textured and in tropical American species that occur in abun- this respect similar to birch; the texture of dance and often in nearly pure stands. Com- ehie is somewhat coarser. Both are straight mercial stands are found in Nicaragua, Costa grained or have slightly interlocked grain. Rica, Panama, and . The sapwood is These woods are as yet little known in the usually thick, and in trees up to 30 inches in United States, but would provide both veneer diameter the heartwood may be only 7 inches and lumber for decorative purposes and furni- in diameter. The sapwood that is utilized com- ture manufacture. mercially may be a very pale pinkish color or may be distinctly reddish. The grain is straight Capirona and the texture of the wood is uniform, com- parable to that of mahogany. Figure on flat- sawn surfaces is rather subdued and results A genus of about five species found through- from the exposure of the narrow bands of out most of Latin America. The species best parenchyma tissue. Odor and taste are not dis- known in the United States and particularly tinctive, and the luster is low. in the archery field is degame {Calycophyllum The wood can be seasoned rapidly and easily candidissimum) y which was imported in the with very little degrade. The dimensional sta- past in some quantities from Cuba. Capirona bility of the wood is very good ; it is practically (C spruceanum) of the Amazon Basin is a equal to that of mahogany. Cativo is classed as much larger tree and occurs in considerably a nondurable wood with respect to decay and greater abundance than degame. insects. Cativo may contain appreciable quan- The heartwood of degame ranges from a light tities of gum, which may interfere with brown to gray, while that of capirona has a finishes. In wood that has been properly sea- distinct yellowish cast. The texture is fine and soned, however, the gum presents no difficulties. uniform. The grain is usually straight or in- The tendency of the wood to bleed resinous frequently shows a shallow interlocking, which material in use and in warping of narrow cut- may produce a narrow and indistinct strip on tings kept this species in disfavor for many quartered faces. The luster is medium and the years. Improved drying and finishing tech- wood is without odor and taste. The wood niques have materially reduced the prominence weighs about 50 pounds per cubic foot. of these inherent characteristics, and the uses Natural durability is low when the wood is for this wood are rapidly increasing. Consider- used under conditions favorable to stain, decay, able quantities are used for interior trim, and and insect attack. resin-stabilized veneer has become an impor- In strength, degame is above the average tant pattern material, particularly in the auto- for woods of similar density. Tests show motive industry. Cativo is widely used for degame superior to persimmon (Diospyros vir- furniture and cabinet parts, lumber core for giniana) in all respects but hardness. Limited plywood, picture frames, for tests on hardness of capirona from gave doors, and bases for piano keyboards. higher values of side hardness than those of Cedro (See Spanish-Cedar) degame or persimmon. Degame is moderately difficult to machine Cedro Macho (See Andiroba) because of its density and hardness, although Cocal (See Sande) it produces no appreciable dulling effect on cut- ting tools. Machined surfaces are very smooth. Courbaril Degame and capirona are little used in the The genus Hymenaea consists of about 30 United States at the present time, but the char- species occurring in the West Indies and from acteristics of the wood should make it particu- southern Mexico, through Central America, larly adaptable for shuttles, picker sticks, and into the Amazon Basin of South America. The other textile industry items in which resilience best known and most important species is H, and strength are required. It should find ap- courbaril, which occurs throughout the range plication for many of the same purposes as of the genus. hard maple and yellow birch. Courbaril sapwood is gray-white and usually

1-25 quite wide. The heartwood is sharply differen- Tests made at the Forest Products Labora- tiated and varies through shades of brown to tory indicate no potential difficulties in the an occasional purplish cast. The texture is me- machining of gola. It also peels and slices very dium. Grain is interlocked, and luster is fairly well. high. The heartwood is without distinctive odor Gola is a very recent newcomer to the timber or taste. The wood weighs about 50 pounds per market and its potential has yet to be developed. cubic foot at 12 percent moisture content. Its workability and relatively light color should The strength properties of courbaril are quite permit utilization in both the solid and veneer high but very similar to those of shagbark form for both utility and decorative purposes. hickory, species of lower specific gravity. In decay resistance, courbaril is rated as very Goncalo Alves durable to durable. Courbaril can be finished smoothly, and it The major and early imports of goncalo alves turns and glues well. It compares favorably {Astronium graveolens & fraxinifolium) have with white oak in steam-bending behavior. been from Brazil. These species range from Courbaril has been little utilized in the United southern Mexico, through Central America into States, but should find application for a the Amazon Basin. number of uses. Its high shock resistance rec- The heartwood ranges from various shades ommends it for certain types of sporting equip- of brown to red with narrow to wide, irregular ment, or as a substitute for ash in handle stock. stripes of dark brown or nearly black. The It promises to be a suitable substitute for sapwood is grayish white and sharply demar- white oak in steam-bent boat parts. It makes cated from the heartwood. The texture is me- an attractive veneer and should also find appli- dium and uniform. Grain is variable from cation in the solid form for furniture. The straight to interlocked and wavy. The wood is thick sapwood would provide a excellent source very heavy and averages about 63 pounds per of blond wood. cubic foot at 12 percent moisture content. It turns readily, finishes very smoothly, and takes a high natural polish. The heartwood is Crabwood (See Andiroba) highly resistant to moisture absorption and the pigmented areas, because of their high density, Cuangare (See Virola) may present some difficulties in gluing. The heartwood is rated as very duralïle with Degame (See Capirona) respect to fungus attack. The high density of the wood is accompanied by equally high strength values, which are Ehie (See Benge) considerably higher in most respects than those of any well known U.S. species. It is not ex- Encino (See Oak) pected, however, that goncalo alves will be im- ported for purposes where strength is an im- portant criterion. Freijo (See Laurel) In the United States the greatest value of goncalo alves is in its use for specialty items Gola such as archery bows, billiard cue butts, brush backs, cutlery handles, and for fine and attrac- Gola {Tetraberlinia tubmaniana) is known tive products of turnery or carving. presently only from . The names "Afri- can pine" and "Liberian pine" have been ap- Greenheart plied to this species, but because it is a hard- wood and not a pine, these names are most Greenheart (Ocotea rodiaei) is essentially a inappropriate and very misleading. Guyana tree although small stands also occur The heartwood is light reddish brown and is in Surinam. The heartwood varies in color from distinct from the lighter colored sapwood, light to dark olive-green or nearly black. The which may be up to 2 inches thick. The wood texture is fine and uniform. is moderately coarse textured. Luster is me- Greenheart is stronger and stiff er than white dium. Grain is interlocked, showing a narrow oak and generally more difficult to work with stripe pattern on quartered surfaces. The wood tools because of its high density. The heart- weighs about 39 pounds per cubic foot at 12 wood is rated as very resistant to decay and percent moisture content. . It also is very resistant to marine

1-26 borers in temperate waters but much less so stances, separate the log into concentric shells. in warm tropical waters. Jarrah is a heavy, hard timber possessing Greenheart is used principally where correspondingly high strength properties. It is strength and resistance to wear are required. resistant to attack by termites and rated as Uses include ship and dock building, lock gates, very durable with respect to fungus attack. The wharves, piers, jetties, engine bearers, - heartwood is rated as extremely resistant to ing, flooring, bridges, and trestles. preservative treatment. Jarrah is fairly hard to work in machines Curjun (See Apitong) and difficult to cut with hand tools. Jarrah is used for decking and underfram- llomba ing of piers, jetties, and bridges, and also for piling and fenders in dock and harbor installa- Ilomba ( angolensis) is a tree of tions. As a flooring timber it has a high resist- the rain forest and ranges from Guinea and ance, but is inclined to splinter under heavy Sierra Leone through west tropical to traffic. and Angola. This species is also re- ferred to in the literature under the synonym- Jelutong ous name Pycnanthus kombo. The wood is a grayish white to pinkish brown Jelutong () is an important and in some trees may be a uniform light species in Malaya where it is best known for its brown. There is generally no distinction be- production rather than its timber. tween heartwood and sapwood. The texture is The wood is white or straw-colored and there moderately coarse and even. Luster is low. is no differentiation between heartwood and Grain is generally straight. The wood weighs sapwood. The texture is moderately fine and about 32 pounds per cubic foot at 12 percent even. The grain is straight, and luster is low. moisture content. This species is generally sim- The wood weighs about 29 pounds per cubic ilar to banak (Virola), but is somewhat coarser foot at 12 percent moisture content. textured. The wood is reported to be very easy to The wood is rated as perishable, but per- season with little tendency to split or warp, meable to preservative treatment. The general but staining may cause trouble. characteristics of ilomba would suggest similar- It is easy to work in all operations, finishes ity to banak in working properties, seasoning, well, and can be glued satisfactorily. finishing, and utilization. The wood is rated as nondurable, but readily This species has been utilized in the United permeable to preservatives. States only in the form of plywood for general Jelutong would make an excellent core stock utility purposes. if it were economically feasible to fill the latex channels which radiate outward in the stem at Ipe (See Lapacho) the branch whorls. Because of its low density and ease of working, it is well suited for sculp- Jacaranda (See , Brazilian) ture and pattern. Jelutong is essentially a "short-cutting" species, because the wood be- Jarrah tween the channels is remarkably free of other defects. rah ( marginata) is native to the coastal belt of southwestern Australia and Kapur one of the principal timbers of the sawmill industry. The genus Dryobalanops comprises some The heartwood is a uniform pinkish to dark nine species distributed over parts of Malaya, red, often a rich, dark red mahogany hue, turn- Sumatra, and Borneo, including North Borneo ing to a deep brownish red with age and ex- and . For the export trade, however, posure to light. The sapwood is pale in color the species are combined under the name kapur. and usually very narrow in old trees. The tex- The heartwood is light reddish brown, ture is even and moderately coarse. The grain, clearly demarcated from the pale colored sap- though usually straight, is frequently inter- wood. The wood is fairly coarse textured but locked or wavy. The wood weighs about 44 uniform. In general appearance the wood re- pounds per cubic foot at 12 percent moisture sembles that of apitong and keruing, but on content. The common defects of jarrah include the whole it is straighter grained and not quite gum veins or pockets which, in extreme in- so coarse in texture. The Malayan timber aver-

1-27 ages about 48 pounds per cubic foot at 12 per- found in the coastal belt of the so-called closed cent moisture content. or . The closely allied species, Strength property values available for D. anthothecŒy has a more restricted range and is lanceolata show it to be on a par with apitong found farther inland in regions of lower rain- or keruing of similar specific gravity. fall but well within the area now being worked The heartwood is rated as very durable and for the export trade. extremely resistant to preservative treatment. The heartwood varies from a pale pink to a The wood works with moderate ease in most dark reddish brown. The grain is interlocked, hand and machine operations. A good surface and the texture is equal to that of mahogany is obtainable from the various machining oper- (), The wood is very well known in ations, but there is a tendency toward "raised the United States and large quantities are im- grain" if dull cutters are used. It takes nails ported annually. The wood is easy to season, and screws satisfactorily. machines and finishes well. In decay resist- The wood provides good and very durable con- ance, it is generally rated below American ma- struction timbers and is suitable for all the hogany. purposes for which apitong and keruing are Principal uses include furniture, interior fin- used in the United States. ish, boat construction, and veneer.

Karri Kokrodua

Karri {Eucalyptus diversicolor) is a very Kokrodua () is the verna- large tree limited to Western Australia, oc- cular name used in . It is also known as curring in the southwestern portion of the afrormosia, its former generic name. state. This large West African tree shows promise Karri resembles jarrah (E. marginata) in of becoming a substitute for teak ( structure and general appearance. It is usually grandis). The heartwood is fine textured, with paler in color, and, on the average, slightly straight to interlocked grain. The wood is heavier (57 lb. per cu. ft. at 12 pet. m.c). brownish yellow with darker streaks, moder- The heartwood is rated as moderately dur- ately hard and heavy, weighing about 44 able and extremely resistant to preservative pounds per cubic foot at 15 percent moisture treatment. content. The wood strongly resembles teak in Karri is a heavy hardwood possessing me- appearance but lacks the oily nature of teak chanical properties of a correspondingly high and is finer textured. order. The wood seasons readily with little degrade The wood is fairly hard to work in machines and has good dimensional stability. It is some- and difficult to cut with hand tools. It is gen- what heavier than teak and stronger. The erally more resistant to cutting than jarrah heartwood appears to be highly resistant to and has slightly more dulling effect on tool decay and should prove extremely durable un- edges. der adverse conditions. The wood can undoubt- It is inferior to jarrah for underground use edly be used for the same purposes as teak, and waterworks, but where flexural strength such as boat construction, interior trim, and is required, such as in bridges, floors, rafters, decorative veneer. and beams, it is an excellent timber. Karri is popular in the heavy construction field because of its strength and availability in large sizes Korina (See Limba) and long lengths that are free of defects. Krabak (See Mersawa) Keruing (See Apitong) Lapacho Khaya The lapacho group or series of the genus The bulk of the khaya or "African Mahog- Tabebuia consists of about 20 species of trees any" 2 shipped from west central Africa is and occurs in practically every Latin Ameri- Khaya ivorensis, which is the most widely dis- can country except Chile. Another commonly tributed and most plentiful species of the genus used name is ipe. The sapwood is relatively thick, yellowish ' Forest Service nomenclature restricts the name mahogany to the species belonging to the botanical gray or gray brown and sharply differentiated genus Swietenia, from the heartwood, which is a light to dark

1-28 olive brown. The texture is fine. Grain is closely any'" specify that mayapis be excluded from and narrowly interlocked. Luster is medium. their shipments. The wood is very heavy and averages about 64 "Philippine " as a whole have a pounds per cubic foot at 12 percent moisture coarser texture than mahogany or the "African content. Thoroughly air-dried specimens of mahoganies" and do not have the dark colored heartwood generally sink in water. deposits in the pores. Forest Products Labora- Lapacho is moderately difficult to machine tory studies showed that the average decay re- because of its high density and hardness. sistance was greater for mahogany than for Glassy smooth surfaces can be readily pro- either the "African mahoganies" or the duced. "Philippine mahoganies." The resistance of Being a very heavy wood, lapacho is also "African mahogany" was of the moderate type very strong in all properties and in the air-dry and seemed no greater than that of some of the condition is comparable to greenheart. "Philippine mahoganies." Among the Philip- Lapacho is highly resistant to decay and pine species, the woods classified as "dark red insects, including both subterranean and dry- Philippine mahogany" usually were more resis- wood termites. It is, however, susceptible to tant than the woods belonging to the light red marine borer attack. The heartwood is imper- group. meable, but the sapwood can be readily treated In machining trials made at the Laboratory, with preservatives. the Philippine species appeared to be about Lapacho is used almost exclusively for heavy equal with the better of the hardwoods found duty and durable construction. Because of its in the United States. Tanguile was consistently hardness (two to three times that of oak or better than average in all or most of the tests. apitong) and very good dimensional stability, Mayapis, almon, and white lauan were con- it would be particularly well suited for heavy sistently below average in all or most of the duty flooring in trucks and box cars. trials. Red lauan and bagtikan were inter- mediate. All of the species showed interlocked Lauans grain. The term "lauan" or "Philippine ma- The shrinkage and swelling characteristics hogany" is applied commercially to Philip- of the Philippine species are comparable to pine woods belonging to three genera—, those found in the oaks and maples of the Parashorea, and Pentacme, These woods are United States. usually grouped by the United States trade Principal uses include interior trim, panel- into "dark red Philippine mahogany" and ing, flush doors, plywood, cabinets, furniture, "light red Philippine mahogany." The species siding, and boat construction. The use of the found in these two groups and their heart- woods of the dark red group for boatbuilding wood color are: in the United States exceeds in quantity that of any foreign wood. Dark red Philippine mahogany" Red lauan, Shorea Dark reddish-brown to brick red Laurel negrosensis Tanguile, Shorea Red to reddish-brown polysperma The genus Cordia contains numerous spe- Tianong, Shorea Light red to light reddish-brown cies, but only a relatively small number are agsaboensis trees of commercial size. The three most im- "Light red Philippine mahogany" portant species are Cordia alliodora (laurel) with the most extensive range from the West Almon, Light red to pinkish Bagtikan, Parashorea Grayish-brown Indies and Mexico southward to northern Bo- plicata livia and eastern Peru; C. goeldiana (freijo) Mayapis, Shorea Light red to reddish-brown squamata of the Amazon Basin; and C. trichotoma (pete- White lauan, Grayish to very light red rebi) of southeastern Brazil, northern Argen- Pentacme contorta tina, and adjacent Paraguay. The species within each group are shipped The heartwood is light to medium brown, interchangeably when purchased in the form plain or frequently with a pigment figure out- of lumber. Mayapis of the light red group is lining the growth ring pattern. Sapwood is quite variable with respect to color and fre- generally distinct and of a yellowish or very quently shows exudations of resin. For this light brown color. Grain is generally straight reason, some purchasers of "Philippine mahog- or shallowly interlocked. Texture is medium

1-29 and uniform. The wood is variable in weight, also used for such articles as , pulley but in the same density range as mahogany sheaves, caster wheels, stencil and block, and cedro. various turned articles, and brush backs. The wood and machines easily with Vera or verawood (Bulnesia arbórea) of good to excellent results in all operations. It Colombia and Venezuela is sometimes sub- is reported to glue readily and holds its place stituted for ; however, vera is not well when manufactured. suitable for underwater bearings. The Cordia woods are rated as moderately durable to durable when used in contact with Limba the ground, and are rated slightly above mahogany with respect to resistance against Abundant supplies of limba {Terminalia drywood termites. The darker colored wood is superba) occur in west central Africa and the reputed to be more durable with respect to Congo region. decay and have better resistance than The wood varies in color from a gray-white the lighter colored material. to creamy brown and may contain dark The strength properties of these Cordias streaks, which are valued for special purposes. are generally on a par with those of mahogany The light colored wood is considered an im- and cedro. portant asset for the manufacture of blond Because of their ease of working, good dura- furniture. The wood is generally straight bility, low shrinkage, and attractiveness, the grained and of uniform but coarse texture. woods are used extensively within their areas The wood is easy to season and the shrink- of growth for furniture, cabinetwork, general age is reported to be rather small. Limba is not construction, boat construction and many resistant to decay, insects, or termites. It is other uses. The characteristics of the wood easy to work with all types of tools and is should qualify it for use in the United States veneered without difficulty. for many of the same purposes as mahogany Principal uses include interior trim, panel- and cedro. ing, and furniture. Selected limba plywood is sold in the United States under the copy- Lignum Vitae righted name, "korina."

Lignum vitae (Guaiacum offmcde) native Lupuna to the West Indies, northern Venezuela, north- ern Colombia, and Panama, was for a great Lupuna (Ceiba samavmia) is a very large many years the only species used on a large tree found in the Amazon Basin. In the Peru- scale. With the near exhaustion of commercial- vian-Amazon region it is known as lupuna. In its Brazilian range it is known as samauma. size timbers of G. officinale the principal spe- The wood is white or grayish to very pale red- cies of commerce is now G. sanctum. The dish, very soft and light, weighing about 25 latter species occupies the same range as G. pounds per cubic foot air dry. The wood is officinale, but is more extensive and includes the coarse textured and has a dull luster. It is Pacific side of Central America as well as nondurable with respect to decay and insect southern Mexico and southern Florida. attack. Some of the veneer used for plywood Lignum vitae is one of the heaviest and cores has been known to give off highly ob- hardest woods on the market. The wood is jectionable odor when subjected to high hum- characterized by its unique green color and idity. oily or waxy feel. The wood has a fine, uni- The wood is available in large sizes, and its form texture and closely interlocked grain. low density combined with a rather high de- Its resin content may constitute up to about gree of dimensional stability make it ideally one-fourth of the air-dry weight of the heart- suited for pattern and core stock. wood. The mechanical properties have not been Lignum vitae wood is used chiefly for bear- investigated. ing or bushing blocks for the lining of stern tubes of steamship propeller shafts. The great Mahogany strength and tenacity of lignum vitae, com- Mahogany () ranges bined with the self-lubricating properties that from southern Mexico through Central are due to the high resin content, make it America into South America as far south as especially adaptable for underwater use. It is Bolivia. Mexico, Belize, and Nicaragua furnish

1-30 about 70 percent of the mahogany imported weight utility hardwood and comprises those into the United States. species yielding a red or reddish but not a The heartwood varies from a pale to a dark dark red timber. The actual color of the heart- reddish brown. The grain is generally straighter wood varies from pale pink to light reddish than that of "African mahogany;" however, brown. The weight of the wood may vary over a wide variety of grain patterns are obtained a rather wide range from 25 to 44 pounds per from this species. cubic foot in the seasoned condition. Among the properties that mahogany pos- Dark red meranti is darker in color than sesses to a high degree are dimensional sta- ordinary red meranti and appreciably heavier, bility, fine finishing qualities, and ease of work- weighing on the average about 43 pounds per ing with tools. The wood is without odor or cubic foot seasoned. This color variation is the taste. It weighs about 32 pounds per cubic product of a more limited number of species foot at 12 percent moisture content. and consequently tends to be more uniform in The principal uses for mahogany are furni- character than light red meranti. Because of ture, models and patterns, boat construction, the number of species contributing to the radio and television cabinets, caskets, interior production of meranti, appreciable variation trim, paneling, precision instruments, and may be encountered with respect to mechani- many other uses where an attractive and di- cal and physical properties, durability, and mensionally stable wood is required. working characteristics. The wood is used in both plywood and solid Mahogany, African (See Khaya) form for much the same purposes as the Philip- pine lauans. Mahogany, Philippine (See Lauans) Mersawa Mayapis (See Lauans) Mersawa is one of the Anisoptera, a genus Mayflower (See Apamate) of about 15 species distributed from the Philip- pine Islands and to East Pakistan. Meranti Names applied to the timber vary with the source and three names are generally encount- The trade name meranti covers a number ered in the lumber trade: krabak (Thailand), of closely related species of Shorea from mersawa (Malaysia), and palosapis (Philip- which light or only moderately heavy timber pines). is produced. This timber is imported from The Anisoptera species produce wood of Malaysia and Indonesia. On the Malay Pen- light color and moderately coarse texture. The insula this timber is commonly classified for heartwood when freshly sawn is pale yellow export either as light red or dark red meranti. or yellowish brown and darkens on exposure. Each of these color varieties is the product of Some timber may show a pinkish cast or pink several species of Shorea. Meranti exported streaks, but these eventually disappear on ex- from Sarawak and various parts of Indonesia posure. The wood weighs about 39 pounds per is generally similar to the Malayan timber. cubic foot in the seasoned condition at 12 per- Meranti corresponds roughly to seraya from cent moisture content and about 59 pounds North Borneo and lauan from the , when green. which are names used for the lighter types of The sapwood is susceptible to attack by Shorea and allied genera. powderpost beetles and the heartwood is not Meranti shows considerable variation in resistant to termites. With respect to fungus color, weight, texture, and related properties, resistance, the heartwood is rated as moder- according to the species. The grain tends to ately resistant and should not be used under be slightly interlocked so that quartered stock conditions favoring decay. The heartwood does shows a broad stripe figure. The texture is not absorb preservative solutions readily. moderately coarse but even. Resin ducts with The wood machines readily, but because of or without white contents occur in long tan- the presence of silica, the dulling effect on gential lines on the end surfaces of the wood, the cutting edges of ordinary tools is severe but the wood is not resinous like some of the and is very troublesome with saws. keruing species. Wood from near the center of It appears probable that the major volume the log is apt to be weak and brittle. of these timbers will be used in the form of Light red meranti is classed as a light- plywood, because conversion in this form pre-

1-31 sents considerably less difficulty than lumber The wood of the various species is in most production. cases heavier than the species of the United States. Nogal, Tropical Walnut Strength data are available for only four species and the values obtained fall between Nogal or tropical walnut includes two spe- those of white oak and the southern live oak cies, Juglans neotropica of the eastern slope or are equal to those of the latter. The average of the Andes and /. olanchana of northern specific gravity for these species is 0.72 based Central America. There is widespread interest on volume when green and weight ovendry, in walnut from sources where lumber costs are with an observed maximum average for one decidedly lower than in the United States, species from Guatemala of 0.86. but unfortunately little technical information Utilization of the tropical oaks is very is available regarding these species. limited at present due to difficulties encount- The wood of the tropical species is generally ered in the drying of the wood. The major darker than that of typical American black volume is used in the form of charcoal. walnut, and the texture (pore size) is some- what coarser. From the limited number of Obeche specimens available for examination, nogal also appears to be somewhat lighter in weight Obeche () trees of than U.S. black walnut. Logs frequently show west central Africa reach heights of 150 feet streaks of lighter color in the heartwood and or more and diameters of up to 5 feet. The this characteristic has caused some concern trunk is usually free of branches for consider- about the potential utility of the tropical wood. able heights so that clear lumber of considera- Other features that are mentioned whenever ble size is obtainable. tropical walnut is under discussion are the The wood is creamy white to pale yellow extreme slowness with which the wood dries with little or no difference between the sap- and the dull yellowish-green coloring of the wood and heartwood. It is fairly soft, of uni- inner portion of some boards that occurs dur- form texture, and the grain is straight or more ing drying. It has been stated that lumber to often interlocked. The wood weighs about 24 %-inch thickness can be dried at the same rate pounds per cubic foot in the air-dry condition. as American black walnut, but thicker stock The wood seasons readily with little degrade. takes an appreciably longer period of time, and It is not resistant to decay, and the sapwood in the thicker stock the wood is prone to blue stains readily unless appropriate precau- collapse and honeycomb. tions are taken after the trees are felled as Tropical walnut peels and slices readily, but well as after they have been converted into the veneer is said to dry more slowly than lumber. American black walnut. Tension wood and The wood is easy to work and machine, ve- compression failures have been observed in a neers and glues well, and takes nails and number of specimens, and these invariably screws without splitting. came from the central core of the tree. The characteristics of this species make it It appears that these species require rather especially suitable for veneer and core stock. intensive study, particularly with respect to This species is also called samba and wawa. seasoning and machining, in order to ascertain their true potential. Okoume

Oak The natural distribution of okoume (Au- coumea klaineana) is rather restricted and The oaks (Quercus spp.) are abundantly is found only in west central Africa and represented in Mexico and Central America Guinea. This species has been popular in with about 150 species, which are nearly European markets for many years, but its equally divided between red and white oak extensive use in the United States is rather groups. Mexico is represented with over 100 recent. When first introduced in volume in the species and Guatemala with about 25; the plywood and door fields, its acceptance was numbers diminish southward to Colombia, phenomenal because it provided attractive ap- which has two species. The usual Spanish pearance at moderate cost. The wood has a name applied is encino or roble and no dis- salmon-pink color with a uniform texture and tinction is made in the use of these names. high luster. The texture is slightly coarser than

1-32 that of birch. Okoume offers unusual flexibility Pau Marfîm in both working and finishing because the color, which is of medium intensity, permits toning to The growing range of Pau marfim (Bal- either lighter or darker shades. fourodendron riedelianum) is rather limited, In this country it is used for decorative extending from the State of Sao Paulo, Brazil, plywood paneling, general utility plywood, and into Paraguay and the provinces of Corrientes for doors. Its use as solid lumber has been and Missiones of northern . In hampered because special saws and planer Brazil it is generally known as pau marfim knives are required to effectively machine this and in Argentina and Paraguay as guatambu. species because of the silica content of the In color and general appearance the wood wood. is very similar to birch or hard maple sap- wood. Although growth rings are present, they Palosapis (See Mersawa) do not show as distinctly as in birch and maple. The wood is straight grained, easy to "Parana Pine" work and finish but is not considered to be resistant to decay. There is no apparent dif- The wood that is commonly called "Parana ference in color between heartwood and sap- pine" ( angustifolia) is not a true wood. pine. It is a softwood that comes from south- The average specific gravity of pau marfim eastern Brazil and adjacent areas of Paraguay is about 0.63 based on the volume when green and Argentina. and weight when ovendry. On the basis of "Parana pine" has many desirable char- its specific gravity, its strength values would acteristics. It is available in large sizes of be above those of hard maple which has an clear boards with uniform texture. The small average specific gravity of 0.56. pinhead knots (leaf traces) that appear on In the areas of growth it is used for much flat-sawn surfaces and the light brown or red- the same purposes as our native hard maple dish-brown heartwood, which is frequently and birch. Pau marfim was introduced to the streaked with red, provide desirable figured U.S. market in the late 1960's and has been effects for matching in paneling and interior very well received and is especially esteemed finishes. The growth rings are fairly distinct for turned items. and more nearly like those of white pine (Pinus strobus) rather than those of the yel- Peroba de Campos low pines. The wood has relatively straight grain, takes paint well, glues easily, and is Peroba de campos (Paratecoma peroba) oc- free from resin ducts, pitch pockets, and curs in the coastal forests of eastern Brazil streaks. ranging from Bahia to Rio de Janeiro. It is The strength values of this species compare the only species in the genus. favorably with those softwood species of simi- The heartwood is variable in color, but gen- lar density found in the United States and, erally is in shades of brown with tendencies in some cases, approach the strength values toward casts of olive and reddish color. The of species with greater specific gravity. It is sapwood is a yellowish gray, clearly defined especially good in shearing strength, hardness, from the heartwood. The texture is relatively and -holding ability, but notably deficient fine and approximates that of birch. The wood in strength in compression across the grain. averages about 47 pounds per cubic foot at Some tendency towards splitting of kiln- 12 percent moisture content. dried "Parana pine" and warping of seasoned The wood machines easily, but when smooth and ripped lumber is caused by the presence surfaces are required particular care must be of compression wood, an abnormal type of wood structure with intrinsically large shrink- taken in planing to prevent excessive grain age along the grain. Boards containing com- tearing of quartered surfaces because of the pression wood should be excluded from exact- presence of interlocked or irregular grain. ing uses. The principal uses of "Parana pine" There is some evidence that the fine dust include framing lumber, interior trim, sash arising from machining operations may pro- and door stock, furniture, case goods, and duce allergic responses in certain individuals. veneer. Peroba de campos is heavier than teak or This species is known in Brazil as pinheiro white oak and is proportionately stronger than do Parana or pinho do Parana. either of these species.

1-33 The heartwood is rated as very durable The strength properties of ocote pine are with respect to fungus attack and is rated as comparable in most respects with those of resistant to preservative treatment. longleaf pine (P. palustris). In Brazil, the wood is used in the manu- Decay resistance studies show ocote pine facture of fine furniture, flooring, and decora- heartwood to be very durable with respect to tive paneling. The principal use in the United attack by a white-rot fungus and moderately Sates is in shipbuilding, where it serves as durable with respect to brown rot. an alternate for white oak for all purposes Ocote pine is comparable to the southern except bent members. The wood is classified pines in workability and machining character- as a poor "bender." istics. Ocote pine is a general construction timber and is suited for the same uses as the southern Peterebi (See Laurel) pines.

Pine, Caribbean Primavera

Caribbean pine (Pintes caribaea) occurs The natural distribution of primavera (Cy- along the Caribbean side of Central America bistax donnell-smithii) is restricted to south- from Belize to northeastern Nicaragua. It is western Mexico, the Pacific coast of Guatemala also native to the Bahamas and Cuba. It is and El Salvador, and north central Honduras. primarily a tree of the lower elevations. Primavera is regarded as one oT the pri- The heartwood is a golden brown to red ;mary light-colored woods, but its use was brown and distinct from the sapwood which limited because of its rather restricted range is 1 to 2 inches in thickness and a light yel- and the relative scarcity of wild trees within low. The wood has a strong resinous odor and its natural growing area. a greasy feel. The wood averages about 51 now coming into production pounds per cubic foot at 12 percent moisture have increased the availability of this species content. and provided a more constant source of supply. The lumber can be kiln dried satisfactorily The quality of the plantation-grown wood is using the same schedule as that for ocote pine. equal in all respects to that obtained from Caribbean pine is easy to work in all machin- wild trees. ing operations but the high resin content The heartwood is whitish to straw-yellow may necessitate occasional stoppages to per- and in some logs may be tinted with pale mit removal of accumulated resin from the brown or pinkish streaks. The wood has a equipment. very high luster. Caribbean pine is an appreciably heavier Primavera produces a wide variety of figure wood than slash pine (P. elliottii), but the patterns. mechanical properties of these two species are The shrinkage properties are very good, and rather similar. the wood shows a high degree of dimensional Caribbean pine is used for the same pur- stability. Although the wood has considerable poses as the southern pines of the United grain variation, it machines remarkably well. States. With respect to decay resistance it is rated as durable to very durable. Pine, Ocote The dimensional stability, ease of working, and pleasing appearance recommend primavera Ocote pine (Pinus oocarpa) is a species of for solid furniture, paneling, interior trim, and the higher elevations and occurs from north- special exterior uses. western Mexico southward through Guatemala into Nicaragua. The largest and most exten- Ramin sive stands occur in northern Nicaragua and Honduras. Ramin { bancanus) is one of the The sapwood is a pale yellowish brown and very few moderately heavy woods that are generally up to 3 inches in thickness. The classified as a ''blond" wood. This species is heartwood is a light reddish brown. Grain is native to southeast Asia from the Malay Penin- straight. Luster is medium. The wood has a sula to Sumatra and Borneo. resinous odor, and weighs about 41 pounds The wood is a uniform pale straw or yel- per cubic foot at 12 percent moisture content. lowish to whitish in color. The grain is straight 1-34 or shallowly interlocked. The texture is moder- backs, billiard cue butts, and fancy articles of ately fine, similar to that of mahogany (Swie- turnery. tenia)y and even. The wood is without figure or luster. Ramin is moderately hard and heavy, Rosewood, Indian weighing about 42 pounds per cubic foot in the air-dry condition. The wood is easy to work, Indian rosewood (Dalbergia latifoUa) is na- finishes well, and glues satisfactorily. tive to most provinces of India except in the With respect to natural durability ramin is northwest. rated as perishable, but it is permeable with The heartwood is a dark purplish brown regard to preservative treatment. with denser blackish streaks terminating the Ramin has been used in the United States growth zones and giving rise to an attractive in the form of plywood for doors and in the figure on flat-sawn surfaces. The average solid form for interior trim. weight is about 53 pounds per cubic foot at 12 percent moisture content. The texture is uniform and moderately coarse. The wood of Red lauan (See Lauans) this species is quite similar in appearance to that of the Brazilian and Honduras rosewood. Roble (See Oak) The timber is said to kiln dry well, but rather slowly, and the color is said to improve during drying. Rosewood, Brazilian Indian rosewood is a heavy timber with high strength properties and is particularly hard Brazilian rosewood or Jacaranda (Dalbergia for its weight after being thoroughly sea- nigra) occurs in the eastern forests of the State of Bahia to Rio de Janeiro. Having been soned. The wood is moderately hard to work with exploited for a long period of time it is, at handtools and offers a fair resistance in ma- present, nowhere abundant. chine operations. Lumber containing calcare- The wood of commerce is very variable with ous deposits tends to blunt tools rapidly. The respect to color, ranging through shades of wood turns well and has high -holding brown, red, and violet and is irregularly and properties. Filling of the pores is desirable if conspicuously streaked with black. Many kinds a very smooth surface is required for certain are distinguished locally on the basis of pre- purposes. vailing color. The texture is coarse, and the Indian rosewood is essentially a decorative grain is generally straight. Heartwood has an wood for high-class furniture and cabinet- oily or waxy appearance and feel. The odor is work. In the United States it is used primarily fragrant and distinctive. The wood is hard in the form of veneer. and heavy; thoroughly air-dried wood is just barely floatable in water. The strength properties have not been de- Samauma (See Lupuna) termined, but for the purposes for which Brazil- ian rosewood is utilized they are more than Samba (See Obeche) adequate. In hardness, for example, it exceeds by far any of the native hardwood species Sande used in the furniture and veneer field. The wood machines and veneers well. It can Practically all of the exportation of sande be glued satisfactorily, providing the neces- (Brosimiim spp.-utile group) is from Pacific sary precautions are taken to ensure good glue Ecuador and Colombia. It is also known as bonds as with other woods in this density cocal. class. The sapwood and heartwood show no dis- Brazilian rosewood has an excellent reputa- tinction, being a uniform yellowish white to tion for durability with respect to fungus and yellowish brown or light brown. The pores insect attack, including termites, although are moderately coarse and evenly distributed. the wood is not used for purposes where these The grain is straight to widely and shallowly would present a problem. interlocked. In many respects, sande has much Brazilian rosewood is used primarily in the the same appearance as white ser ay a (Par- form of veneer for decorative plywood. Limited ashorea malaanonan) from Sabah. The wood quantities are used in the solid form for spe- averages about 33 pounds per cubic foot at 12 cialty items such as cutlery handles, brush percent moisture content.

1-35 The wood is nondurable with respect to The heartwood ranges in color from that of stain, decay, and insect attack and care must mahogany to a dark reddish or purplish be exercised to prevent degrade from these brown. The lighter colored and distinct sap- agents. wood may be up to 4 inches thick. Texture is Strength data for sande are too limited to finer than that of mahogany. Grain is inter- permit comparison with woods of similar den- locked and produces a narrow and uniform sity such as banak, although it is suspected stripe pattern on quartered surfaces. The wood that they would be rather similar. averages about 39 pounds per cubic foot at Normal wood of sande machines easily, takes 12 percent moisture content. stains, and finishes readily, and presents no has the same average density as gluing problems. Sande should find utilization white oak, and its mechanical properties are for many of the same purposes as banak, and in general higher than those of white oak. with the current demand for molding species, The wood works fairly easily with machine it should assist in relieving the ever-increas- tools, although interlocked grain offers diffi- ing wood demand of this industry. culties in planing and molding. Sapele finishes and glues well. Santa Maria The heartwood is rated as moderately dur- able and as resistant to preservative treatment. Santa Maria (Calophyllum hrasiliense) Sapele is used extensively, primarily in the ranges from the West Indies to southern Mex- form of veneer for decorative plywood. ico and southward through Central America into northern South America. Spanish-Cedar The heartwood is pinkish to brick red or rich reddish brown and marked by a fine and Spanish-cedar or cedro ( spp.) com- slightly darker striping on flat-sawn surfaces. prises a group of about seven species that are The sapwood is lighter in color and generally widely distributed in tropical America from distinct from the heartwood. Texture is med- southern Mexico to northern Argentina. The ium and fairly uniform. Luster is medium. wood is more or less distinctly ring porous, The heartwood is rather similar in appearance and the heartwood varies from light reddish to the red lauan of the Philippines. The wood brown to dark reddish brown. The heartwood averages about 38 pounds per cubic foot at 12 is characterized by its distinctive cedarlike percent moisture content. odor. The wood is moderately easy to work and The wood seasons readily. It is not high in good surfaces can be obtained when attention strength but is roughly rated to be similar to is paid to machining operations. Central American mahogany in most prop- Santa Maria is in the density class of hard erties except in hardness and compression per- maple and its strength properties are gen- pendicular to the grain where mahogany is erally ^imilar, with the exception of hardness, definitely superior. It is considered decay re- in which property hard maple is superior to sistant and works and glues well. Santa Maria. Spanish-cedar is used locally for all purposes The heartwood is generally rated as mod- where an easily worked, light but strong, erately durable to very durable in contact with straight grained, and durable wood is required. the ground, but apparently has little resis- Spanish-cedar and mahogany are the classic tance against termites and marine borers. timbers of Latin America. The inherent natural durability, color, and figure on the quarter suggest utilization as Tangare (See Andiroba) face veneer for plywood in boat construction. It also offers possibilities for use in flooring, Tanguile (See Lauans) furniture, cabinetwork, millwork, and decora- tive plywood. Teak Teak (Tectona grandis) occurs in commer- Sapele cial quantities in India, Burma, Thailand, Laos, Cambodia, North and South Vietnam, and Sapele ( cylindHcum) is a the East Indies. Numerous plantations have large African rain forest tree ranging from been developed within its natural range and Sierra Leone to Angola and eastward through tropical areas of Latin America and Africa, the Congo to Uganda. and many of these are now producing timber. 1-36 The heartwood varies from a yellow-brown to maple. The wood is rated very low with a rich brown. It has a coarse texture, is usually respect to natural durability; hence it is best straight grained, and has a distinctly oily feel. suited for use under interior conditions. The heartwood has excellent dimensional Currently the wood is being used for panel- stability and possesses a very high degree of ing, interior trim, and core stock. natural durability. The mechanical properties have not been in- Although not generally used in the United vestigated. States where strength is of prime importance, the values for teak are generally on a par with Walnut, European those of our native oaks. Teak generally works with moderate ease Although generally referred to as European with hand and machine tools. Because of the walnut or by its country of origin, walnut presence of silica, its dulling effect on tools is () is a native of western and sometimes considerable. Finishing and gluing central Asia, extending to China and northern are satisfactory although pretreatment may be India. Trees are grown in commercial quanti- necessary to ensure good bonding of finishes ties mainly in Turkey, Italy, France, and Yugo- and glues. slavia. Intrinsically, teak is one of the most valuable Walnut is variable in color, with a grayish- of all woods, but its use is limited by scarcity brown background, marked with irregular dark- and high cost. Teak is unique in that it does colored streaks. The figure, which is due to not cause rust or corrosion when in contact the infiltration of coloring matter, is some- with metal; hence, it is extremely useful in times accentuated by the naturally wavy grain. the shipbuilding industry. It is currently used The highly figured veneers used in cabinet- in the construction of expensive boats, furni- making and decorative paneling are obtained ture, flooring, decorative objects, and veneer for from the stumps, burls, and crotches of a rel- decorative plywood. atively small percentage of the trees. The wood weighs about 40 pounds per cubic foot in the Tianong (See Lauans) air-dry condition. The product of any one locality may vary Verawood (See Lignum Vitae) considerably in color, figure, and texture, but the selected export timber generally shows Virola certain typical characteristics. French walnut is Virola is the common name being currently typically paler and grayer than English walnut, applied to the wood of two or more species of while the Italian wood is characterized by its Dialyanthera originating in the Pacific forests elaborate figure and dark, streaky coloration. of Colombia and Ecuador. The local name for Because of the ease of machining, finishing, and this wood is cuangare, and would be preferred gluing, walnut is used extensively in veneer for common usage because the common name form as well as in the solid form for furni- "virola" is frequently confused with the ture, paneling, and decorative objects. It and botanical genus Virola, American black walnut are the classic woods The wood is a pale pinkish brown with a for rifle stocks. high luster. There is no sharp demarcation between heartwood and sapwood. The wood Walnut, tropical (See Nogal) is generally straight grained, easy to work, holds nails well, and finishes smoothly. The Wawa (See Obeche) texture is quite similar to that of okoume. Virola is a relatively low-density wood. On White lauan (See Lauans) the dry-weight basis, it is equal to that of alder, White seraya (See Bagtikan) aspen, and basswood. Shrinkage properties of virola are about the same as those of sugar Yang (See Apitong)

1-37 BIBLIOGRAPHY Bellosillo, S. B., and Miciano, R. J. 1959. Progress report on the survey of mechanical properties of Philippine woods. The Lum- berman. Philippines. British Forest Products Research Laboratory 1956. A handbook of hardwoods. H. M. Stationery Office, 269 pp. London. 1960. The strength properties of timber. Forest Prod. Res. Bull. 50. H. M. Stationery Office, 34 pp. London. Brown, H. P., Panshin, A. J., and Forsaith, C. C. 1949. Textbook of wood technology. Vol. L Struc- ture, identification, defects, and uses of the commercial woods of the United States. 652 pp. New York. Kukachka, B. F. 1970. Properties of imported tropical woods. USDA Forest Serv. Res. Pap. FPL 125. Forest Prod. Lab., Madison, Wis. Markwardt, L. J. 1930. Comparative strength properties of woods grown in the United States. U.S. Dep. Agr. Tech. Bull. 158, 39 pp. Record, S. J., and Hess, R. W. 1949. Timbers of the new world. Yale Univ. Press, 640 pp. Wangaard, F. F. 1950. Mechanical properties of wood. 377 pp. New York.

1-38 FS-352

Chapter 2

STRUCTURE OF WOOD

Page Bark, Wood, and Pith 2-3 Growth Rings 2-3 Early wood and Late wood 2-4 Sap wood and Heartwood 2-4 Wood Cells 2-4 Chemical Composition of Wood 2-5 Identification 2-6 Bibliography 2-6

2-1 STRUCTURE OF WOOD

The fibrous nature of wood strongly inñu- fibrous cells and their arrangement aiïects such ences how it is used. Specifically, wood is com- properties as strength and shrinkage, as well posed mostly of hollow, elongate, - as grain pattern of the wood. shaped cells that are arranged parallel to each other along the trunk of a tree. When lumber is A brief description of some elements of an- cut from the tree, the characteristics of these atomical structure are given in this chapter.

M 886P0 V

M eeezo Figure 2-1. Cross section of a white oal< tree trunk: A, Cambium layer (microscopic) is inside inner bark and forms wood and bark cells. B, Inner bark is moist, soft, and contains living tissue. Carries prepared food from leaves to all grow- ing parts of tree. C, Outer bark containing corky layers ¡s composed of dry dead tissue. Gives general protection against external injuries. Inner and outer bark are separated by a bark cambium. D, Sapwood, which contains both living and dead tissues, is the light-colored wood beneath the bark. Carries sap from to leaves. E, Heartwood (inactive) is formed by a gradual change in the sapwood. F, Pith is the soft tissue about which the first wood growth fakes place in the newly formed twigs. G, Wood rays connect »he various layers from prth to bark for storage and transfer of food.

2-2 BARK, WOOD, AND PITH formed early and that formed late in a growing season to produce well-marked annual growth A cross section of a tree (fig. 2-1) shows rings. The age of a tree at the stump or the the following well-defined features in succes- age at any cross section of the trunk may be sion from the outside to the center: (1) Bark, determined by counting these rings (fig. 2-2). which may be divided into the outer, corky, dead If the growth of trees in diameter is interrupted part that varies greatly in thickness with dif- by drought or defoliation by insects, more ferent species and with age of trees, and the than one ring may be formed in the same sea- thin, inner living part; (2) wood, which in son. In such an event, the inner rings us- merchantable trees of most species is clearly ually do not have sharply defined boundaries differentiated into sapwood and heartwood ; and and are termed false rings. Trees that have (3) the pith, indicated by a small central core, only very small crowns or that have accident- often darker in color, which represents primary ally lost most of their foliage may form only growth formed when woody stems or branches an incomplete growth layer, sometimes called elongate. a discontinuous ring, until the crown is re- Most branches originate at the pith, and stored. their bases are intergrown with the wood of the trunk as long as they are alive. These living branch bases constitute intergrown knots. After the branches die, their bases con- tinue to be surrounded by the wood of the growing trunk. Such enclosed portions of dead branches constitute the loose or encased knots. After the dead branches drop off, the dead stubs become overgrown and, subsequently, clear wood is formed. In a tree, the part con- taining intergrown knots comprises a cylinder, extending the entire length of the tree; the part containing loose knots forms a hollow cylinder, extending from the ground to the base of the green crown. Clear wood con- stitutes an outer cylinder covering overgrown branch ends. In second-growth trees, the clear zone and even the zone of loose knots may be absent.

GROWTH RINGS Between the bark and the wood is a layer of thin-walled living cells called the cambium, M 80729 F invisible without a microscope, in which Figure 2-2.—Cross section of a ponderosa pine log showing most growth in thickness of bark and wood growtli rings: Light bands are earlywood, darl< bands are late- arises by cell division. No growth in either wood. An annual ring is composed of the earlywood ring and diameter or length takes place in wood al- the latewood ring outside it. ready formed; new growth is purely the ad- dition of new cells, not the further develop- Growth rings are most readily seen in species ment of old ones. New wood cells are formed with sharp contrast between earlywood and on the inside and new bark cells on the out- latewood, such as the native ring-porous hard- side of the cambium. As the diameter of the woods as ash and oak, and most softwoods woody trunk increases, the bark is pushed out- except the soft pines. In some other species, ward, and the outer bark layers become such as water túpelo, sweetgum, and soft stretched, cracked, and ridged in patterns often maple, differentiation of early and late characteristic of a species. A bark cambium growth is slight, and the annual growth rings forms from living cells and this tissue sepa- are difficult to recognize. In some tropical rates the outer bark from the inner bark. regions, growth may be practically continuous With most species in temperate climates, throughout the year, and no well-defined there is sufficient difference between the wood annual rings are formed.

2-3 EARLYWOOD AND LATEWOOD and physically, from the cells of the inner sap- wood rings. In this condition these cells cease The inner part of the growth ring formed to conduct sap. first in the growing season is called earlywood or springwood, and the outer part formed The cell cavities of heartwood also may later in the growing season, latewood or sum- contain deposits of various materials which merwood. Actual time of formation of these frequently give much darker color to the heart- two parts of a ring may vary with environ- wood. All heartwood, however, is not dark mental and weather conditions. Earlywood is colored. Species in which heartwood does not characterized by cells having relatively large darken to a great extent include the spruces cavities and thin walls. Latewood cells have (except Sitka spruce), hemlock, the true smaller cavities and thicker walls. The transi- firs, Port-Orford-cedar, basswood, cottonwood, tion from earlywood to latewood may be grad- and buckeye. The infiltrations or materials de- ual or abrupt, depending on the kind of wood posited in the cells of heartwood usually make and the growing conditions at the time it was the wood more durable when used in exposed situations. Unless treated, all sapwood is non- formed. In some species, such as the maples, durable when exposed to conditions that favor gums, and yellow-poplar, there is little differ- decay. ence in the appearance of the earlywood and latewood parts of a growth ring. In some species, such as the ashes, hickories, When growth rings are prominent, as in and certain oaks, the pores become plugged to most softwoods and the ring-porous hard- a greater or lesser degree with ingrowths, woods, earlywood differs markedly from late- known as tyloses, before the change to heart- wood in physical properties. Earlywood is light- wood is completed. Heartwood having pores tightly plugged by tyloses, as in white oak, is er in weight, softer, and weaker than latewood ; suitable for tight cooperage. it shrinks less across and more lengthwise along the grain of the wood. Because of the greater Heartwood has a higher extractives content density of latewood, the proportion of late- than sapwood, and because of this, exhibits a wood is sometimes used to judge the quality higher specific gravity. For most species the or strength of wood. This method is useful difference is so small as to be quite unimpor- with such species as the southern pines, tant. The weight and strength of wood are Douglas-ñr, and the ring-porous hardwoods- influenced more by growth conditions of the ash, hickory, and oak. trees at the time the wood is formed than they are by the change from sapwood to heartwood. In some instances, as in redwood, western red- SAPWOOD AND HEARTWOOD cedar, and black locust, considerable amounts of infiltrated material may somewhat increase Sapwood is located next to the cambium. It the weight of the wood and its resistance to contains only a few living cells and functions crushing. primarily in the storage of food and the mechanical transport of sap. WOOD CELLS The sapwood layer may vary in thickness and in the number of growth rings contained Wood cells that make up the structural ele- in it. Sapwood commonly ranges from II/2 to 2 ments of wood are of various sizes and shapes inches in radial thickness. In certain species, and are quite firmly grown together. Dry wood such as catalpa and black locust, the sapwood cells may be empty or partly filled with de- contains very few growth rings and some- posits, such as gums and , or with tyloses. times does not exceed one-half inch in thickness. A majority of cells are considerably elongated The maples, hickories, ashes, some of the and pointed at the ends; they are customarily southern pines, and ponderosa pine may have called fibers or tracheids. The length of wood sapwood 3 to 6 inches or more in thickness, fibers is highly variable within a tree and especially in second-growth trees. As a rule, the among species. Hardwood fibers average about more vigorously growing trees of a species have one twenty-fifth of an inch in length (1 mm.) ; softwood fibers (called tracheids) range from wider sapwood layers. Many second-growth one-eighth to one-third of an inch in length trees of merchantable size consist mostly of (3 to 8 mm.). sapwood. In addition to their fibers, hardwoods have Heartwood consists of inactive cells that cells of relatively large diameter known as have been slightly changed, both chemically vessels. These form the main arteries in the

2-4 movement of sap. Softwoods do not contain To the paper industry, lignin is difficult to special vessels for conducting sap longitudinally solubilize and is a sometimes troublesome by- in the tree; this function is performed by the product. Theoretically, it might be converted tracheids. to a variety of chemical products but, practi- Both hardwoods and softwoods have cells cally, a large percentage of the lignin removed (usually grouped into structures) that are from wood during pulping operations is burned oriented horizontally in the direction from for heat and recovery of pulping chemicals. the pith toward the bark. These structures con- One sizable commercial use for lignin is in the duct sap radially across the grain and are formulation of muds, used in the - called rays or wood rays. The rays are most ing of oil wells, where its dispersant and metal- easily seen on quartersawed surfaces. They combining properties are valuable. It has vary greatly in size in different species. In oaks found use also in rubber compounding and as and sycamores, the rays are conspicuous and an air-entraining agent in concrete mixes. add to the decorative features of the wood. Lesser amounts are processed to yield vanillin Wood also has other cells, known as longi- for flavoring purposes and to product solvents tudinal, or axial, parenchyma cells, that func- such as dimethyl sulfide and dimethyl sulfoxide. tion mainly for the storage of food. The are intimately associated with cellulose in nature and, like cellulose, are CHEMICAL COMPOSITION OF WOOD polymeric units built up from simple sugar moleclues. Unlike cellulose, however, the hemi- Dry wood is made up chiefly of the follow- yield more than one type of sugar on ing substances, listed in decreasing order of acid cleavage. Also, the relative amounts of amounts present: Cellulose, lignin, hemicellu- these sugars vary markedly with species. Hard- loses, extractives, and ash-forming minerals. woods contain an average of 20 to 30 percent Cellulose, the major constituent, comprises hemicelluloses with xylose as the major sugar. approximately 50 percent of wood substance by Lesser amounts of arabinose, mannose, and a weight. It is a high-molecular weight linear sugar acid are also attached to the main poly- polymer that, on chemical degradation by mer chain. Softwoods contain an average of 15 mineral acids, yields the simple sugar glucose to 20 percent hemicelluloses, with mannose as as the sole product. During growth of the tree, the main sugar unit. Xylose, arabinose, and the the linear cellulose molecules are arranged into sugar acid are again present at lower levels. highly ordered strands called fibrils, which in The hemicelluloses play an important role in turn are organized into the larger structural fiber-to-fiber bonding in the papermaking elements comprising the cell wall of wood process. The component sugars of hemicellu- fibers. The intimate physical, and perhaps lose 9 re of potential interest for conversion into partially chemical, association of cellulose with chemical products. lignin and the hemicelluloses imparts to wood Unlike the major constituents just discussed, its useful physical properties. Delignified wood the extractives are not part of the wood fibers have great commercial value when re- structure. However, they do contribute to such constituted into paper. Moreover, they may be properties of wood as color, odor, taste, decay chemically altered to form synthetic textiles, resistance, strength, density, hygroscopicity, films, lacquers, and explosives. and flammability. They include and Lignin comprises 23 to 33 percent of soft- other poly-phenolics, coloring matters, essen- woods, but only 16 to 25 percent of hardwoods. tial oils, fats, resins, , gums, starch, and It occurs in the wood largely as an intercellular simple metabolic intermediates. They can be material. Like cellulose, it has a macromole- removed from wood by extraction with such cular chemical structure, but its three- inert neutral solvents as water, alcohol, acetone, dimensional network is far more complex and benzene, and ether. In quantity, the extrac- not yet completely worked out. As a chemical, tives may range from roughly 5 to 30 percent, lignin is an intractable, insoluble material, probably bonded at least loosely to the cellu- depending on such factors as species, growth lose. To remove it from the wood on a commer- conditions, and time of year the tree is cut. cial scale requires vigorous reagents, high Ash-forming minerals comprise from 0.1 to temperatures, and high pressures. Such condi- 3 percent of wood substance, although consid- tions greatly modify the lignin molecule, pro- erably higher values are occasionally reported. ducing a complex mixture of high-molecular- Calcium, potassium, phosphate, and silica are weight phenolic compounds. common constituents. Due to the uniform dis- 2-5 tribution of these inorganic materials through- BIBLIOGRAPHY out the wood, ash often retains the micro- structural pattern of wood. Bratt, L. C. A significant dollar value of nonfibrous prod- 1965. Trends in the production of silvichemicals in the United States and abroad. Tappi ucts is produced from wood including naval 48(7): 46A-49A. Tech. Assoc. Pulp and stores, pulp byproducts, vanillin, ethyl alcohol, Paper Indus. charcoal, extractives, and bark products. Brauns, F. E., and Brauns, D. A. 1960. The chemistry of lignin—supplement vol- IDENTIFICATION ume, 804 pp. Academic Press. Browning, B. L. Many species of wood have unique physical, 1963. The chemistry of wood. 689 pp. Interscience mechanical, or chemical properties. Efficient Publishers, N.Y. utilization dictates that species should be Freudenberg, K. matched to use requirements through an under- 1965. Lignin : Its constitution and formation from p-hydroxy-cinnamyl alcohols. Sei. 148: standing of properties. This requires identi- 595-600. fication of the species in wood form, indepen- Hamilton, J. K., and Thompson, N. S. dent of bark, foliage, and other characteristics 1959. A comparison of the carbohydrates of hard- of the tree. woods and softwoods. Tappi 42: 752-760. Field identification can often be made on the Tech. Assoc. Pulp and Paper Indus. basis of readily visible characteristics such Ott, E., Spurlin, H. M., and Grafflin, M. W. as color, presence of pitch, or grain pattern. 1954. Cellulose and cellulose derivatives. Volume V. Parts I, II, and III (1955) of High Sometimes odor, density, or splitting tendency Polymers. 1601 pp. Interscience Publishers, is helpful. Where more positive identification is N.Y. required, a laboratory investigation of the Panshin, A. J., and de Zeeuw, C. microscopic anatomy of the wood can be made. 1970. Textbook of wood technology. Volume 1. 3d Detailed descriptions of identifying character- edition. McGraw-Hill. istics are given in texts such as "Textbook of Wise, L. E., and Jahn, E. C. 1952. Wood chemistry. Volumes I and II, 1259 pp. Wood Technology" by Panshin and de Zeeuw. Reinhold.

2-6 FS-.353

Chapter 3

PHYSICAL PROPERTIES OF WOOD

Appearance _ 3-2 Grain and Texture 3-2 Plainsawed and Quartersawed Lumber 3-2 Decorative Features of Common Woods 3-3 Moisture Content 3-3 Green Wood and the Fiber Saturation Point __ 3-6 Equilibrium Moisture Content 3-7 Shrinkage . 3-7 Transverse and Volumetric Shrinkage 3-7 Longitudinal Shrinkage 3-7 Moisture-Shrinkage Relationship 3-11 Density-Specific Gravity-Weight __ _ 3-12 Working Qualities ^ _ _ _. 3-15 Weathering 3_16 Decay Resistance „ 3-16 Chemical Resistance 3-17 Thermal Properties 3-19 Thermal Conductivity 3-19 Specific Heat 3-19 Thermal Diifusivity 3-21 Coefficient of Thermal Expansion 3-21 Electrical Properties __ 3-21 Electrical Conductivity 3-22 Dielectric Constant 3-22 Dielectric Power Factor 3-22 Coefficient of Friction 3-23 Nuclear Radiation 3-23 Bibliography 3-.24

3-1 PHYSICAL PROPERTIES OF WOOD

The versatility of wood is demonstrated by producing "plainsawed" lumber in hardwoods a wide variety of products. This variety is a re- and "flat-grained" or "slash-grained" lumber sult of a spectrum of desirable physical char- in softwoods; and radially to the rings or paral- acteristics or properties that is available among lel to the rays, producing "quartersawed" the many species of wood. Often more than lumber in hardwoods and "edge-grained" or one property of wood is important to an end "vertical-grained" lumber in softwoods (fig. product. For example, to select a species for a 3-1). Usually quartersawed or edge-grained product, the value of appearance-type prop- lumber is not cut strictly parallel with the erties such as texture, grain pattern, or color rays; and often in plainsawed boards the sur- may be evaluated against the influence of char- faces next to the edges are far from being tan- acteristics such as machinability, stability, or gent to the rings. In commercial practice, decay resistance. This chapter discusses the lumber with rings at angles of 45° to 90° physical properties most often of interest in with the wide surface is called quartersawed, the design of wood products. and lumber with rings at angles of 0° to 45° Some physical properties discussed and with the wide surface is called plainsawed. tabulated are influenced by species as well as Hardwood lumber in which annual rings make variables like moisture content; other proper- angles of 30° to 60° with the wide faces is ties tend to be more independent of species. sometimes called "bastard sawn." The thoroughness of sampling and the degree of variability influences the confidence with which species-dependent properties are known. In this chapter an effort is made to indicate either the general or specific nature of the prop- erties tabulated.

APPEARANCE

Grain and Texture The terms "grain" and "texture" are com- monly used rather loosely in connection with wood. Grain is often used in reference to an- nual rings, as in fine grain and coarse grain, but it is also employed to indicate the direc- tion of fibers, as in straight grain, spiral grain, and curly grain. Grain, as a synonym for fiber direction, is discussed in more detail relative to mechanical properties in chapter 4. Wood finishers refer to woods as open grained and close grained as terms reflecting the rela- tive size of the pores, which determines whether the surface needs a . Texture is often used synonymously with grain, but us- ually it refers to the finer structure of wood rather than to annual rings. When the words B

"grain" or "texture" are used in connection ZM 554 F with wood, the meaning intended should be Figure 3-1.—Quartersawed A and plainsawed B boards cut from made perfectly clear (see glossary). o log. For many purposes either plainsawed or Plainsawed and Quartersawed Lumber quartersawed lumber is satisfactory. Each type has certain advantages, however, that may Lumber can be cut from a log in two by important in a particular use. Some of the distinct ways: Tangent to the annual rings. advantages are given in table 3-1.

3-2 Table 3-1—Some advantages of pMnsawed and the annual growth rings frequently form quartersawed lumber ellipses and parabolas that make striking figures, especially when the rings are irregular Plainsawed Quartersawed in width and outline on the cut surface. On quartersawed surfaces, these rings form Figure patterns resulting Quartersawed lumber from the annual rings shrinks and swells less stripes, which are not especially ornamental and some other types of in width. unless they are irregular in width and direc- figure are brought out tion. The relatively large rays, sometimes re- more conspicuously by It twists and cups less. plainsawing. ferred to as necks, form a conspicuous figure It surface-checks and in quartersawed oak and sycamore. With inter- Round or oval knots that splits less in seasoning locked grain, which slopes in alternate direc- may occur in plainsawed and in use. boards affect the surface tions in successive layers from the center of appearance less than Raised grain caused by the tree outward, quartersawed surfaces show spike knots that may separation in the annual occur in quartersawed rings does not become so a ribbon effect, either because of the difference boards. pronounced. in reflection of light from successive layers Also, a board with a when the wood has a natural luster or because round or oval knot is It wears more evenly. not as weak as a board cross grain of varying degree absorbs stains with a spike knot. Types of figure due to pro- unevenly. Much of this type of figure is lost nounced rays, inter- in plainsawed lumber. Shakes and pitch pockets, locked grain, and wavy when present, extend grain are brought out In open-grained hardwoods, the appearance through fewer boards. more conspicuously. of both plainsawed and quartersawed lumber can be varied greatly by the use of fillers of It is less susceptible to It does not allow liquids to collapse in drying. pass into or through it different colors. In softwoods, the annual so readily in some spe- growth layers can be made to stand out more It shrinks and swells less cies. by applying a stain. in thickness. It holds paint better in Knots, pin wormholes, bird pecks, decay in It may cost less because some species. isolated pockets, birdseye, mineral streaks, it is easier to obtain. The sapwood appearing in swirls in grain, and ingrown bark are decora- boards is at the edges tive in some species when the wood is care- and its width is limited fully selected for a particular architectural according to the width of the sapwood in the treatment. log. MOISTURE CONTENT Moisture content of wood is defined as the Decoraffve Features of Common Woods weight of water in wood expressed as a frac- tion, usually as a percentage, of the weight The decorative value of wood depends upon of ovendry wood. Weight, shrinkage, strength, its color, figure, luster, and the way in which and other properties depend upon moisture con- it bleaches or takes fillers, stains, and trans- tent of wood. parent finishes. Because of the combinations In trees, moisture content may range from of color and the multiplicity of shades about 30 percent to more than 200 percent of found in wood, it is impossible to give detailed the weight of wood substance. Moisture con- descriptions of colors of the various kinds. Sap- wood of most species, however, is light in tent of the sapwood portion is usually high. color, and in some species it is practically Heartwood moisture content may be much white. White sapwood of certain species, such less than sapwood moisture content in some as maple, may be preferred to the heartwood species, greater in others. Table 3-3 gives for specific uses. In some species, such as hem- some moisture content values for heartwood lock, spruce, the true firs, basswood, cotton- and sapwood of some domestic species. These wood, and beech, there is typically little or no values are considered typical, but there is con- difference in color between sapwood and heart- siderable variation within and between trees. wood, but in most species heartwood is darker Variability of moisture content exists even and fairly uniform in color. Table 3-2 describes within individual boards cut from the same in a general way the color of heartwood of tree. Information on heartwood and sapwood the more common kinds of woods. moisture content is not available for imported In plainsawed boards and rotary-cut veneer. species.

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3-4 3-5 Table 3-3.—Average moisture content of green wood, by species

Moisture content ^ Moisture content ^ Species Heart- Sap- Species Heart- Sap- wood wood wood wood Pet. Pet. Pet. Pet. ~" HARDWOODS SOFTWOODS Alder, red 97 Baldcypress 121 171 Apple 8Í 74 Cedar : Asn: Alaska- 32 166 Black 95 Eastern redcedar 33 Green _ _ ~ 53 Incense- 40 2Í3 White 46 44 Port Orford- 50 98 Aspen 95 113 Western redcedar 58 249 Basswood, American _ 81 133 Douglas-fir : Beech, American 55 72 Coast type 37 115 Birch : Fir: Paper 89 72 Grand 91 136 Sweet 75 70 Noble 34 115 Yellow 74 72 Pacific silver _ 55 i64 Cherry, black 58 White 98 160 Chestnut, American 120 Hemlock : Cottonwood, black 162 146 Eastern 97 119 Elm: Western 85 170 American 95 92 Larch, western 54 no Cedar QQ 61 Pine: Rock 44 57 Loblolly 33 no Hackberry 61 65 Lodgepole 41 120 Hickory, pecan : Longleaf 31 106 Bitternut 80 54 Ponderosa 40 148 Water 97 62 Red 32 134 Hickory, true : Shortleaf 32 122 Mockernut 70 52 Sugar 98 219 Pigiiut 71 49 Western white 62 148 Bed 69 52 Redwood, old-growth 86 210 Sand 68 50 Spruce: Magnolia 80 104 Eastern 34 128 Maple : Engelmann 51 173 Silver „ _ 58 97 Sitka 41 142 Sugar _ 65 72 Tamarack 49 Oak: California black 76 75 * Based on weight when ovendry. Northern red 80 69 Southern red 83 75 Water 81 81 White _ 64 78 Willow - _ 82 74 Sweetgum 79 137 Sycamore, American _ 114 130 Tupelo: Black _ _ 87 115 Swamp 101 108 Water 150 UQ Walnut, black 90 73 Yellow-poplar 83 106

Green Wood and Fiber Saturation Point Moisture can exist in wood as water or tion point." The fiber saturation point of wood water vapor in cell lumens (cavities) and as averages about 30 percent moisture content, but water "bound" chemically within cell walls. individual species and individual pieces of wood Green wood often is defined as wood in which may vary by several percentage points from the cell walls are completely saturated with that value. water; however, green wood usually contains The fiber saturation point often also is con- additional water in the lumens. The moisture sidered as that moisture content below which content at which cell walls are completely the physical and mechanical properties of wood saturated (all "bound" water) but no water begin to change as a function of moisture con- exists in cell cavities is called the "fiber satura- tent.

3-6 EquíUbrium Moisture Content (radially), and only slightly along the grain The moisture content of wood below the (longitudinally). The combined effects of radial fiber saturation point or "green" condition is and tangential shrinkage can distort the shape a function of both relative humidity and tem- of wood pieces because of the difference in perature of the surrounding air. The equilib- shrinkage and the curvature of annual rings. Figure 3-2 illustrates the major types of dis- rium moisture content is defined as that tortion due to these effects. moisture content at which the wood is neither gaining nor losing moisture; an equilibrium condition has been reached. The relationship Transverse and Volumetric Stirinlcage between equilibrium moisture content, relative Data have been collected to represent the humidity, and temperature is shown in table average radial, tangential, and volumetric 3-4. This table illustrates that below the fiber shrinkage of numerous domestic species by saturation point wood will attain a moisture methods described in ASTM Designation D143. content in equilibrium with widely diflfering These shrinkage values, expressed as a atmospheric conditions. For most practical percentage of the green dimension, are sum- purposes the values in table 3-4 may be ap- marized in table 3-5. Shrinkage values col- plied to wood of any species. lected from the world literature for selected Wood in service usually is exposed to both imported species are summarized in table 3-6. long-term (seasonal) and short-term (such as The shrinkage of wood is affected by a daily) changes in the relative humidity and number of variables. In general, greater temperature of the surrounding air. Thus, shrinkage is associated with greater density. wood virtually always is undergoing at least The size and shape of a piece of wood may slight changes in moisture content. These also affect shrinkage, as may the temperature changes usually are gradual and short-term and rate of drying for some species. Trans- fluctuations tend to influence only the wood verse and volumetric shrinkage variability can surface. Moisture content changes may be re- be expressed by a coefficient of variation of tarded by protective coatings, such as , approximately 15 percent, based on a study , or paint. The practical objective of in which 50 species were represented. all wood seasoning, handling, and storing meth- ods should be to minimize moisture content Longitudinal Shrinkage changes in wood in service. Favored procedures are those that bring the wood to a moisture Longitudinal shrinkage of wood (shrinkage content corresponding to the average atmos- parallel to the grain) is generally quite small. pheric conditions to which it will be exposed Average values for green to ovendry shrink- (see ch. 14 and 16). age are between 0.1 and 0.2 percent for most species of wood. Certain atypical types of SHRINKAGE wood, however, exhibit excessive longitudinal shrinkage, and these should be avoided in uses Wood is dimensionally stable when the mois- where longitudinal stability is important. Re- ture content is above the fiber saturation point. action wood, whether compression wood in Wood changes dimension as it gains or loses softwoods or tension wood in hardwoods, tends moisture below that point. It shrinks when to shrink excessively along the grain. Wood losing moisture from the cell walls and swells from near the center of trees (juvenile wood) when gaining moisture in the cell walls. This of some species also shrinks excessively length- shrinking and swelling may result in warping, wise. Wood with cross grain exhibits increased checking, splitting, or performance problems shrinkage along the longitudinal axis of the that detract from its usefulness. It is there- piece. fore important that these phenomena be un- Reaction wood exhibiting excessive longi- derstood and considered when they may affect tudinal shrinkage may occur in the same board a product in which wood is used. with normal wood. The presence of this type Wood is an anisotropic material in shrink- of wood, as well as cross grain, can cause age characteristics. It shrinks most in the di- serious warping such as bow, crook, or twist, rection of the annual growth rings (tangen- and cross breaks may develop in the zones of tially), about one-half as much across the rings high shrinkage.

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3-8 Table 3-5.—Shrinkage values of domestic woods

Shrinkage from green to Shrinkage from green to ovendry moisture content ^ ovendry moisture content ' Species Species Radial Tangential Volumetric Radial Tangential Volumetric PcL Pet, Pet. Pet. Pet. Pet. HARDWOODS

Alder, red 4.4 7.3 12.6 Ash; Honeylocust 4.2 6.6 10.8 Black 6.0 Locust, black 4.6 7.2 10.2 7.8 15.2 Madrone, Pacific . 5.6 12.4 18.1 Blue 3.9 6.5 11.7 Magnolia : Green 4.6 7.1 12.5 Cucumbertree _ 5.2 8.8 13.6 Oregon 4.1 8.1 18.2 Southern 5.4 ^,Q Pumpkin 3.7 12.3 6.3 12.0 Sweetbay 4.7 8.3 12.9 White 4.9 7.8 13.3 Maple: Aspen : Bigleaf 3.7 7.1 Bigtooth 3.3 11.6 7.9 11.8 Black 4.8 9.3 14.0 Quaking 3.5 6.7 11.5 Red --_ 4.0 8.2 Basswood, 12.6 Silver 3.0 7.2 12.0 American 6.6 15.8 Striped 3.2 8.6 Beech, American _ 5.5 12.8 11.9 17.2 Sugar 4.8 9.9 14.7 Birch: Oak, red : Alaska paper __ 6.5 9.9 16.7 Gray 5.2 Black 4.4 11.1 15.1 14.7 Laurel 4.0 9.9 19.0 Paper 6.3 "8.6 16.2 River 4.7 Northern red __ 4.0 8.6 13.7 9.2 13.5 Pin ._ 4.3 9.5 14.5 Sweet 6.5 9.0 15.6 Yellow 7.3 Scarlet 4.4 10.8 14.7 9.5 16.8 Southern red __ 4.7 11.3 16.1 Buckeye, yellow _- 3.6 8.1 12.5 Butternut 3.4 Water 4.4 9.8 16.1 6.4 10.6 Willow 5.0 9.6 18.9 Cherry, black 3.7 7.1 11.5 Oak, white : Chestnut, Bur 4.4 8.8 12.7 American 3.4 6.7 11.6 Chestnut 5.3 10.8 16.4 Cottonwood : Live , 6.6 9.5 14.7 Balsam poplar _ 3.0 7.1 10.5 Overcup 5,3 12.7 16.0 Black 3.6 8.6 12.4 Post 5.4 9.8 16.2 Eastern 3.9 9.2 13.9 Swamp Elm: chestnut 5.2 10.8 16.4 American 4.2 7.2 14.6 White 5.6 10.5 16.3 Cedar 4.7 10.2 15.4 Persimmon, Rock 4.8 8.1 14.9 common 7.9 11.2 19.1 Slippery 4.9 8.9 13.8 Sassafras 4.0 6.2 10.3 Winged 5.3 11.6 17.7 Sweetgum 5.3 10.2 15.8 Hackberry 4.8 Sycamore, 8.9 13.8 American 5.0 8.4 Hickory, Pecan _ _ 4.9 8.9 13.6 14.1 Hickory, True : Tanoak 4.9 11.7 17.3 Tupelo: Mockemut 7.7 11.0 17.8 Black 5.1 8.7 Pignut 7.2 14.4 11.5 17.9 Water 4.2 7.6 12.5 Shagbark 7.0 10.5 16.7 Walnut, black __. 5.5 7.8 12.8 Shellbark 7.6 12.6 19.2 Willow, black 3.3 8.7 13.9 Holly, American _ 4.8 9.9 16.9 Yellow-poplar __- 4.6 8.2 12.7

SOFTWOODS

Baldcypress 3.8 6.2 10.5 Fir: Cedar : Balsam 2.9 6.9 11.2 Alaska- 2.8 6.0 9.2 California red 4.5 7.9 11.4 Atlantic white- 2.9 5.4 8.8 Grand 3.4 7.5 11.0 Eastern Noble 4.3 8.3 12.4 redcedar 3.1 4.7 7.8 Pacific silver _ _ 4.4 9.2 13.0 Incense- 3.3 5.2 7.7 Subalpine 2.6 7.4 9 4 Northern White 3.3 7.0 9.8 white- 2.2 4.9 7.2 Hemlock : Port-Orford- _ 4.6 6.9 10.1 Eastern 3.0 6.8 9.7 Western Mountain 4.4 7.1 ii.i redcedar 2.4 5.0 6.8 Western 4.2 7.8 12.4 Douglas-fir : ^ Larch, western __ 4.5 9.1 14 0 Coast 4.8 7.6 12.4 Pine: Interior north 3.8 6.9 10.7 Eastern white _ 2.1 6.1 8.2 Interior west __ 4.8 7.5 11.8 Jack 3.7 6.6 10.3 3-9 Table 3-5.—Shrinkage values of domestic woods—continued

Shrinkage from green to Shrinkage from green to ovendry moisture content ^ ovendry moisture content ^ Species Species Radial Tangential Volumetric Radial Tangential Volumetric PcL Pet. Pet. Pet Pet. Pet. SOFTWOODS—Continued

Pine (cont.) Spruce: Loblolly 4.8 7.4 12.3 Black 4.1 6.8 11.3 Lodgepole 4.3 6.7 11.1 Engelmann __ 3.8 7.1 11.0 Longleaf 5.1 7.5 12.2 Red 3.8 7.8 11.8 Pitch 4.0 7.1 10.9 Sitka 4.3 7.5 11.5 Pond 5.1 7.1 11.2 Tamarack 3.7 7^4 13.6 Ponderosa 3.9 6.2 9.7 Red 3.8 7.2 11.3 ' Expressed as a percentage of the green dimension. Shortleaf 4.6 7.7 12.3 ^ Coast Douglas-fir is defined as Douglas-fir growing Slash 5.4 7.6 12.1 in the States of Oregon and Washington west of the Sugar 2.9 5.6 7.9 summit of the Cascade Mountains. Interior West in- Virginia 4.2 7.2 11.9 cludes the State of California and all counties in Western white _ 4.1 7.4 11.8 Oregon and Washington east of but adjacent to the Redwood : Cascade summit. Interior North includes the remainder Old-growth ___- 2.6 4.4 6.8 of Oregon and Washington and the States of Idaho, Young-growth 2.2 4.9 7.0 Montana, and Wyoming.

ZM f2494 F Figure 3-2.—Characteristic shrinlcage and distortion of flats, squares, and rounds as affected by the direction of the annual rings. Tangential shrinkage is about twice as great as radial. 3-10 curve depends on several variables, principally size and shape of the piece, species of wood, and drying conditions employed. Considerable variation in shrinkage occurs for any species. Figure 3-3 is a plot of shrink- age data for boards, Vs by 5^/^ inches in cross section, of Douglas-fir from one locality when dried under mild conditions from green to near equilibrium at 65° F. and 30 percent rel- ative humidity. The figure shows that it is impossible to predict accurately the shrinkage of an individual piece of wood; the average shrinkage of a quantity of pieces is more pre- 6 8 10 12 14 16 20 22 MOISTURE CONTENT (PERCENT) dictable. If the shrinkage-moisture content relation- M I40 413 ship is not known for a particular product and Figure 3-3.—An illustration of variation in individual tangential drying condition, the data in tables 3-5 and shrinkage values of several boards of Douglas-fir from one locality, dried from green condition. 3-6 can be used to estimate shrinkage from the green condition to any moisture content: lÁo\%\\3T^'%hrmkQQ^ Relationship _ Ç / 30-m\ The shrinkage of a small piece of wood normally begins at about the fiber saturation where Sm is shrinkage (in percent) from the point and continues in a fairly linear manner green condition to moisture content m (below until the wood is completely dry. However, in 30 pet.) and So is total shrinkage (in percent) the normal drying of lumber or other large from table 3-5 or 3-6. If the moisture content pieces of wood the surface of the wood dries at which shrinkage from the green condition first. When the surface gets below the fiber begins is known to vary from 30 percent for saturation point, it begins to shrink. Mean- a species, the shrinkage estimate can be im- while, the interior may still be quite wet. The proved by replacing 30 in the equation with exact form of the moisture content-shrinkage the appropriate moisture content.

TABLE 3-6.—Shrinkage for some woods imported into the United States

Shrinkage from Shrinkage from green to ovendry green to ovendry moisture content ^ moisture content ^ Species Species Radial Tangential Radial Tangential Pet. Pet Pet Pet Andiroba (Carapa Mahogany (Swietenia guianensis) 4.0 7.8 macrophylla) 3.7 5.1 Angélique (Dicorynia Nogal (Juglans spp.) 2.8 5.5 guianensis) 5.2 8.8 Obeche (Triplochiton Apitong (Dipterocarpus scleroxylon) 3.1 5.3 spp.) 5.2 10.9 Okoume (Awcoumea Avodire (Turraeanthus klaineanv) . 5.6 6.1 africanus) 3.7 6.5 Parana pine (Araucaria Balsa (Ochroma angustifolia) 4.0 7.9 pyramidale) 3.0 7.6 Primavera (Cybistax donnell- Banak (Virola smithii) 3.1 5.2 surínamensis) . 4.6 8.8 Ramin (Gonystylus spp.) 3.9 8.7 Cativo (Prioria Santa Maria (Calophyllum copaifera) 2.3 5.3 brasiliense) 5.4 7.9 Greenheart (Ocotea Spanish-cedar (Cedrela spp.) 4.1 6.3 rodiaei) 8.2 9.0 Teak (Tectona grandis) 2.2 4.0 Ishpingo (Amburana Virola (Dialyanthera spp.) _ 5.3 9.6 acreana) 2.7 4.4 Walnut, European (Juglans Khaya (Khaya spp.) 4.1 5.8 regia) 4.3 6.4 Kokrodua (Pericopsis elata) 3.2 6.3 Lauan (Shorea spp.) 3.8 8.0 * Shrinkage values in this table were obtained from Limba (Terminalia world literature and may not represent a true species superha) 4.4 5.4 average. Lupuna (Ceiba samauma) 3.5 6.3 ^ Expressed as a percentage of the green dimension. 3-11 So may be an appropriate value of radial, To standardize comparisons of species or tangential, or volumetric shrinkage.. Tangen- products and estimations of product weights, tial values should be used for estimating v^idth specific gravity is used as a standard refer- shrinkage of flat-sawed material; radial values ence basis, rather than density. The tradi- for quartersawed material. For mixed or un- tional definition of specific gravity is the ratio known ring orientations, the tangential values of the density of the wood to the density of are suggested. Individual pieces will vary from water at a specified reference temperature predicted shrinkage values. As noted pre- (often 4° C. where the density of water is viously, shrinkage variability is characterized 1.0000 g. per cc). To reduce any confusion by a coefficient of variation of approximately introduced by the variable moisture content 15 percent. Chapter 14 contains further dis- the specific gravity of wood usually is based cussion of shrinkage-moisture content rela- on the ovendry weight and the volume at some tions. specified moisture content. A coeflSicient of variation of about 10 percent describes the variability inherent in many common domestic DENSITY-SPECIFIC GRAVITY-WEIGHT species. In research activities specific gravity may Two primary sources of variation affect the be reported on the basis of both weight and weight of wood products. One is the density volume ovendry. For engineering work, the of the basic wood structure; the other is the basis commonly is ovendry weight and volume variable moisture content. A third source, at the moisture content of test or use. Often minerals and extractable substances, has a the moisture content of use is taken as 12 marked effect only on a limited number of percent. Some specific gravity data are re- species. The density of wood, exclusive of ported in table 4-2, chapter 4, on this basis. water, varies greatly both within and between If the specific gravity of wood is known, species. While the density of most species based on ovendry weight and volume at a falls between about 20 and 45 pounds-mass per specified moisture content, the specific gravity cubic foot, the range of densities actually ex- at any other moisture content between 0 and tends from about 10 pounds-mass per cubic 30 percent can be approximated from figure foot for balsa to over 65 pounds-mass per 3-4. This figure adjusts for average shrinkage cubic foot for some other imported woods. A and swelling that affects the volume of the coefficient of variation of about 10 percent is wood. The specific gravity of wood based on considered suitable for describing the varia- ovendry weight does not change at moisture bility of density within common domestic spe- contents above approximately 30 percent (the cies. approximate fiber saturation point). To use Wood is used in a wide range of conditions figure 3--4 locate the point corresponding to and thus has a wide range of moisture con- the known specific gravity on the vertical axis tents in use. Since moisture makes up part of and the specified moisture content on the hori- the weight of each product in use, the density zontal axis. From this point, move left or must reflect this fact. This has resulted in right parallel to the inclined lines until verti- the density of wood often being determined cally above the target moisture content. Then and reported on a moisture content-in-use con- read the new specific gravity corresponding dition. to this point at the left-hand side of the graph. The calculated density of wood, including With a knowledge of the specific gravity at the water contained in it, is usually based on the moisture content of interest, the density of average species characteristics. This value wood including water at that moisture content should always be considered an approximation can be read directly from table 3-7. ^ For because of the natural variation in anatomy, example, to estimate the density of white ash moisture content, and the ratio of heartwood at 12 percent moisture content, consult table to sapwood that occurs. Nevertheless, this de- 4-2 in chapter 4. The average green specific termination of density usually is sufficiently gravity for the species is 0.55. Using figure accurate to permit proper utilization of wood 3-4, the 0.55 green specific gravity curve is products where weight is important. Such ap- found to intersect with the vertical 12 percent plications range from estimation of structural moisture content line at a point corresponding loads to the calculating of approximate ship- ' Table 3-7 is repeated as A-3-7 in metric (SI) units ping weights. at the end of this chapter. 3-12 1 1 1 1 I n 1 \ \ r 1 1 1 1 0.80 A^ — SPECIFIC GRAVITY ^ m / tAJC lÀ/UCAt />OCCAi 0,76 (V r \jn L.t^lW 7 - V, ^ ^ — 0,72 "^, V, ■^ — > ^ ^ ^ ^ c N»^ 0,68 ■V,

^ ^ ^ ^ ^ ^ ^ '^c So 0,64 "^ - ^ ^ ^ ^ ^^ 0,60 ^*^ ^c ■Se ^ s ^ - -- ^ 0,56 i \ **ö se ^ --. :: :: si 0,52 - -o.^^ ¡s —- — - ^ - si 0,48 - ■ ^o ^ s ■--- — I — ■— 0.40 ±1 — ;^ — 0.36 — 0,36 -— — — — ^c .32 0,32 —- — — — — i i — 0 2e 0,28 — — — - ^ — 0,24 0,24 — —1 — 0 0.20 20 -t- -t- -f 1 -4+ 4-J-4- -X- z »L 1 o 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 MOISTURE CONTENT (PERCENT) M I40 416 Figure 3^4.—Relation of specific gravity and moisture content.

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Table 3-8.—Some machining and related properties of selected domestic hardwoods

Nail Screw split- split- Mortis- ting- ting— Boring— ing— pieces pieces Kind of wood Í Shaping— Turning— good to fair to Sanding— steam free free Planing— good to fair to excel- excel- good to bending— from from perfect excellent excellent lent lent excellent unbroken complete complete pieces pieces pieces pieces pieces pieces pieces splits splits Pet Pet. Pet Pet Pet Pet Pet Pet Pet Alder red 61 20 88 64 52 Ash 75 55 79 94 58 75 61 65 71 Aspen 26 7 65 78 60 Basswood 64 10 68 76 51 17 2 79 68 Beech _ _ 83 24 90 99 92 49 75 42 58 Birch 63 57 80 97 97 34 72 32 48 Birch, paper 47 22 - Cherry, black 80 80 88 100 100 Chestnut 74 28 87 91 70 64 56 66 60 Cottonwood 21 3 70 70 52 19 44 82 78 Elm, soft 33 13 65 94 75 66 74 80 74 Hackberry 74 10 77 99 72 94 63 63 Hickory 76 20 84 100 98 80 76 35 63 Magnolia 65 á7 79 71 32 37 85 73 76 Maple, bigleaf 52 56 80 100 80 Maple, hard 54 72 82 99 95 38 57 27 52 Maple, soft 41 25 76 80 34 37 59 58 61 Oak, red 91 28 84 99 95 81 86 66 78 Oak, white 87 35 85 95 99 83 91 69 74 Pecan ______88 40 89 100 98 78 47 69 Sweetgum 51 28 86 92 58 23 67 69 69 Sycamore 22 12 85 98 96 21 29 79 74 Tanoak _ 80 39 81 100 100 Tupelo, water 55 52 79 62 33 34 46 64 63 Tupelo, black 48 32 75 82 24 21 42 65 63 Walnut, black 62 34 91 100 98 __ 78 50 59 Willow 52 5 58 71 24 24 73 89 62 Yellow-poplar 70 13 81 87 63 19 58 77 67 ' Commercial lumber nomenclature.

3-15 Table 3-9.—Some characteristics of imported or cracks that are easily visible. Moderate to woods that Tnay effect machining. low density woods acquire fewer checks than do high density woods. Vertical-grain boards Hard mineral Irregular and deposits (silica check less than flat-grain boards. interlocked or calcium Reaction wood As a result of weathering, boards tend to grain carbonate) (tension wood) warp (particularly cup) and pull out their Apamate Angélique Andiroba fastenings. The cupping tendency varies with Apitong Apitong Banak the density, width, and thickness of a board. Avodire Kapur Cativo Capirona Okoume Khaya The greater the density and the greater the Courbaril Palosapis Lupuna width in proportion to the thickness, the Gola Rosewood, Mahogany greater is the tendency to cup. Warping also Goncalo alves Indian Nogal Ishpingo Teak Sande is more pronounced in flat-grain boards than Jarrah Spanish-cedar in vertical-grain boards. For best cup resist- Kapur Karri ance, the width of a board should not exceed Khaya eight times its thickness. Kokrodua Biological attack of a wood surface by micro- Lapacho Laurel organisms is recognized as a contributing fac- Lignum vitae tor to color changes. When weathered wood Limba has an unsightly dark gray and blotchy ap- Meranti Obeche pearance, it is due to dark-colored fungal Okoume spores and mycelium on the wood surface. The Palosapis formation of a clean, light gray, silvery sheen Peroba de campos Primavera on weathered wood occurs most frequently Rosewood, Indian where micro-organism growth is inhibited by Santa Maria Sapele a hot, arid climate or a salt atmosphere in coastal regions. The contact of and other metallic WEATHERING products with the weathering wood surface is a source of color, often undesirable if a na- Without protective treatment, freshly cut tural color is desired. Chapter 16 discusses wood exposed to the weather changes mate- this effect in more detail. rially in color. Other changes due to weather- Details of treatments to preserve the natural ing include warping, loss of some surface color, retard biological attack, or impart ad- fibers, and surface roughening and checking. ditional color to the wood, are covered in The effects of weathering on wood may be chapters 16, 17, and 18. desirable or undesirable, depending on the re- quirements for the particular wood product. The time required to reach the fully weathered DECAY RESISTANCE appearance depends on the severity of the Wood kept constantly dry does not decay. exposure to sun and rain. Once weathered, Further, if it is kept continuously submerged wood remains nearly unaltered in appearance. in water even for long periods of time, it The color of wood is affected very soon on is not decayed significantly by the common exposure to weather. With continued exposure decay fungi regardless of the wood species or all woods turn gray; however, only the wood at or near the exposed surfaces is noticeably the presence of sapwood. and cer- affected. This very thin gray layer is com- tain soft-rot fungi can attack submerged wood posed chiefly of partially degraded cellulose but the resulting deterioration is very slow. fibers and micro-organisms. Further weather- A large proportion of wood in use is kept so ing causes fibers to be lost from the surface dry at all times that it lasts indefinitely. Mois- but the process is so slow that only about % ture and temperature, which vary greatly inch is lost in a century. with local conditions, are the principal factors In the weathering process, chemical de- affecting rate of decay. When exposed to con- gradation is influenced greatly by the wave- ditions that favor decay, wood deteriorates length of light. The most severe effects are more rapidly in warm, humid areas than in produced by exposure to ultraviolet light. As cool or dry areas. High altitudes, as a rule, cycles of wetting and drying take place, most are less favorable to decay than low altitudes woods develop physical changes such as checks because the average temperatures are lower

3-16 and the growing seasons for fungi, which Precise ratings of decay resistance of heart- cause decay, are shorter. wood of different species are not possible be- The heartwoods of some common native cause of differences within species and the species of wood have varying degrees of na- variety of service conditions to which wood is tural decay resistance. Untreated sapwood of exposed. However, broad groupings of many of substantially all species has low resistance to the native species, based on service records, decay and usually has a short service life under laboratory tests, and general experience, are decay-producing conditions. The decay resist- helpful in choosing heartwood for use under ance of heartwood is greatly affected by dif- conditions favorable to decay. Table 3-10 shows ferences in the preservative qualities of the such groupings for some domestic woods, ac- wood extractives, the attacking fungus, and cording to their average heartwood decay re- the conditions of exposure. Considerable dif- sistance, and table 3-11 gives similar group- ference in service life may be obtained from ings for some imported woods. The extent of pieces of wood cut from the same species, or variations in decay resistance of individual even from the same tree, and used under trees or wood samples of a species is much apparently similar conditions. There are greater for most of the more resistant species further complications because, in a few spe- than for the slightly or nonresistant species. cies, such as the spruces and the true firs (not Where decay hazards exist, heartwood of Douglas-fir), heartwood and sapwood are so species in the resistant or very resistant cate- similar in color that they cannot be easily gory generally gives satisfactory service, but distinguished. Marketable sizes of some species heartwood of species in the other two cate- such as southern pine and baldcypress are be- gories will usually require some form of coming largely second growth and contain a preservative treatment. For mild decay condi- high percentage of sapwood. tions, a simple preservative treatment—such as a short soak in preservative after all cut- Table 3-10.—Grouping of some domestic woods ting and boring operations are complete—will according to heartwood decay be adequate for wood low in decay resistance. Resistant or Moderately Slightly or For more severe decay hazards, pressure very resistant resistant nonresistant treatments are often required; even the very Baldcypress Baldcypress Alder decay-resistant species may require preserva- (old growth)' (young Ashes tive treatment for important structural or Catalpa growth)' Aspens other uses where failure would endanger life Cedars Douglas-fir Basswood Cherry, black Honeylocust Beech or require expensive repairs. Preservative Chestnut Larch, Birches treatments and methods are discussed in chap- Cypress, Arizona western Buckeye ter 18. Junipers Oak, swamp Butternut Locust, black ^ chestnut Cottonwood Mesquite Pine, eastern Elms Mulberry, red ' white ^ Hackberry CHEMICAL RESISTANCE Oak: Southern pine: Hemlocks Bur Longleaf ' Hickories Chestnut Slash ' Magnolia Wood is highly resistant to many chemicals. Gambel Tamarack Maples In the chemical processing industry, it is the Oregon white Oak (red and preferred material for numerous applications, Post black White species) such as various types of tanks and other con- Osage orange ^ Pines (other tainers, and for structures adjacent to or hous- Redwood than long- Sassafras leaf, slash, ing chemical equipment. Wood is widely used Walnut, black and eastern in cooling towers where the hot water to be Yew, Pacific ' white) Poplars cooled contains boiler conditioning chemicals Spruces as well as dissolved chlorine for algae suppres- Sweetgum sion. It is also used in the fabrication of build- True firs (western ings for bulk chemical storage where the wood and eastern) may be in direct contact with chemicals. Willows Yellow-poplar Wood owes its extensive use in chemical ' The southern and eastern pines and baldcypress are processing operations largely to its superiority now largely second growth with a large proportion of over cast iron and ordinary in resistance sapwood. Consequently, substantial quantities of heart- to mild acids and solutions of acidic salts. wood lumber of these species are not available. ^ These woods have exceptionally high decay resist- While iron is superior to untreated wood in resistance to alkaline solutions, wood may be 3-17 Table 3-11.—Grouping of some woods imported The second type of action causes perma- into the United States according to approxi- nent changes due to hydrolysis of cellulose and mate relative heartwood decay resistance hemicelluloses by acids or acidic salts, oxida- tion of wood substance by oxidizing agents, or Resistant or Moderately Slightly or delignification and solution of hemicelluloses very resistant resistant nonresistant by alkalies or alkaline salt solutions. Experi- Angélique Andiroba ^ Balsa ence and available data indicate species and , Apamate Apitong * Banak Brazilian Avodire Cativo conditions where wood is equal or superior to rosewood Capirona Ceiba other materials in resisting degradative ac- Caribbean pine European Jelutong tions of chemicals. In general, heartwood of Courbaril walnut Limba Pncino Gola Lupuna such species as cypress, Douglas-fir, southern Qoncalo alves Khaya Mahogany, pine, redwood, maple, and white oak is quite Greenheart Laurel Philippine : resistant to attack by dilute mineral and or- Guijo Mahogany, Mayapis Philippine : White lauan ganic acids. Oxidizing acids, such as nitric Jarrah Almon Obeche acid, have a greater degradative action than Kapur Bagtikan Parana pine nonoxidizing acids. Alkaline solutions are more Karri Red lauan Ramin Kokrodua Tanguile Sande destructive than acidic solutions, and hard- (Afrormosia) Ocote pine Virola woods are more susceptible to attack by both Lapacho Palosapis acids and alkalies than softwoods. Lignum vitae Sapele Mahogany, Highly acidic salts tend to hydrolyze wood American when present in high concentrations. Even Meranti * Peroba de campos relatively low concentrations of such salts have Primavera shown signs that the salt may migrate to Santa Maria the surface of railroad ties that are occasion- Spanish-cedar Teak ally wet and dried in a hot, arid region. This migration, combined with the high concentra- ^ More than 1 species included, some of which may tions of salt relative to the small amount of vary in resistance from that indicated. water present, causes an acidic condition suf- ficient to make wood brittle. treated to greatly enhance its durability in Iron salts, which develop at points of con- this respect. tact with tie plates, bolts, and the like, have In general, heartwood is more resistant to a degradative action on wood, especially in the chemical attack than sapwood, basically be- presence of moisture. In addition, iron salts cause heartwood is more resistant to penetra- probably precipitate toxic extractives and thus tion by liquids. The heartwoods of cypress, lower the natural decay resistance of wood. southern pine, Douglas-fir, and redwood are The softening and discoloration of wood around preferred for water tanks. Heartwoods of the corroded iron fastenings is a commonly ob- first three of these species are preferred where served phenomenon; it is especially pronounced resistance* to chemical attack is an important in acidic woods, such as oak, and in woods factor. These four species combine moderate such as redwood which contain considerable to high resistance to water penetration with tannin and related compounds. The oxide layer moderate to high resistance to chemical attack formed on iron is transformed through reac- and decay. tion with wood acids into soluble iron salts Chemical solutions may affect wood by two which not only degrade the surrounding wood general types of action. The first is an almost completely reversible effect involving swelling but probably catalyze the further corrosion of of the wood structure. The second type of ac- the metal. The action is accelerated by mois- tion is irreversible and involves permanent ture; oxygen may also play an important role changes in the wood structure due to alteration in the process. This effect is not encountered of one or more of its chemical constituents. with well-dried wood used in dry locations. In the first type, liquids such as water, Under damp use conditions, it can be avoided alcohols, and some other organic liquids swell or minimized by using corrosion-resistant fas- the wood with no degradation of the wood tenings. structure. Removal of the swelling liquid al- Many substances have been employed as im- lows the wood to return to its original condi- prégnants to enhance the natural resistance of tion. Petroleum oils and do not swell wood to chemical degradation. One of the more wood. economical treatments involves pressure im-

3-18 pregnation with a viscous coke-oven coal tar tions. It increases as the density, moisture to retard liquid penetration. Acid resistance content, or extractive content of the wood in- of wood is increased by impregnation with creases. phenolic resin solutions followed by appro- Figure 3-5 shows the average thermal con- priate drying and curing. Treatment with fur- ductivity perpendicular to the grain as related furyl alcohol has been used to increase to wood density and moisture content up to resistance to alkaline solutions. A newer de- approximately 40 percent moisture content. velopment involves massive impregnation with This chart is a plot of the empirical equation : a monomeric resin, such as methyl methacry- late, followed by polymerization. Chapters 16, Ä: = S(1.39 + 0.028M) +0.165 17, and 18 discuss coatings and finishes, other chemical treatments, and preservation. where k is thermal conductivity in Btu • in./hr • deg F, S is specific gravity based on volume THERMAL PROPERTIES at current moisture content and weight when ovendry, and M is the moisture content in Four important thermal properties of wood percent of dry weight. For wood at a moisture are (1) thermal conductivity, (2) specific content of 40 percent or greater, the following heat, (3) thermal diffusivity, and (4) coeffi- equation has been applied : cient of thermal expansion. Thermal conduc- tivity is a measure of the rate of heat flow ^ = 5(1.39 + 0.038^) +0.165 through materials subjected to a temperature gradient. Specific heat of a material is the The equations presented were derived by aver- ratio of the heat capacity of the material to aging the results of studies on a variety of the heat capacity of water; the heat capacity species. Individual wood specimen conductivity of a material is the thermal energy required will vary from these predicted values because to produce one unit change of temperature in of the five variability sources noted above. one unit mass. Thermal diffusivity is a meas- ure of how quickly a material can absorb heat Specific Heat from its surroundings; it is the ratio of ther- The specific heat of wood depends on the mal conductivity to the product of density and temperature and moisture content of the wood specific heat. The coeflîcient of thermal expan- but is practically independent of density or sion is a measure of the change of dimension species. Specific heat of dry wood is approx- caused by temperature change. imately related to temperature t, in °F. by Thermal Conductivity Specific heat = 0.25 + 0.0006* The thermal conductivity of common struc- When wood contains water, the specific heat tural woods is a small fraction of the conduc- is increased because the specific heat of water tivity of metals with which it often is mated is larger than that of dry wood. The apparent in construction. It is about two to four times specific heat of moist wood, however, is larger that of common insulating material. For than would be expected from a simple sum of example, structural softwood lumber has a the separate effects of wood and water. The conductivity of about 0.8 British thermal units additional apparent specific heat is due to per inch per hour per foot per degree thermal energy absorbed by the wood-water Fahrenheit (Btu • in/hr • deg F) compared bonds. As the temperature increases the ap- with 1390 for aluminum, 320 for steel, 8 for parent specific heat increases because the concrete, 5 for glass, 3 for , and 0.3 for energy of absorption of wood increases with mineral wool. temperature. The thermal conductivity of wood is af- If the specific heat of water is considered fected by a number of basic factors: (1) den- to be unity, the specific heat of moist wood sity, (2) moisture content, (3) extractive con- is given by : tent, (4) grain direction, and (5) structural irregularities such as checks and knots. It is Specific heat = M + CQ nearly the same in the radial and tangential 1+M direction with respect to the growth rings but is 2.0 to 2.8 times greater parallel to the grain where M is the fractional moisture content of than in either the radial or tangential direc- the wood, Co is the specific heat of dry wood.

3-19 2.0 SPECIFI C GRAVnry 0.28 > 1.8 0.26

0.24 1.6 0.6^ ^0.6^ 0.22 ^ 1.4 ^■"^'^ ^^^--^ 0.56 0.20

«M ^^0.52 ^ ^ ^ 0.18 1.2 0.16 ^ ^ ^ ^^0.^0 1.0 I O.I4 c^ ^^0.36 ^ -;;-;::;:;: .^0.32 0.12 0.8 .,^0.26 ^^ ^^ rrrr . 0.24 0.10 0.6 . 0.20 I 0.08 0.16 = 0.12 0.06 0.4 ^^ 1 — — 0.08 0.04 0.2 0.02 1 8 12 16 20 24 28 MOISTURE CONTENT (PERCENT)

M 140 415 Figure 3-5.—Computed thermal conductivity of wood perpendicular to grain as related to moisture content and specific gravity.

3-20 and A is the additional specific heat due to parallel-to-the-grain coefficients and thus are of the wood-water bond energy. A increases with more practical interest. The radial and tan- increasing temperature. For wood at 10 per- gential thermal expansion coefficients for oven- cent moisture content, A ranges from about dry wood, a, and «t, can be approximated by 0.02 at 85° F. to about 0.04 at 140° F. A the following equations, over an ovendry spe- ranges from about 0.04 at 85° F. to about cific gravity range of about 0.1 to 0.8: 0.09 at 140° F. for wood at about 30 percent moisture content. a.= [(32)(specific gravity) + 9.9] [10"^] per °F. Thermal Diffusivlty «i=[(33)(specific gravity) +18.4] [10-^] per °F. Because of the small thermal conductivity Thermal expansion coeflScients can be consid- and moderate density and specific heat of wood, ered independent of temperature over the the thermal diffusivity of wood is much smaller temperature range of - 60° to +130° F. than that of other structural materials such Wood that contains moisture reacts to vary- as metals, brick, and stone. A typical value ing temperature differently than does dry for wood is 0.00025 inch^ per second compared wood. When moist wood is heated, it tends to to 0.02 inch^ per second for steel, and 0.001 expand because of normal thermal expansion inch^ per second for mineral wool. For this and to shrink because of loss in moisture con- reason wood does not feel extremely hot or tent. Unless the wood is very dry initially cold to the touch as do some other materials. (perhaps 3 or 4 pet. M.C. or less), the shrink- Few investigators have measured the dif- age due to moisture loss on heating will be fusivity of wood directly. Since diffusivity is greater than the thermal expansion, so the net defined as the ratio of conductivity to the prod- dimensional change on heating will be negative. uct of specific heat and density, conclusions Wood at intermediate moisture levels (about regarding its variation with temperature and 8 to 20 pet.) will expand when first heated, density often are based on calculating the ef- then gradually shrink to a volume smaller than fect of these variables on specific heat and the initial volume, as the wood gradually loses conductivity. water while in the heated condition. All investigations illustrate that diffusivity Even in the longitudinal (grain) direction, is influenced slightly by both specific gravity where dimensional change due to moisture and moisture content in an inverse fashion. change is very small, such changes will still The diffusivity increases approximately 0.0001 predominate over corresponding dimensional inch^ per second over a decreasing specific changes due to thermal expansion unless the gravity range of 0.65 to 0.30. Calculations sug- wood is very dry initially. For wood at usual gest the effect of moisture is to increase dif- moisture levels, net dimensional changes will fusivity by about 0.00004 inch^ per second as generally be negative after prolonged heating. the moisture content is reduced from 12 to 0 percent. ELECTRICAL PROPERTIES Coefficient of Thermal Exparision The most important electrical properties of wood are (1) conductivity, (2) dielectric con- The thermal expansion coefficients of com- stant, and (3) dielectric power factor. pletely dry wood are positive in all directions— The conductivity of a material determines that is, wood expands on heating and contracts the current that will flow when the material on cooling. Only limited research has been car- is placed under a given voltage gradient. The ried out to explore the influence of wood prop- dielectric constant of a nonconducting material erty variability on thermal expansion. The determines the amount of electric potential en- linear expansion coefficient of ovendry wood ergy, in the form of induced polarization, that parallel to the grain appears to be independent is stored in a given volume of the material of specific gravity and species. In tests of both when that material is placed in an electric hardwoods and softwoods, the parallel-to-the- field. The power factor of a nonconducting ma- grain values have ranged from about 0.0000017 terial determines the fraction of stored energy to 0.0000025 per degree Fahrenheit. that is dissipated as heat when the material The linear expansion coefficients across the experiences a complete polarize-depolarize cy- grain (radial and tangential) are proportional cle. to wood density. These coeflicients range from Examples of industrial wood processes and about five to over ten times greater than the applications in which electrical properties of 3-21 wood are important include crossarms and The resistance values were obtained using a poles for high-voltage powerlines, linemen's standard moisture meter electrode at 80° F. tools, and the heat-curing of adhesives in wood Conductivity is greater along the grain than products by high-frequency electric fields. across the grain and slightly greater in the Moisture meters for wood utilize the relation radial direction than in the tangential direc- between electrical properties and moisture con- tion. Relative conductivities in the longitudi- tent to estimate the moisture content. nal, radial, and tangential directions are in the approximate ratio of 1.0:0.55:0.50. Elecfrkal Conducfivity When wood contains abnormal quantities of water-soluble salts or other electrolytic sub- The electrical conductivity of wood varies stances, such as from preservative or fire- slightly with applied voltage and approxi- retardant treatment or prolonged contact with mately doubles for each temperature increase seawater, the electrical conductivity may be of 10° C. The electrical conductivity of wood substantially increased. The increase is small or its reciprocal, resistivity, varies greatly with when the moisture content of the wood is less moisture content, especially below the fiber sat- than about 8 percent but becomes large rap- uration point. As the moisture content of wood idly as the moisture content exceeds 10 or increases from near zero to fiber saturation, 12 percent. the electrical conductivity increases (resistiv- ity decreases) by 10^^ to 10^^ times. The re- sistivity is about 10^* to 10^^ ohm-meters for Dielectric Constant ovendry wood and 10^ to 10* ohm-meters for wood at fiber saturation. As the moisture con- The dielectric constant is the ratio of the tent increases from fiber saturation to complete dielectric permittivity of the material to that saturation of the wood structure, the further of free space ; it is essentially a measure of the increase in conductivity is smaller and erratic, potential energy per unit volume stored in the generally amounting to less than a hundred- material in the form of electric polarization fold. when the material is in a given electric field. Figure 3-6 illustrates the change in resist- As measured by practical tests, the dielectric ance along the grain with moisture content, constant of a material is the ratio of the capaci- based on tests of many domestic species. Vari- tance of a capacitor using the material as the ability between test specimens is illustrated dielectric, to the capacitance of the same ca- by the shaded area. Ninety percent of the ex- pacitor using free space as the dielectric. perimental data points fall within this area. The dielectric constant of ovendry wood ranges from about 2 to 5 at room temperature, and decreases slowly but steadily with increas- ing frequency of the applied electric field. It increases as either temperature or moisture content increase, with a moderate positive in- teraction between temperature and moisture. There is an intense negative interaction be- tween moisture and frequency: At 20 Hz the dielectric constant may range from 4 for dry wood to near 1,000,000 for wet wood; at 1 KHz, from 4 when dry to 5,000 wet; and at 1 MHz from 3 when dry to wet. The dielectric constant is larger for polarization parallel to the grain than for across the grain.

Dielectric Power Factor When a nonconductor is placed in an elec- MOISTURE CONTENT (PERCENT) tric field, it absorbs and stores potential en- ergy. The amount of energy stored per unit M 140 4 J4 volume depends upon the dielectric constant Figure 3-6.—Change in electrical resistance of wood with varying moisture content levels for many United States species. Ninety and the magnitude of the applied field. An percent of test values are represented by the shaded area. ideal dielectric releases all of this energy to

3-22 the external electric circuit when the field is where / is the reduced intensity of the beam removed, but practical dielectrics dissipate at a depth of œ in the material, h is the in- some of the energy as heat. The power factor cident intensity of a beam of radiation, and is a measure of that portion of the stored en- /x, the linear absorption coefficient of the ma- ergy converted to heat. Power factor values terial, is the fraction of energy removed from always fall between zero and unity. When the the beam per unit depth traversed. Where the power factor does not exceed about 0.1, the frac- density is a factor of interest in energy ab- tion of the stored energy that is lost in one sorption, the linear absorption coefficient is charge-discharge cycle is approximately equal divided by the density of the material to de- to 27r times the power factor of the dielectric; rive the mass absorption coefficient. The ab- for larger power factors, this fraction is ap- sorption coefficient of a material varies with proximated simply by the power factor itself. type and energy of radiation. The power factor of wood is large compared The linear absorption coefficient for gamma to inert plastic insulating materials ; some ma- (y) radiation of wood is known to vary di- terials, for example some formulations of rub- rectly with moisture content and density; in- ber, have equally large power factors. The versely with the y ray energy. As an example, power factor of wood varies from about 0.01 the radiation of ovendry yellow-poplar with for dry low-density woods to as large as 0.95 0.047 MEV y rays yielded linear absorption for dense woods at high moisture levels. It is coefficients ranging from about 0.065 to about usually, but not always, greater along the 0.11 per centimeter over the ovendry specific grain than across the grain. gravity range of about 0.33 to 0.62. An increase The power factor of wood is affected by in the linear absorption coefficient of about several factors, including frequency, moisture 0.01 per centimeter occurs with an increase in content, and temperature. These factors inter- moisture content from ovendry to fiber satura- act in complex ways to cause the power factor tion. Absorption of y rays in wood is of prac- to have maximum and minimum values at var- tical interest, in part, for measurement of the ious combinations of these factors. density of wood. The interaction of wood with beta {ß) ra- COEFFICIENT OF FRICTION diation is similar in character to that with y radiation, except that the absorption coeffi- The coefficient of friction depends on the cients are larger. The linear absorption coeffi- moisture content of the wood and surface cient of wood with a specific gravity of 0.5 for roughness. It varies little with species except a 0.5 MEV ß ray is about 3.0 per centimeter. for those species that contain abundant oily or The result of the larger coefficient is that even waxy extractives, such as lignum vitae. very thin wood products are virtually opaque Coefficients of static friction for wood on to ß rays. unpolished steel have been reported to be ap- The interaction of neutrons with wood is proximately 0.70 for dry wood and 0.40 for of interest because wood and the water it green wood. Corresponding values for lignum contains are compounds of hydrogen, and hy- vitae on unpolished steel are 0.20 and 0.34. drogen has a relatively large probability of in- Coefficients of static friction for smooth wood teraction with neutrons. High energy level on smooth wood are 0.60 for dry wood and neutrons lose energy much more quickly 0.83 for green wood. through interaction with hydrogen than with Coefficients of sliding friction differ from other elements found in wood. The lower en- those for static friction, and depend on the ergy neutrons that result from this interaction rate of relative movement between the rubbing thus are a measure of the hydrogen density of parts. Coefficients for wood on steel of 0.70 for the specimen. Measurement of the lower ener- dry wood and 0.15 for green wood have been gy level neutrons can be related to the moisture obtained at a relative movement of 4 meters content of the wood. per second. When neutrons interact with wood, an ad- ditional result is the production of radioactive NUCLEAR RADIATION isotopes of the elements present in the wood. The radioisotopes produced can be identified Radiation passing through matter is reduced by the type, energy, and half-life of their emis- in intensity according to the relationship sions, and the specific activity of each indicates amount of isotope present. This procedure, called neutron activation, provides a sensitive. 3-23 nondestructive method of analysis for trace BIBLIOGRAPHY elements. American Society for Testing and Materials In the discussions above, moderate radiation Standard methods for testing small clear specimens levels that leave the wood physically un- of timber. D 143 (see current edition.) Phila- changed have been assumed. Very large doses delphia, Pa. James, W. of y rays or neutrons can cause substantial deg- 1968. Effect of temperature on the readings of radation of wood. The effect of large radiation electric moisture meters. Forest Prod. J. doses on the mechanical properties of wood is 18(10): 23-31. , and Hamill, D. discussed in chapter 4. 1965. Dielectric properties of Douglas-fir measured at microwave frequencies. Forest Prod. J. 15(2): 57. Kleuters, W. 1964. Determining local density of wood by beta ray method. Forest Prod. J. 14(9): 414. Kukachka, B. F. 1970. Properties of imported tropical woods. USDA Forest Serv. Res. Pap. FPL 125. Forest Prod. Lab., Madison, Wis. Loos, Wesley 1961. Gamma ray absorption and moisture content and density. Forest Prod. J. 11(3): 145. Lynn, R. 1967. Review of dielectric properties of wood and cellulose. Forest Prod. J. 17(7): 61. McKenzie, W. M., and Karpovich, H. 1968. Frictional behavior of wood. Wood Sei. and Tech. 2(2): 138. MacLean, J. D. 1941. Thermal conductivity of wood. Trans. Amer. Soc. Heat. Ventil. Eng. 47: 323. Nanassy, A. 1964. Electric polarization measurements on yel- low birch. Can. J. Phys. 42(6): 1270. Panshin, A. J., and deZeeuw, C. 1970. Textbook of wood technology. Vol. 1. 3rd Edition. McGraw-Hill. Wangaard, Frederick F. 1969. Heat transmissivity of southern pine wood, plywood, fiberboard, and particleboard. Wood Sei. 2(1): 54. Wong, Phillip T.Y. 1964. Thermal conductivity and diifusivity of partially charred wood. Forest Prod. J. 14(5): 195.

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3-25

FS-354 Chapter 4 MECHANICAL PROPERTIES OF WOOD

Orthotropic Nature of Wood 4-2 Elastic Properties of Clear Wood 4-2 Modulus of Elasticity 4-2 Modulus of Rigidity 4-3 Poisson's Ratio 4-3 Strength Properties of Clear Straight-Grained Wood 4-3 Common Properties 4-3 Less Common Properties 4-3 Vibration Properties 4-4 Speed of Sound 4-4 Internal Friction 4-4 Summary Tables on Mechanical Properties of Clear Straight-Grained Wood 4-4 Influence of Growth Characteristics on the Proper- ties of Clear Straight-Grained Wood 4-25 Speciñc Gravity 4-25 Knots 4-26 Fiber and Ring Orientation 4-27 Reaction Wood 4-29 Compression Failures 4-30 Pitch Pockets 4-31 Bird Peck 4-31 Extractives 4-32 Timber From Live Versus Dead Trees 4-32 Effect of and Service Environment on Mechanical Properties of Clear Straight- Grained Wood _ 4-32 Moisture Content—Drying 4-32 Temperature 4-34 Time __ 4-36 Chemicals 4-38 Nuclear Radiation 4-39 Molding and Staining Fungi 4-39 Decay 4-39 Insect Damage 4-40 Bibliography 4-40 Appendix 4-40

4-1 MECHANICAL PROPERTIES OF WOOD

Mechanical properties discussed in this chap- ter have been obtained from tests of small RADIAL pieces of wood termed **clear" and "straight grained" because they did not contain char- acteristics such as knots, cross grain, checks, and splits. These test pieces do contain wood structure characteristics such as growth rings that occur in consistent patterns within the piece. Clear wood specimens are usually con- sidered "homogeneous'' in wood mechanics. TANGENTIAL Many of the mechanical properties of wood LONGITUDINAL tabulated in this chapter were derived from M 140 728 extensive sampling and analysis procedures. Figure 4-1.—The three principal of wood with respect to These properties often are represented as the grain direction and growth rings. average mechanical properties of the species and are used to derive allowable properties for design. A number of other properties, particu- ELASTIC PROPERTIES OF CLEAR WOOD larly those less common and those for imported species, often are based on a more limited num- Twelve constants (nine are independent) ber of specimens not subject to the same are needed to describe the elastic behavior of sampling and analysis procedures. The appro- wood: Three moduli of elasticity, E, three priateness of these latter properties to repre- moduli of rigidity, G, and six Poisson's ratios, sent the average properties of a species often ¡I. The moduli of elasticity and Poisson's ratios is uncertain; nevertheless, they illustrate im- are related by expressions of the form portant wood behavior and provide guidance for wood design. Variability, or variation in properties, is common to all materials. Since wood is a nat- General relations between stress and strain ural material and the tree is subject to num- for a homogeneous, orthotropic material can erous constantly changing influences (such as be found in texts on anisotropic elasticity. moisture, soil conditions, and growing space), wood properties vary considerably even in Modulus of Elasticity clear material. This chapter provides informa- tion where possible on the nature and magni- The three moduli of elasticity demoted by tude of property variability. EL, Eli, and ET are, respectively, the elastic moduli along longitudinal, radial, and tangen- tial axes of wood. These moduli are usually obtained from compression tests; however, ORTHOTROPIC NATURE OF WOOD data for ER and ET are not extensive. Y^li^^s of Wood may be described as an orthotropic ER and ET for samples from a few species are material; that is, it has unique and independ- presented in table 4-1 as ratios with £7^. These ent mechanical properties in the directions of ratios, as well as the three elastic constants themselves, vary within and between species three mutually perpendicular axes—longitudi- and with moisture content and specific gravity. nal, radial, and tangential. The longitudinal Often EL determined from bending, rather axis (L) is parallel to the fiber (grain) ; the than from an axial test, is the only E available. radial axis (R) is normal to the growth rings Averag*e values of EL obtained from bending (perpendicular to the grain in the radial direc- tests are given in tables 4-2, 4-3, and 4-4. tion) ; and the tangential axis (T) is per- A representative coefficient of variation of EL pendicular to the grain but tangent to the determined with bending tests for clear wood is growth rings. These axes are shown in figure reported in table 4-5. E^ as tabulated includes 4-1. an effect of shear deflection. EL from bending

4-2 can be increased by 10 percent to approxi- member and is proportional to the maximum mately remove this effect. This adjusted bend- moment borne by the specimen. The work to ing EL can be used to obtain ER and ET from maximum load is a measure of the energy table 4-1. absorbed by the specimen as it is slowly loaded to failure. On the other hand, the impact bend- Modulus of Rigidity ing height of drop is related to the energy absorption due to a rapid or falling load. Hard- The three moduli of rigidity denoted by ness is the load required to embed a 0.444-inch GLR, GLT, GRT are the elastic constants in the ball to one-half its diameter in a direction LR, LT, and RT planes, respectively. For ex- perpendicular to the grain. ample, GLR is the modulus of rigidity based on shear strain in the LR and shear stresses Less Common Properties in the LT and RT planes. Values of shear moduli for samples of a fev^ species expressed Strength properties less commonly meas- as ratios with EL are given in table 4-1. As ured in clear wood include tensile strength par- with moduli of elasticity, the moduli of rigidity allel to the grain, torsion, toughness, creep, vary within and between species and with rolling shear, and fatigue resistance. moisture content and specific gravity. Tensile Strength Parallel to Grain Poisson's Ratio Relatively few data are available on the The six Poisson's ratios are denoted by ¡JLLR, tensile strength of various species parallel to i^RLf i^LTy ßTL, i^RTy ¡Ji R- The first Ictter of the grain. In the absence of sufficient tension test subscript refers to direction of applied stress data, the modulus of rupture values are some- and the second letter refers to direction of times substituted for tensile strength of small, lateral deformation. For example, ¡JLLR is the clear, straight-grained pieces of wood. The Poisson's ratio for deformation along the radial modulus of rupture is considered to be a low axis caused by stress along the longitudinal or conservative estimate of tensile strength for axis. Values of Poisson's ratios for samples of these specimens. Chapter 6 should be consulted a few species are given in table 4-1. Poisson's for discussion of the tensile properties of com- ratios vary within and between species and are mercial structural members. Table 4-6 lists affected slightly by moisture content. average tensile strength values for a limited number of specimens of a few species. STRENGTH PROPERTIES OF CLEAR STRAIGHT-GRAINED WOOD Torsion For solid wood members, the torsional shear Common Properties strength often is taken as the shear strength Strength values most commonly measured parallel to the grain. Two-thirds of this value and represented as "strength properties'* for often is used as the torsional shear stress at design include the modulus of rupture in bend- the proportional limit. ing, the maximum stress in compression paral- lel to the grain, compression strength per- Toughness pendicular to the grain, and shear strength parallel to the grain. Additional measurements Toughness represents the energy required to often made include work to maximum load in rapidly cause complete failure in a centrally bending, impact bending strength, tensile loaded bending specimen. Table 4-7 gives aver- strength perpendicular to the grain, and hard- age toughness values for samples of a few ness. These properties, grouped according to hardwood and softwood species. Table 4-5 re- the broad forest tree categories of hardwood cords the average coefficient of variation for and softwood (not correlated with hardness toughness as determined from approximately or softness), are given in tables 4-2, 4-3, and 50 species. 4-4 for many of the commercially important Fatigue Strength species. Coefficients of variation for these prop- erties from a limited sampling of specimens The resistance of wood to fatigue is some- are reported in table 4-5. times an important consideration in design. The modulus of rupture in bending reflects Tests indicate that wood, like many fibrous the maximum load-carrying capacity of the materials, is less sensitive to repeated loads

4-3 than are more crystalline structural materials, Internal Friction such as metals. In proportion to ultimate strength values, the fatigue strength of wood When solid material is strained, some me- is^ higher than for some of the metals. A brief chanical energy is dissipated as heat. Internal résumé of the results of several fatigue studies friction is the term used to denote the mech- is given in table 4-8. Interpretation of fatigue anism that causes this energy dissipation. data, and a discussion of fatigue as a function The internal friction mechanism in wood is a of the service environment, are included later complex function of temperature and moisture in this chapter. content. At normal ambient temperatures the internal friction generally increases as the Rolling Shear Strength moisture content increases, up to the fiber satu- ration point. At room temperature internal The term "rolling shear" describes the shear friction is a minimum at about 6 to 8 percent strength of wood where the shearing force is moisture content. Below room temperature the in a longitudinal-transverse plane and per- minimum occurs at a higher moisture content ; pendicular to the grain. Test procedures for above room temperature it occurs at a lower rolling shear in solid wood are of recent origin ; moisture content. The parallel-to-grain inter- few test values have been reported. In limited nal friction of wood under normal use condi- tests, rolling shear strengths were 10 to 20 tions of moisture content and temperature is percent of the parallel-to-grain shear values. approximately 10 times that of structural Rolling shear values were about the same in metals, explaining in part why wood structures the longitudinal-radial and the longitudinal- damp vibration more quickly than metal struc- tangential planes. tures of similar design. VIBRATION PROPERTIES SUMMARY TABLES ON MECHANICAL The vibration properties of primary interest PROPERTIES OF CLEAR STRAIGHT- in structural materials are the speed of sound GRAINED WOOD and the damping capacity or internal friction. The mechanical properties listed in tables Speed of Sound 4-1 through 4-7 are based on a variety of sampling methods. Generally, the greatest The speed of sound in a structural material amount of sampling is represented in tables varies directly with the square of the 4-2, 4-3, and 4-4. The values in table 4-2 modulus of elasticity and inversely with the are averages derived for a number of species square root of the density. For example, a grown in the united States. The table value parallel-to-grain value for speed of sound of is intended to estimate the average clear wood 150,000 inches per second corresponds to a property of the species. Many of the values modulus of elasticity of about 1,800,000 p.s.i., were obtained from test specimens taken at and a density of 30 pounds per cubic foot. heights between 8 and 16 feet above the stump The speed of sound in wood varies strongly of the tree. Values reported in table 4-3 repre- with grain angle since the transverse modulus sent average clear wood properties of species of elasticity may be as small as 1/20 of the grown in Canada and commonly imported into longitudinal value. Thus, the speed of sound the United States. across the grain is about one-fifth to one-third Methods of data collection and analysis have of the longitudinal value. changed over the years that the data in tables The speed of sound decreases with increas- 4-2 and 4-3 have been collected. In addition, ing temperature or moisture content in pro- the character of some forests changes with portion to the influence of these variables on time. Thus, when these data are used as a the modulus of elasticity and density. The speed basis for critical applications such as stress of sound decreases slightly with increasing grades of lumber, the current appropriateness frequency and amplitude of vibration, although of the data should be reviewed. for most common applications this effect is too Values reported in table 4-4 were collected small to be significant. There is no recognized from the world literature; thus, the appro- independent effect of species on the speed of priateness of these properties to represent a sound. Variability in the speed of sound in species is not known. The properties reported wood is directly related to the variability of in tables 4-1, 4-6, 4-7, and 4-8 are not in- modulus of elasticity and density. tended to represent species characteristics in

4-4 the broad sense; they suggest the relative in- 6, "Lumber Stress Grades and Allowable fluence of species and other specimen param- Properties." eters on the mechanical behavior recorded. Specific gravity is reported in many of the Variability in properties can be important tables because it often is used as an index of in both production and consumption of wood clear wood properties. The specific gravity products. Often the fact that a piece may be values given in tables 4-2 and 4-3 represent stronger, harder, or stiffer than the average is the estimated average clear wood specific of less concern to the user than if it is weaker ; gravity of the species. In the other tables, the however, this may not be true if lightweight specific gravity represents only the specimens material is selected for a speciñc purpose or if tested. The variability of specific gravity, re- harder or tougher material is hard to work. presented by the coefficient of variation de- It is desirable, therefore, that some indication rived from tests on 50 species, is included in of the spread of property values be given. table 4-5. Average coefficients of variation for many me- Mechanical and physical properties as meas- chanical properties are presented in table 4-5. ured and reported often reflect not only the The mechanical properties reported in the characteristics of the wood but also the in- tables are significantly affected by the moisture fluence of the shape and size of test specimen content of the specimens at the time of test. and of test. The methods of test used Some tables include properties evaluated at dif- to establish properties in tables 4-2, 4-3, 4-6, fering moisture levels ; these moisture levels and 4-7 are based on standard procedures, are reported. As indicated in the tables, many ASTM Designation D 143. The methods of of the dry test data have been adjusted to a test for properties presented in other tables common moisture content base of 12 percent. are reported in the bibliography at the end The differences in properties displayed in the of this chapter. tables as a result of differing moisture levels Names of species listed in the tables con- are not necessarily consistent for larger wood form to standard nomenclature of the U.S. pieces such as lumber. Guidelines for adjusting Forest Service. Other common names may be clear wood properties to arrive at allowable used locally, and frequently one common name properties for lumber are discussed in chapter is applied to several species.

Tables 4-2, 4-3, and 4-4 are repeated in metric (SI) units in appendix 4-1 at the end of this chapter.

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4S I p g^Q-W-« I P S-rt ¿o 3 '"■tí'«3'«5 ^ T5 2 o o §•- gS O ?! 1^ S o tí C3 O) o 03 o 4-14 Table 4-3.—Mechanical properties of some commercially important woods grown in Canada and imported into the United States ^'^

Static bending Compres- Compres- Shear Common names Specific sion sion parallel of species . gravity Modulus of Modulus of parallel perpen- to grain rupture elasticity to grain dicular —maxi- —maxi- to grain mum mum —fiber shearing crushing stress strength strength at pro- tional limit P,s.L Million P,s.l P.s.i. P.s.i. P.s.i.

HARDWOODS Aspen : Quaking i 0.37 5,500 1.31 2,350 200 720 9,800 1.63 5,260 510 980 790 Big-toothed i .39 5,300 1.08 2,390 210 9,500 1.26 4,760 470 1,100 Cottonwood : Balsam, poplar ___i .37 5,000 1.15 2,110 180 670 10,100 1.67 5,020 420 890 560 Black / .30 4,100 .97 1,860 100 7,100 1.28 4,020 260 860

Eastern .35 4,700 .87 1,970 210 770 ■■{ 7,500 1.13 3,840 470 1,160 SOFTWOODS

Cedar: 880 Alaska- / .42 6,600 1.34 3,240 350 11,600 1.59 6,640 690 1,340 660 Northern white- _ f .30 3,900 .52 1,890 200 6,100 .63 3,590 390 1,000 700 Western redcedar _/ .31 5,300 1.05 2,780 280 7,800 1.19 4,290 500 810 920 Douglas-fir / .45 7,500 1.61 3,610 460 12,800 1.97 7,260 870 1,380

Fir: 680 Subalpine . ^ -_/ .33 5,200 1.26 2,500 260 8,200 1.48 5,280 540 980 710 Pacific silver ---/ .36 5,500 1.35 2,770 230 10,000 1.64 5,930 520 1,190 680 Balsam _ - / .34 5,300 1.13 2,440 240 8,500 1.40 4,980 460 910

Hemlock : Eastern ._ Í .40 6,800 1.27 3,430 400 910 9,700 1.41 5,970 630 1,260

Western / .41 7,000 1.48 3,580 370 750 11,800 1.79 6,770 660 940

Larch, western / .55 8,700 1.65 4,420 520 920 15,500 2.08 8,840 1,060 1,340

4-15 Table 4-3.—Mechanical properties of some commercially important woods grown in Canada and imported into the United States ^^^—Continued

Static bending Compres- Compres- Shear Common names Specific sion sion parallel of species gravity- Modulus of Modulus of parallel perpen- to grain rupture elasticity to grain dicular —maxi- —^maxi- to grain mum mum —fiber shearing crushing stress strength strength at pro- portional limit P.sd, Million P.sA. P.s.i. P.s.l P.S.Í,

SOFTWOODS—continued Pine: Eastern white / .36 5,100 1.18 2,590 240 640 9,500 1.36 5,230 490 880 Jack f .42 6,300 1.17 2,950 340 820 11,300 1.48 5,870 830 1,190 Lodgepole Í .40 5,600 1.27 2,860 280 720 11,000 1.58 6,260 530 1,240 Ponderosa Í .44 5,700 1.13 2,840 350 720 10,600 1.38 6,130 760 1,020 Red I .89 5,000 1.07 2,370 280 710 10,100 1.38 5,500 720 1,090 Western white Í .36 4,800 1.19 2,520 240 650 9,300 1.46 5,240 470 920 Spruce : Black Í .41 5,900 1.32 2,760 300 800 11,400 1.52 6,040 620 1,250 Engelmann Í .38 5,700 1.25 2,810 270 700 10,100 1.55 6,150 540 1,100 Red f .38 5,900 1.32 2,810 270 810 10,300 1.60 5,590 550 1,330 Sitka r .35 5,400 1.37 2,560 290 630 10,100 1.63 5,480 590 980 White ^__r .35 5,100 1.15 2,470 240 670 9,100 1.45 5,360 500 980 Tamarack _ .48 6,800 1.24 3,130 410 920 11,000 1.36 6,510 900 1,300

' Results of tests on small, clear, straight-grained ^ The values in the first line for each species are from specimens. Property values based on American Society tests of green material; those in the second line are for Testing and Materials Standard D 2555-70, "Stand- adjusted from the green condition to 12 pet. moisture ard methods for establishing clear wood values." Infor- content using dry to green clear wood property ratios mation on additional properties can be obtained from as reported in ASTM D 2555-70. Specific gravity is Department of , Canada, Publication No. 1104. based on weight when ovendry and volume when green.

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Coefficient of Property variation ' Pet Static bending: Fiber stress at proportional limit _ . 22 Modulus of rupture 16 Modulus of elasticity 22 Work to maximum load 34 Impact bending, height of drop causing complete failure 25 Compression parallel to grain : Fiber stress at proportional limit 24 Maximum crushing strength 18 Compression perpendicular to grain, fiber stress at proportional limit 28 Shear parallel to grain, maximum shear- ing strength 14 Tension perpendicular to grain, maxi- mum tensile strength 25 Hardness : Table 4-6.—Average parallel-to-grain tensile Perpendicular to grain 20 strength for specimens of some species of Toughness 34 wood^ Specific gravity 10 ^ Values given are based on results of tests of green Specific Tensile wood from approximately 50 species. Values for wood Species gravity strength adjusted to 12 pet. moisture content may be assumed to be approximately of the same magnitude. P.8d. HARDWOODS Elm: i^eaarCedar

SOFTWOODS Douglas-fir, interior northT,^,.fV, ^J -46 jg|9(^Q15,600 Fir: California red { 'JJ {¡f^^ Pacific silver 1 -J^ 13^00 Larch, western { f^ J^jOO Pine: Eastern white { H {[f^^

Virginiavívcrír^io _.^J -45^g 13,700^^^QQ Red - - .42 15,300 Í 32 12 300 Spruce, Engelmann ^ '^^ 13*000 ^ Results of tests on small, clear, straight-grained specimens. The values in the first line for each species are from tests of green material; those in the second line are from tests of dry material with the properties adjusted to 12 pet. moisture content. Specific gravity values are not from the tension specimens but others representing the species shipment. Specific gravity is based on weight when ovendry and volume when green and an adjustment to approximately 12 pet. moisture content.

4-22 Table 4-7.—Average toughness values ^ for sanvples of a few species of wood

Toughness ^ Species Moisture Specific content gravity ^ Radial Tangential Pet. InAb. InAb, HARDWOODS Birch, yellow 12 0.65 500 620 Hickory : (Mockernut, pignut, sand) _/ Green .64 700 720 I 12 .71 620 660

Maple, sugar 14 .64 370 360

Oak, red : Pin 12 .64 430 430 Scarlet 11 .66 510 440 Oak, white : Overcup / Green .56 730 680 I 13 .62 340 310

Sweetgum / Careen .48 340 330 \ 13 .51 260 260 Willow, black Í Green 310 360 I 11 .40 210 230 Yellow-poplar Í Green .43 320 300 I 12 .45 220 210 SOFTWOODS

Cedar : Alaska- 10 .48 210 230 Western redcedar 9 .33 90 130

Douglas-fir : Coast Í Green .44 210 360 I 12 .47 200 360 Interior West . _ / Green .48 200 300 I 13 .51 210 340 Interior North f Green .43 170 240 I 14 .46 160 250 Interior South / Green .38 130 180 I 14 .40 120 180

Fir: California red _ Í Green .36 130 180 I 12 .39 120 170 Noble --- / Green .36 240 I 12 .39 220 Pacific silver / Green .37 150 230 j 13 .40 170 260 White / Green .36 140 220 I 13 .38 130 200

Hemlock : Mountain / Green .41 250 280 \ 14 .44 140 170 Western -. _ / Green .38 150 170 \ 12 .41 140 210

Larch, western / Green .51 270 400 \ 12 .55 210 340

4-23 Table 4-7.—Average toughness values ^ for sanvples of a few species of wood—continued

Toughness ' Species Moisture Specific content gravity ^ Radial Tangential Pet InAb, In,-lb. SOFTWOODS—Continued Pine: Eastern white _ _ _ / ^^^^^ .33 120 160 I 12 .34 110 120 Jack / G^^e^ .41 200 380 I 12 .42 140 240 Loblolly I Green .48 310 380 .51 160 260 Lodgepole Green .38 160 210 Ponderosa Green .38 190 270 11 .43 150 190 Red _ r Gï^een .40 210 350 I 12 .43 160 290 Shortleaf / Green .47 290 400 .50 150 230 Slash Jt Green1^ .55 350 450 I 12 .59 210 320 Virginia / Green .45 340 470 I 12 .49 170 250 Redwood : Old-growth r Green .39 110 200 I 11 .39 90 140 Young-growth / Green .33 110 140 I 12 .34 90 110 Spruce, Engelmann / Green .34 150 190 I 12 .35 110 180

* Results of tests on small, clear, straight-grained ' Properties based on specimen size of 2 cm. square by specimens. 28 cm. long; radial indicates load applied to radial face ^ Based on ovendry weight and volume at moisture and tangential indicates load applied to tangential face content of test. of specimens.

Table 4r-8.—A summary of reported results of fatigue studies

Range ratio Fatigue Fatigue (minimum life strength Loading Conditions stress -^ (million (percent of maximum cycles) strength from stress) static test) Tension parallel to grain _. - Clear, air dry 0.10 30 50 Cantilever bending . - Clear, air dry, solid wood -1.00 30 30 Simple beam bending - Clear, green .10 30 60 Rotational bending - Clear, air dry -1.00 30 28

* Results from Forest Products Laboratory studies of Natural and Resin-Impregnated Compressed Lami- except for rotational bending results (from Fuller, nated Woods. J. Aero. Sei. 10(3): 81-85.) F. B., and Oberg, T. T. 1943. Fatigue Characteristics

4-24 INFLUENCE OF GROWTH CHARACTERISTICS Variations in the size of these openings and ON THE PROPERTIES OF CLEAR in the thickness of the cell walls cause some STRAIGHT-GRAINED WOOD species to have more wood substance per unit Clear straight-grained wood is used for de- volume than others and therefore to have termining fundamental mechanical properties; higher specific gravity. Specific gravity thus is however, because of natural growth character- an excellent index of the amount of wood sub- istics of trees, wood products vary in specific stance a piece of dry wood contains; it is a gravity, may contain cross grain, or have knots good index of mechanical properties so long and localized slope of grain. In addition, na- as the wood is clear, straight grained, and tural defects such as pitch pockets may occur free from defects. It should be noted, however, due to biological or climatic elements acting on that specific gravity values also reflect the the living tree. These wood characteristics presence of gums, resins, and extractives, must be taken into account in assessing actual which contribute little to mechanical prop- properties or estimating actual performance erties. of wood products. The relationships between specific gravity Specific Gravity and various other properties have been ex- The substance of which wood is composed pressed for clear straight-grained wood as is actually heavier than water, its specific power functions, based on average results of gravity being about 1.5 regardless of the spe- strength tests of more than 160 species. These cies of wood. In spite of this fact, the dry relationships, given in table 4-9, are only ap- wood of most species floats in water, and it is proximate. For any single species, more con- thus evident that part of the volume of a piece sistently accurate relationships can be obtained of wood is occupied by cell cavities and pores. from specific test results.

Table 4-9.—Functions relating mechanical properties to specific gravity of clear, straight-grained wood

Specific gravity-strength relation ^ Property Green wood Air-dry wood (12 pet. moisture — content) Static bending: Fiber stress at proportional limit P g i 10 2000*=^ 1 ß 7nnpi =» Modulus of elasticity ::::::::_miiiion"^;si! ^Tsâ ''ffi Modulus of rupture ___^.s.i. 17,600G-- 25,Ä- Work to maximum load in.-lb. per cu. in. 35.6G^'^ 32.4G^^» iotal work in.-lb. per cu. in. 103G' 72.7G' Impact bending, height of drop causing complete failure in. 114G' ''*' 94 6G* '' Compression parallel to grain : Fiber stress at proportional limit p.s.i. 5,250G 8,750G Modulus of elasticity million p.s.i. 2.91G 3 38G Maximum crushing strength p.s.i. 6,730G 12,200G Compression perpendicular to grain, fiber stress at proportional limit p.s.i. 3,000G''' 4,630G^'' Hardness : End Ib^ 3,740G'''^ 4,800G='' Side lb. 3,420G^^^ 3,770G='''

'The properties and values should be read as gravity of ovendry wood, based on the volume at the equations; for example: modulus of rupture for green moisture condition indicated, wood = 17,600G''', where G represents the specific

4^25 Figure 4-2.—A, Encasad knot; B, inlergrown knot. M 22604 r

Knots and the resulting knot is called intergrown. After the branch has died, additional growth A knot is that portion of a branch which on the trunk encloses the dead limb, and an has become incorporated in the bole of the encased knot results; fibers of the trunk are tree. The influence of a knot on mechanical not continuous with fibers of encased knots. properties of a product is due to the interrup- Encased knots and knotholes tend to be ac- tion of continuity and change in direction of companied by less cross grain than are inter- wood fibers. The influence of knots depends grown knots and are, therefore, generally less on their size, location, shape, soundness, at- serious with regard to some mechanical prop- tendant local slope of grain, and the type of erties. stress to which they are subjected. Knots decrease most mechanical properties The shape (form) of a knot appearing on because (1) the clear wood is displaced by the a sawed surface depends upon the direction knot, (2) the fibers around the knot are dis- of the exposing cut. When a branch is sawed torted causing cross grain, (3) the discon- through at right angles to its length, a nearly tinuity of wood fiber leads to stress concen- round knot results; when cut diagonally, an trations, and (4) checking often occurs around oval knot; and when sawed lengthwise, a knots in drying. Conversely, knots actually spike knot. increase hardness and strength in compression Knots are further classified as intergrown perpendicular to the grain and are objection- or encased (fig. 4-2). As long as a limb re- able in regard to these properties only in that mains alive, there is continuous growth at the they cause nonuniform wear or nonuniform junction of the limb and the trunk of the tree, stress distributions at contact surfaces.

4-26 Wood members loaded uniformly in tension determined constant. The formula has been are usually more seriously affected by knots used for modulus of elasticity as well as than if loaded in other ways. In some struc- strength properties. Values of n and associated tural members, the effect of knots on strength ratios of Q/JP have been tabulated below from depends not only on knot size but also on the available literature: location of the knot. For example, in a simply supported beam, knots on the lower side are Property n Q/P Tensile strength 1.5-2 0.04-0.07 placed in tension, those on the upper side in Compressive strength ___ 2-2.5 0.03-0.4 compression, and those at or near the neutral Bending strength 1.5-2 0.04-0.1 axis in horizontal shear. A knot has a marked Modulus of elasticity 2 0.04-0.12 effect on the maximum load a beam will sus- Toughness 1.5-2 0.06-0.1 tain when on the tension side at the point of A Hankinson-type formula can be graphi- maximum stress; knots on the compression cally depicted as a function of Q/P and n. side are somewhat less serious. Figure 4-3 shows the strength in any uirection In long columns, knots are important in expressed as a fraction of the strength paral- that they affect stiffness. In short or inter- lel to the fiber direction, plotted against angle mediate columns, the reduction in strength to the fiber direction 0, T?he plot is for a range caused by knots is approximately proportional of values of Q/P and n. to the size of the knot; however, large knots The term "slope of grain" relates the fiber have a somewhat greater relative effect than direction to the edges of a piece. Slope of do small knots. grain is usually expressed by the ratio be- Knots in round timbers, such as poles and tween a 1-inch deviation of the grain from piles, have less effect on strength than knots the edge or long axis of the piece and the in sawed timbers. Although the grain is ir- distance in inches within which this deviation regular around knots in both forms of timber, occurs (tan 0). Table 4-10 gives the effect of its angle with the surface is less in naturally grain slope on some properties of wood, as round than in sawed timber. determined from tests. The values in table Fatigue strength of clear wood is reduced 4-10 for modulus of rupture fall very close to by knots. The effect of knots, as well as an the curve in figure 4-3 for Q/P = 0.1 and n= additive effect of knots and slope of grain on 1.5. Similarly, the impact bending values fall fatigue strength is discussed under the section close to the curve for Q/P=0.05 and n=1.5; on Time-Fatigue. and for compression, Q/P=0.1, n=2,5. The effects of knots in structural lumber The term *'cross grain" indicates the condi- are discussed in chapter 6. tion measured by slope of grain. Two important forms of cross grain are spiral grain and Fiber and Ring Orientation diagonal grain (fig. 4-4). Other types are wavy, dipped, interlocked, and curly grain. In some wood product applications, the di- rections of important stresses may not coin- cide with the natural axes of fiber orientation in the wood. This may occur by choice in de- Table 4-10.—Strength of wood members with' sign, by the way the wood was removed from various grain slopes compared to strength of the log, or because of grain irregularities that a straight-grained member, expressed as per- occurred during growth. centages Elastic properties in directions other than Maximum Modulus Impact Compression along the natural axes can be obtained from slope of of bending— parallel to elastic theory. Strength properties in direc- gram m rupture height of gram— tions ranging from parallel to perpendicular member drop causing maximum complete crushing to the fibers can be approximated using a failure strength Hankinson-type formula: (50-lb. ) N = PQ P sin** (9 + Q cos^ 0 Pet, Pet. Pet. Straight-grained _ 100 100 100 in which N represents the strength property 1 in 25 96 95 100 1 in 20 93 90 100 at an angle 0 from the fiber direction, Q is 1 in 15 ^ 89 81 100 the strength across the grain, P is the strength 1 in 10 81 62 99 parallel to the grain, and n is an empirically 1 in 5 55 36 93

4-27 o 10 20 30 40 50 60 ANGLE TO FIBER DIRECTION (DEGREES)

M 140 730 Figure 4-3.—EflFect of grain angle on mechanical property of clear wood according to a Hanlcinson-type formula. O/P is tlie ratio of the mechanical property across the grain (Q) to that parallel to the grain (P); n is an empirically determined constant.

Spiral grain in a tree is caused by fibers Diagonal grain describes cross grain caused growing in a winding or spiral course about by growth rings not parallel to one or both the bole of the tree instead of in a vertical surfaces of the sawn piece. Diagonal grain is course. In sawn products spiral grain can be produced by sawing parallel to the axis (pith) defined as fibers lying in the tangential plane of the tree in a log having pronounced taper, of the growth rings, not parallel to the longi- and is a common occurrence in sawing crooked tudinal axis of the product (see fig. 4-4B for or swelled logs. a simple case). Spiral grain often is not readily Cross grain can be quite localized as a re- detected by ordinary visual inspection in sawn sult of the disturbance of growth patterns by products. The best test for spiral grain is to a branch. This condition, termed "local slope of split a sample section from the piece in the grain,*' may be present even though the branch radial direction. A nondestructive method of (knot) may have been removed in a sawing determining the presence of spiral grain is operation. Often the degree of local cross to note the alinement of pores, rays, and resin grain may be difficult to determine. ducts on the flat-grain face. Drying checks on Any form of cross grain can have a serious a flat-sawn surface follow the fibers and indi- effect on mechanical properties or machining cate the fiber slope. characteristics. Spiral and diagonal grain com-

4-28 ues are an average of an equal number of specimens with O'' and 90° growth ring orien- tation. Modulus of elasticity is least for the 45° orientation, intermediate at 0° , and highest at 90 to the growth rings. Propor- tional limit in compression increases gradually as the ring angle increases from 0° (T) to 90° (R), the total increase amounting to about one-third. Similar observations have been made in tension. For some softwoods in compression the values at 0° and 90° are about the same, with the value at 45° about two-thirds of the others. Reacffon Wood Abnormal woody tissue is frequently asso- ciated with leaning boles and crooked limbs of both conifers and hardwoods. It is generally believed that it is formed as a natural response of the tree to return its limbs or bole to a more normal position, hence the term "reaction wood." In softwoods, the abnormal tissue is called "compression wood." It is common to all softwood species and is found on the lower side of the limb or inclined bole. In hardwoods, the abnormal tissue is known as "tension wood;" it is located on the upper side of the M 139 385 inclined member, although in some instances it Figure 4-4.—Schematic views of wood specimens containing is distributed irregularly around the cross sec- straight grain and cross grain to illustrate the relationship of tion. Reaction wood is more prevalent in some fiber orientation (0-0) to the axes of the piece. Specimens A through D have radial and tangential surfaces; E through H do species than in others. not. A and E contain no cross grain. B, D, F, and H have spiral Many of the anatomical, chemical, physi- grain. C. D, G, and H have diagonal grain. cal, and mechanical properties of reaction wood differ distinctly from those of normal wood. bine to produce a more complex cross grain. Perhaps most evident is the increase in the To determine net cross grain, regardless of density over that of normal wood. The specific origin, fiber slopes on contiguous surfaces of gravity of compression wood is frequently 30 a piece must be measured and combined. The to 40 percent greater than normal, while ten- combined slope of grain is determined by tak- sion wood commonly ranges between 5 and 10 ing the square root of the sum of the squares of the two slopes. For example, assume the spiral grain slope on the flat grain surface of figure 4-4D is 1 in 12 and the diagonal grain slope is 1 in 18. The combined slope is

or a slope of 1 in 10 \\18/ '*"\12/ 10 Stresses perpendicular to the fiber (grain) direction may be at any angle from 0° (T) to 90° (R) to the growth rings (fig. 4-5). Perpendicular-to-grain properties depend sonie- what upon orientation of annual rings with respect to the direction of stress. Compres- SO'^iR) O'^iT) sion' perpendicular-to-grain values in table M 140 729 4-2 are derived from tests in which the load Figure 4f-5.—The direction of load in relation to the direction of is applied parallel to the growth rings (T- the annual growth rings: 90° or perpendicular (R); 45°; 0° or direction) ; tension perpendicular-to-grain val- parallel (T). 4-29 about the pith and by the large proportion of summerwood at the point of greatest eccen- tricity (fig. 4-6). It is more difficult to detect in lumber; however, it is usually somewhat darker because of the greater proportion of summerwood and frequently has a relatively lifeless appearance, especially in woods which normally have an abrupt transition from springwood to summerwood (fig. 4-7). Be- cause it is more opaque than normal wood, intermediate stages of compression wood can be detected by transmitted light through thin cross sections. Tension wood is more diflîcult to detect than compression wood. However, eccentric growth as seen on the transverse section frequently indicates its presence. Also, the tough tension wood fibers resist being cut cleanly and result in a woolly condition on the surfaces of sawn boards, especially when surfaced in the green condition (fig. 4-8). In some species, tension wood may show up on a smooth surface as M 28425 F areas of contrasting colors. Examples of this Figure 4—6.—The darker areas shown within the rectangle are are the silvery appearance of tension wood in compression wood. sugar maple and the darker color of tension percent greater but may be as much as 30 wood in mahogany. percent greater. Compression and tension wood undergo ex- Compression Failures cessive longitudinal shrinkage when subjected Excessive bending of standing trees from to moisture loss reaching below the fiber satu- wind or snow, trees across boulders, ration point. Longitudinal shrinkage ranges to logs, or irregularities in the ground, or the 10 times normal in compression wood and per- rough handling of logs or lumber may produce haps five times normal or more in tension excessive compression stresses along the grain wood. When present in the same board with that cause minute compression failures. In normal wood, unequal longitudinal shrinkage some instances, such failures are visible on causes internal stresses that result in warping. the surface of a board as minute lines or zones This warp sometimes occurs in rough lumber formed by the crumpling or buckling of the but more often in planed, ripped, or resawed cells (fig. 4-9A), although usually they appear lumber. Fortunately, the most serious effects only as white lines or may even be invisible occurring in pronounced compression wood to the naked eye. Their presence frequently is can be detected by ordinary visual examina- tion, as compared to borderline forms that merge with normal wood and frequently are only detected by microscopic examination. Reaction wood, particularly compression wood in the green condition, may be some- what stronger than normal wood. However, when compared to normal wood of comparable specific gravity, the reaction wood is de- finitely weaker. Possible exceptions to this are compression parallel-to-grain properties of compression wood and impact bending prop- erties of tension wood. Because of its abnormal properties, it is fre- quently desirable to eliminate reaction wood from raw material. In logs, compression wood Figure 4—7.—Sitka spruce boards containing normal wood (left) may be characterized by eccentric growth and compression wood (right).

4-30 indicated by fiber breakage on end grain (fig. 4-9B). Compression failures should not be con- fused with compression wood. Products containing visible compression failures can have seriously low strength prop- erties, especially in tensile strength and shock resistance. Tensile strength of wood containing compression failures has been found to be as low as one-third of the strength of matched clear wood. Even small compression failures, visible only under the microscope, seriously reduce strength and cause brittle fracture. Be- cause of the low strength asssociated with com- pression failures, many safety codes require certain structural members, such as ladder rails and scaffold planks, to be entirely free of them. Compression failures are often difficult to detect with the unaided eye, and special ef- forts including optimum lighting are required to aid detection. Pitch Pockets A pitch pocket is a well-defined opening that contains free resin. It extends parallel to the annual rings, and is almost flat on the pith side and curved on the bark side. Pitch pockets are confined to such species as the mi-,^7^. ¡^

:;--'/^ B

M 45594, M 81195 Figure 4-9.—A. Compression failure is shown by the Irregular lines across the grain. B. End-grain surfaces of surfaces of spruce lumber show fiber breakage caused by compression failures below the dark line.

pines, spruces, Douglas-fir, tamarack, and western larch. The effect of pitch pockets on strength de- pends upon their number, size, and location in the piece. A large number of pitch pockets indicates a lack of bond between annual growth layers, and a piece containing them should be inspected for shake or separations along the grain.

Kita Peck ■jü^lK , Maple, hickory, white ash, and a number of M 81915 F Figure 4-8.—Projecting tension wood fibers on the sawn surface other species are often damaged by small holes of a mahogany board. made by woodpeckers. These holes or bird

4-31 pecks are often placed in horizontal rows, some- or lie in the forest without serious deteriora- times encircling the tree, and a brown or black tion varies. discoloration known as a mineral streak origi- Tests on wood from trees that had stood as nates there. Holes for tapping maple trees are long as 15 years after being killed by fire also a source of mineral streaks. The streaks demonstrated that this wood was as sound are caused by oxidation and other chemical and as strong as wood from live trees. Also, changes in the wood. logs of some of the more durable species have Bird pecks and mineral streaks are not gen- had thoroughly sound heartwood after lying erally important in regard to strength, al- on the ground in the forest for many years. though they do impair the appearance of the On the other hand, decay may cause great wood. However, if several bird pecks occur in loss of strength within a very brief time, both a row across the outer surface of a piece of in trees standing dead on the stump and in wood that is to be used in a bent product, such logs cut from live trees and allowed to lie on as a handle, the holes can appreciably weaken the ground. The important consideration is not the product. whether the trees from which timber products are cut are alive or dead, but whether the Extractives products themselves are free from decay or other defects that would render them unsuit- Many species of wood contain extraneous able for use. materials or extractives that can be removed by solvents that do not degrade the cellulosic/ lignin structure of the wood. These extrac- tives are especially abundant in species such EFFECT OF MANUFACTURING AND as larch, redwood, western redcedar, and black SERVICE ENVIRONMENT ON MECHANICAL locust. PROPERTIES OF CLEAR STRAIGHT-GRAINED A small increase in modulus of rupture and WOOD in strength in compression parallel to grain has been measured for some species contain- Moisture Confenf—Drying ing extractives. The extent to which the ex- tractives influence the strength is apparently Many mechanical properties are affected by a function of the amount of extractives, the changes in moisture content below the fiber moisture content of the piece, and the mechani- saturation point. Most properties reported in cal property under consideration. tables 4-2, 4-3, and 4-4 increase with decrease in moisture content. The relation that describes these clear wood property changes in the Timber From Live Versus Dead Trees vicinity of 70° F. is: Timber from trees killed by insects, blight, wind, or fire may be as good for any struc- >— Pl2 / -Pis \ tural purpose as that from live trees, provided (v'O further insect attack, staining, decay, or sea- soning degrade has not occurred. In consider- where P is the property and M the moisture ing the subject, it may be useful to remember content in percent. Mp is the moisture content that the heartwood of a living tree is entirely at which property changes due to drying are dead, and in the sapwood only a comparatively first observed. This moisture content is slightly few cells are living. Therefore, most wood less than the fiber saturation point. (Table 4-11 is dead when cut, regardless of whether the gives values of Mp for a few species ; for other tree itself is living or not. However, if a tree species. Afp = 25 may be assumed.) stands on the stump too long after its death, Pi2 is the property value at 12 percent mois- the sapwood is likely to decay or to be attacked ture content, and ^g (green condition) is the severely by wood-boring insects, and in time property value for all moisture contents greater the heartwood will be similarly affected. Such than Mp, Average property values of P12 and P^ deterioration occurs also in logs that have are given for many species in tables 4-2, 4-3, been cut from live trees and improperly cared and 4-4. for afterwards. Because of variations in cli- The formula for moisture content adjustment matic and local weather conditions and in other is not recommended for work to maximum load, factors that affect deterioration, the length of impact bending, and tension perpendicular. the period during which dead timber may stand These properties are known to be erratic in 4-32 Table 4-11.—Moisture content at which proper- moisture content is wanted. Using information ties change due to drying for selected species from table 4-2 : Species Mp (4) Pet. Ash white 24 Birch, yellow 27 P, = 18,020 p.s.i. Chestnut, American -. 24 Douglas-fir _ _ 24 Hemlock, western 28 The increase in mechanical properties dis- Larch, western 28 cussed above assume small, clear specimens in Pine, loblolly 21 a drying process in which no deterioration of Pine, longleaf _ . 21 Pine, red 24 the product (degrade) occurs. The property Redwood . . 21 changes applied to large wood specimens such Spruce, red 27 as lumber are discussed in chapter 6. Spruce, Sitka 27 Tamarack 24 Drying degrade can take several forms. Perhaps the most common degrade is surface and end checking. Checks most often limit their response to moisture content change, often mechanical properties. Some loss of strength, apparently as a function of species. especially in shock resistance, may occur when The formula can be used to estimate a prop- wood is dried at excessively high tempera- erty at any moisture content below Mp from the tures, although visible signs of degrade may species data given. For example, suppose the not be present. modulus of rupture of white ash at 8 percent Further information is included in chapter 14.

-300 200 + 100 +200 + 300 + 400 + 500 Temperatur« ( F)

M 141 134 Figure 4-10.—The immediate effect of temperature on strength properHes, expressed as percent of value at 68° F. Trends illustrated are composites from studies on three strength properties—modulus of rupture in bending, tensile strength perpendicular to grain, and compressive strength parallel to grain—as examined by several investigators. Variability in reported results is illustrated by the width of the bands.

4-33 400

-300 200 -100 O ^100 +200 Temperature (""F)

M 141 135 Figure 4-11.—The immediate effect of temperature on the proportional limit in compression perpendicular to grain at approximately 12 percent moisture content relative to the value at 68° F. Variability in the reported results of several investigators is illustrated by the width of the band.

Temperature 4-12 illustrates the immediate effect of tempera- ture on the modulus of elasticity as a composite In general, the mechanical properties of wood of measurements made in bending, in tension decrease when heated and increase when parallel to grain, and in compression parallel cooled. This effect is immediate, but pro- to grain. Figures 4-10 through 4-12 represent longed exposure at high temperature causes an an interpretation of data from a limited number irreversible decrease in properties. of investigators. The width of the band il- At a constant moisture content and below lustrates variability between and within re- about 400° F. mechanical properties are es- ported results. The influence of moisture con- sentially linearly related to temperature. The tent is illustrated where data are available. change in properties that occurs when wood In addition to the reversible effect of tempera- is quickly heated or cooled and then tested at ture on wood, there is an irreversible effect at that condition is termed an "immediate effect." elevated temperature. This permanent effect is At temperatures below 200° F. the immediate one of degradation of wood substance, which effect is essentially reversible ; that is, the prop- results in loss of weight and strength. Quanti- erty will return to the value at the original tatively, the loss depends on factors which temperature if the temperature change is rapid. include moisture content, heating medium, Figure 4-10 illustrates the immediate ef- temperature, exposure period, and, to some fect of temperature on strength, based on a extent, species and size of piece involved. composite of tests for modulus of rupture in The decrease of modulus of rupture due to bending, tensile strength perpendicular to the heating in steam and in water is shown as grain, and compressive strength parallel to the a function of temperature and heating time grain relative to 68° F. Figure 4-11 gives in figure 4-13, based on tests of Douglas-fir similar information for proportional limit in and Sitka spruce. From the same studies work compression perpendicular to grain. Figure to maximum load was more greatly affected

4-34 than modulus of rupture by heating in water portant in analyzing the influence of tempera- (fig. 4-14). The effect of oven heating (wood ture. If the exposure is for only a short time, at 0 pet. moisture content) on the modulus of so that the inner parts of a large piece do not rupture and modulus of elasticity is shown in reach the temperature of the surrounding figures 4-15 and 4-16, respectively, as derived medium, the immediate effect on strength of from tests on four softwoods and two hard- inner parts will be less than for outer parts. woods. Note that the permanent property losses The type of loading must be considered how- discussed above are based on tests conducted ever. If the member is to be stressed in bending, after the specimens have been cooled to near the outer fibers of a piece are subjected to the 75° F. and conditioned to the range of 7 to 12 greatest load and will ordinarily govern the percent moisture content. If tested hot, presum- ultimate strength of the piece; hence, under ably immediate and permanent effects would this loading condition, the fact that the inner be additive. The extent of property loss is con- part is at a lower temperature may be of little sidered greater for hardwoods than for soft- significance. woods. For extended, noncyclic exposures, it can be Repeated exposure to elevated temperature assumed that the entire piece reaches the tem- has a cumulative effect on wood properties. perature of the heating medium and will, For example, at a given temperature the therefore, be subject to permanent strength property loss will be about the same after six losses throughout the volume of the piece, re- exposure periods of 1 month each as it would gardless of size and mode of stress applica- after a single 6-month exposure period. tion. However, wood often will not reach the The shape and size of wood pieces are im- daily extremes in temperature of the air around

180

160

12% MC

3 'S 120

c 100

e

-300 -200 + 100 + 200 Temperature (°F)

M 141 136 Figure 4-12. The Immediate effect of temperature on the modulus of elasticity, relative to the value at 68° F. The plot Is a composite of studies on the modulus as measured in bending, in tension parallel to the grain, and in compression parallel to grain by several investigators. Variability in reported results is illustrated by the width of the bands.

4-35 100

'K' a_^___^ 1 1 1 1 ^. ^¡¡^r-^^---^^^^___^^ 90 ^ — j!fA)CLqAp ^

-"^—~——^5Lai2__ 80 \ " ""^ _^^ _ \ \ BOOT. ■ \ \ 70 N _

60 -

i 50 - - I 40 - - 30 1 1 1 1 1 50 100 150 200 300 s HEATING PERIOD (DAYS) M 140 732 Figure 4-14.—Permanent effect of heating in water on work to maximum load and on modulus of rupture. Data based on tests i of Douglas-Ar and Sitka spruce.

8 16 24 32 HEATING PERIOD (HOURS) M 140 731 Figure 4-13.—Permanent effect of heating in water (solid line) and in steam (dashed line) on the modulus of rupture. Data based on tests of Douglas-fir and Sitka spruce. it in ordinary construction; thus, long-term effects should be based on the accumulated temperature experience of critical structural parts.

7/me Time—Creep/ Relaxation When first loaded, a wood member deforms elastically. If the load is maintained, additional time-dependent deformation occurs. This is called creep. Even at very low stresses, creep takes place and can continue over a period of years. For suitably high loads, failure will eventually occur. This failure phenomenon,

termed ''duration of load," is discussed in the 100 150 200 next section. TIME OF EXPOSURE (DAYS) At typical design levels the additional de- formation due to creep may approximately M 140 726 Figure 4-15.—Permanent effect of oven heating at four tempera- equal the initial, instantaneous elastic deforma- tures on the modulus of rupture, based on four softwood and tion if the environmental conditions are not two hardwood species.

4-36 laxes at a decreasing rate to about 60 to 70 percent of its original value within a few months. This reduction of stress with time is commonly termed '^relaxation." In limited bending tests carried out between approximately 65° F. and 120° F. over 2 to 3 months, the curve of stress vs. time that expresses relaxation is approximately the niir- ror image of the creep curve (deformation vs. time). These tests were carried out at stresses up to about 50 percent of the bending strength of the wood. As with creep, relaxa- tion is markedly affected by ñuctuations in temperature and humidity.

Time—Duration of Stress The duration of stress, or the time during which a load acts on a wood member, is an important factor in determining the load that a member can safely carry. For members that continuously carry loads for long periods 100 150 200 250 300 TIME OF EXPOSURE (DAYS) of time, the load required to produce failure is much less than that determined from the M 140 727 strength properties in tables 4-2, 4-3, and 4- Figure 4-16.—Permanent effect of oven heating at four tempera- 4. For example, a wood member under the tures on modulus of elasticity, based on four softwood and two continuous action of bending stress for 10 hardwood species. years will carry only about 60 percent of the load required to produce failure in the same changed. For illustration, a creep curve based specimen loaded in a standard bending strength on one species at several stress levels is shown test of only a few minutes' duration. ... , , in figure 4-17. It suggests that creep is greater 1 1 1 under higher stresses than lower ones. STRESS, RS.I. Ordinary climatic variations in temperature ^4,000 and humidity will cause creep to increase. An ^^2,000 ^S^'-" ^^^—lyOOO increase of about 50° F. in temperature can Q. ^ cause a two- to three-fold increase in creep. '^"^^^SOO ^ Ï 0 ^ 1 1 1 1 J Green wood may creep four to six times the 0 100 200 300 400 500 initial deformation as it dries under load. TIME UNDER LOAD (DAYS) M 140 725 Unloading the member results in an immedi- Figure 4-17.- -An illustration of creep as influenced by four levels ate and complete disappearance of the original of stress. (Adapted from Kingston.) elastic deformation as well as a delayed re- covery of approximately one half of the creep Conversely, if the duration of stress is very deformation. Fluctuations in temperature and short, the load-carrying capacity may be con- humidity increase the magnitude of the re- siderably higher than that determined from covered deformation. strength properties given in the tables. The Creep at low stress levels is similar m load required to produce failure in a wood bending, tension, or compression parallel to member in 1 second is approximately 25 per- grain. It is reported to be somewhat less in cent higher than that obtained in ASTM tension than in bending or compression under standard strength tests. As an approximate in- varying moisture conditions. Creep across the dication of relation of strength to duration of grain is qualitatively similar to, but likely to stress, the strength may be said to increase be greater than, creep parallel to the grain. The or decrease 7 to 8 percent as the duration of creep behavior of all species studied for creep stress is respectively decreased or increased by properties is approximately the same. a factor of 10. The duration of stress is one of If, instead of controlling load or stress, a the factors used in establishing safe allowable constant deformation is imposed and main- stresses for structural timbers; this aspect is tained on a wood member, the initial stress re- discussed in chapter 6.

4-37 Time—Fatigue direction. They may be partially or completely Fatigue in engineering material is defined reversed. Partially reversed stresses occur as the progressive damage and failure that oc- where repeated stresses are not of the same curs when a structure or part is subjected to magnitude in the two directions; fully reversed repeated loads of a magnitude smaller than the stresses are of equal magnitude, as in compres- static strength. sion and tension or as in positive and negative Fatigue should be considered in wood design shear. Fully reversed stressing is the most when repetitions of design stress or near- severe loading condition. The range ratio is design stress are expected to be more than expressed as -1 for fully reversed loading, as 100,000 cycles during the normal life of a a negative decimal for partially reversed structure. In many design considerations, the loading, and as a positive decimal for re- fatigue criteria specified will be: peated loading. Fatigue strength, fatigue life, (1) Fatigue life (the number of stress cycles and range ratio are reported for several types to be sustained), (2) range ratio (the ratio of of loading in table 4-8. minimum to maximum stress), and (3) the Tests demonstrate that specimens of clear, type of loading expected (tension parallel, straight-grained wood subjected to 2 million tension perpendicular, or flexure). The problem cycles of bending will have 60 percent of the will be to determine the greatest stress that strength of similar specimens tested under can be sustained (proportioned to fatigue static conditions. In similar fatigue tests, strength). If an indefinite fatigue life is speci- specimens with small knots (ranging from 50 fied, the fatigue limit stress should not be ex- to 90 pet. in estimated strength ratio) had 50 ceeded. This is the stress below which a ma- percent of the static strength of clear, terial can be presumed to endure an infinite straight-grained wood; specimens with 1:12 number of stress cycles. slope of grain had 45 percent of the static The repetition of fatigue stresses can take strength value. When knots and slope of grain different forms of range ratio, as from zero were both present, the specimens had approxi- to some specified stress, or from some speci- mately 30 percent of the static strength figure. fied stress value to a higher stress in the same This can be illustrated as follows:

Strength Specimen Index of Strength (Pet.) I«Heilen" (h~~ Vne" " Y - ^ ^^®^^» straight grained Fatigue (2 x 10« cycles) _ _ _ _ Clear, straight grained _ _ _ _ 100 60 zP Small knots, straight grained 50 ^. Clear, 1:12 slope of grain 45 ^" Small knots, 1:12 slope of grain 30

Time—Age and creosote, have no appreciable effect on In relatively dry and moderate temperature properties. Properties are lowered in the pres- conditions where wood is protected from de- ence of water, alcohol, or other wood-swelling teriorating influences such as decay, the me- organic liquids even though these liquids do not chanical properties of wood show little change chemically degrade the wood substance. The with time. Test results for very old timbers loss in properties largely depends on amount suggest that significant losses in strength only of swelling and this loss is regained upon re- occur after several centuries of normal aging moval of the swelling liquid. Liquid ammonia conditions. The soundness of centuries-old markedly reduces the strength and stiffness of wood in some standing trees (redwood, for wood, but most of the reduction is regained example) also attests to the durability of wood. upon removal of the ammonia. Chemical solutions that decompose wood Cfiem/ccr/s substance have a permanent effect on strength. The following generalizations summarize the The effect of chemicals on mechanical prop- effect of chemicals: (1) Some species are erties depends on the specific type of chemical. quite resistant to attack by dilute mineral and Nonswelling liquids, such as petroleum oils organic acids, (2) oxidizing acids such as 4-38 nitric acid degrade wood more than nonoxidiz- of 300 megarads, tensile strength is reduced ing acids, (3) alkaline solutions are more de- about 90 percent. Gamma rays also affect com- structive than acidic solutions, and (4) hard- pressive strength parallel to grain above 1 woods are more susceptible to attack by both megarad, but strength losses with further dos- acids and alkalies than are softwoods. Because age are less than for tensile strength. Only both species and application are extremely about one-third of the compressive strength is important, reference to industrial sources with lost when the total dose is 300 megarads. Ef- a specific history of use is recommended where fects of gamma rays on bending and shear possible. For example, large cypress tanks have strength are intermediate between the effects survived long continuous use where exposure on tensile and compressive strength. conditions involved mixed acids at the boiling point. Molding and Staining Fungi Wood products sometimes are treated with preservative or fire-retarding salts, usually in Molding and staining fungi do not seriously water solution, to impart resistance to decay or affect most mechanical properties of wood fire. Such products generally are kiln dried after because they feed upon substance within the treatment. Mechanical properties are essenti- structural cell wall rather than on the struc- ally unchanged by preservative treatment. tural wall itself. Specific gravity may be re- Properties are, however, affected to some duced by from 1 to 2 percent, while most of extent by the combined effects of fire-retardant the strength properties are reduced by a com- chemicals, treatment methods, and kiln drying. parable or only slightly greater extent. A variety of fire-retardant treatments have Toughness or shock resistance, however, may been studied. Collectively the studies indicate be reduced by up to 30 percent. The duration of modulus of rupture, work to maximum load, infection and the species of fungi involved are and toughness are reduced by varying amounts important factors in determining the extent of depending on species and type of fire retardant. weakening. Work to maximum load and toughness are Although molds and stains themselves often most affected, with reductions of as much as do not have a major effect on the strength of 45 percent. A reduction in modulus of rupture wood products, conditions that favor the de- of as much as 20 percent has been observed; velopment of these organisms are likewise ideal a design reduction of 10 percent is frequently for the growth of wood-destroying (decay) used. Stiffness is not appreciably affected by fungi, which can greatly reduce mechanical fire-retardant treatments. properties (see ch. 17). Wood is also sometimes impregnated with monomers, such as methyl methacrylate, which Decay are subsequently polymerized. Many of the properties of the resulting composite are Unlike the molding and staining fungi, the higher than those of the original wood, gen- wood-destroying (decay) fungi seriously re- erally as a result of filling the void spaces in duce strength. Even apparently sound wood ad- the wood structure with plastic. The poly- jacent to obviously decayed parts may contain merization process and both the chemical hard-to-detect, early (incipient) decay that is decidedly weakening, especially in shock re- nature and quantity of monomers are vari- sistance. ables that influence composite properties. All wood-destroying fungi do not affect wood A general discussion of the resistance of in the same way. The fungi that cause an wood to chemical degradation is given in easily recognized pitting of the wood, for chapter 3. example, may be less injurious to strength than those that, in the early stages, give a slight Nuclear Radiation discoloration of the wood as the only visible effect. Very large doses of gamma rays or neutrons No method is known for estimating the can cause substantial degradation of wood. In amount of reduction in strength from the general, irradiation with gamma rays in doses appearance of decayed wood. Therefore, when up to about 1 megarad has little effect on the strength is an important consideration, the strength properties of wood. As dosage in- safe procedure is to discard every piece that creases above 1 megarad, tensile strength paral- contains even a small amount of decay. An lel to grain and toughness decrease. At a dosage exception may be pieces in which decay occurs

4-39 in a knot but does not extend into the surround- ing wood. powderpost larvae, by their irregular burrows, may destroy most of the interior of a piece, Insect Damage while the surface shows only small holes, and the strength of the piece may be reduced virtu- Insect damage may occur in standing trees, ally to zero. logs, and unseasoned or seasoned lumber. Dam- No method is known for estimating the age in the standing tree is difficult to con- amount of reduction in strength from the ap- trol, but otherwise insect damage can be pearance of insect-damaged wood, and, when largely eliminated by proper control methods. strength is an important consideration, the Insect holes are generally classified as pin- safe procedure is to eliminate pieces contain- holes, grub holes, and powderpost holes. The ing insect holes.

BIBLIOGRAPHY American Society for Testing and Materials Kukachka, B. F. Standard methods for testing small clear specimens 2i.,^i?^ber. D 143. (See current edition.) 1970. Properties of imported tropical woods. Philadelphia, Pa. USDA Forest Serv. Res. Pap. FPL 125. Forest Prod. Lab., Madison, Wis. ^^n^^tsen, B A., Preese, Frank, and Ethington, R. L. Little, E. L. Jr. 1970. Methods for sampling clear, straight-grained 1953. Checklist of native and naturalized trees of wood from the forest. Forest Prod. J the United States. USDA Agr. Handbook 20(11) : 38-47. 41. 472 pp. Boiler, K. H. MacLean, J. D. 1954. Wood at low temperatures. Modern Packag- ing 27(9). ^ 1953. Effect of steaming on the strength of wood. Coffey,D.J. Amer. Wood-Preservers Assoc. 49: 88-112. 1962. EflPects of knots and holes on the fatigue 1954. Effect of heating in water on the strength strength of quarter-scale timber bridge stringers. M.S. Thesis, Civil Eng., Univ. of properties of wood. Amer. Wood-Pre- Wisconsin. servers Assoc. 50: 253-281. Comben, A. J. Millett, M. A., and Gerhards, C. C. 1972. Accelerated aging: Residual weight and 1964. The effect of low temperatures on the flexural properties of wood heated in air strength and elastic properties of timber. ,, , at 115° to 175° C. Wood Sei. 4(4). r.n J T. ,J^^^- Inst- Wood Sei. 13: 44-55. (Nov.) Ellwood, E. L. Munthe, B. P., and Ethington, R. L. 1968. Method for evaluating shear properties of 1954. Properties of American beech in tension and wood. USDA Forest Serv. Res. Note compression perpendicular to the grain FPL-0195. Forest Prod. Lab., Madison, and their relation to drying. Yale Univ. Wis. Bull. 61. Pillow, M. Y. Fukuyama, M., and Takemura, T. 1949. Studies of compression failures and their 1962. The effects of temperature on compressive detection in ladder rails. Forest Prod. Lab. properties perpendicular to grain of wood. Rep. D 1733. Jour. Jap. Wood Res. Soc. 8(4). Schaffer, E. L. , and Takemura, T. 1970. Elevated temperature effect on the longitudi- 1962. The effect of temperature on tensile proper- nal mechanical properties of wood. Ph.D. ties perpendicular to grain of wood. Jour. thesis. Univ. of Wis. Jap. Wood Res. Soc. 8(5). Sulzberger, P. H. Gerhards, C. C. 1953. The effect of temperature on the strength 1968. Effects of type of testing equipment and of wood, plywood and glued joints. Asst. specimen size on toughness of wood. TT r. ^ ^^^^' ^^s- Co^s- Comm. Rep. ACA-46. USDA Forest Serv. Res. Pap. FPL 97. U.S. Department of Defense Forest Prod. Lab., Madison, Wis. 1951. Design of wood aircraft structures. ANC-18 Hearmon, R. F. S. Bull. (Issued by Subcommittee) on Air- n.d. Applied anisotropic elasticity. Pergamon Force-Navy-Civil Aircraft. Design Cri- Press, London. teria Aircraft Comm.) 2nd ed. Munitions Kingston, R. S. T. , ^^^- Aircraft Comm. 234 pp., illus. Wangaard, F. F. 1962. Creep, relaxation, and failure of wood. Res. App. in Ind. 15(4). 1966. Resistance of wood to chemical degradation. Forest Prod. J. 16(2) : 53-64. Kollmann, Franz F. P., and Côté, Wilfred A. Jr. Youngs, R. L. 1968. Principles of wood science and technology. 1957. Mechanical properties of red oak related to Springer Verlag, New York. drying. Forest Prod. J. 7(10): 315-324.

APPENDIX In this appendix, tables 4-2, 4-3, and 4-4 Practice Guide, E 380-72, where the newton is have been rewritten in SI or metric units, and the basic measure of force, the pascal that of thus appear as tables A-4-2, A-4-3, and A-4-4. stress, the meter that of length, and the The units used follow the ASTM Metric joule that of energy. 4-40 0 0 ô 0 00 00 00 OQ 00 00 0 ô 00 00 00 00 00 ÇO 0 0 0 0 §§ : 10 (M CO Ci co«r> THOO 0000 loocoLoißco

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Static bending Compres- Compres- Shear DoTTunon "names Specific sion sion parallel of species gravity Modulus of Modulus of parallel perpen- to grain— rupture elasticity to grain— dicular maximum maximum to grain— shearing crushing fiber strength strength stress at pro- por- tional limit Kilo- Mega- Kilo- Kilo- Kilo- pascals pascals pascals pascals pascals HARDWOODS Aspen: Quaking f 0.37 38,000 9,000 16,200 1,400 5,000 68,000 11,200 36,300 3,500 6,800 Big-toothed Í .39 36,000 7,400 16,500 1,400 5,400 66,000 8,700 32,800 3,200 7,600 Cottonwood : Black Í .30 28,000 6,700 12,800 700 3,900 49,000 8,800 27,700 1,800 5,900 Eastern / .35 32,000 6,000 13,600 1,400 5,300 52,000 7,800 26,500 3,200 8,000 Balsam, poplar / «37 34,000 7,900 14,600 1,200 4,600 70,000 11,500 34,600 2,900 6,100 SOFTWOODS

Cedar : Alaska- Í -42 46,000 9,200 22,300 2,400 6,100 80,000 11,000 45,800 4,800 9,200 Northern white- Í .30 27,000 3,600 13,000 1,400 4,600 42,000 4,300 24,800 2,700 6,900 Western redcedar Í «31 36,000 7,200 19,200 1,900 4,800 54,000 8,200 29,600 3,400 5,600 Douglas-fir f -45 52,000 11,100 24,900 3,200 6,300 88,000 13,600 50,000 6,000 9,500 Fir: Subalpine Í .33 36,000 8,700 17,200 1,800 4,700 56,000 10,200 36,400 3,700 6,800

Pacific silver Í .36 38,000 9,300 19,100 1,600 4,900 69,000 11,300 40,900 3,600 7,500

Balsam Í -34 36,000 7,800 16,800 1,600 4,700 59,000 9,600 34,300 3,200 6,300 Hemlock : Eastern f -40 47,000 8,800 23,600 2,800 6,300 67,000 9,700 41,200 4,300 8,700

Western f .41 48,000 10,200 24,700 2,600 5,200 81,000 12,300 46,700 4,600 6,500

Larch, western / «^^ 60,000 11,400 30,500 3,600 6,300 107,000 14,300 61,000 7,300 9,200 4-49 Table A-4-3.—Mechanical properties of some commercially/ important woods grown in Canada and imported into the United States ^—continued

Static bending Compres- Compres- Shear Common names Specific sion sion parallel of species gravity Modulus of Modulus of parallel perpen- to grain— rupture elasticity to grain— dicular maximum maximum to grain— shearing crushing fiber strength strength stress at pro- por- tional limit Kilo- Mega- Kilo- Kilo- Kilo- pascals pascals pascals pascals pascals SOFTWOODS—continued

Pine: Eastern white f »^^ 35,000 8,100 17,900 1,600 4,400 66,000 9,400 36,000 3,400 6,100 Jack r .42 43,000 8,100 20,300 2,300 5,600 78,000 10,200 40,500 5,700 8,200 Lodgepole / '40 39,000 8,800 19,700 1,900 5,000 76,000 10,900 43,200 3,600 8,500 Ponderosa f -44 39,000 7,800 19,600 2,400 5,000 73,000 9,500 42,300 5,200 7,000 Red r .39 34,000 7,400 Í6,300 1,900 4,900 70,000 9,500 37,900 5,000 7,500 Western white f .36 33,000 8,200 17,400 1,600 4,500 64,100 10,100 36,100 3,200 6,300 Spruce: Black I .41 41,000 9,100 19,000 2,100 5,500 79,000 10,500 41,600 4,300 8,600 Engelmann f -38 39,000 8,600 19,400 1,900 4,800 70,000 10,700 42,400 3,700 7,600 Red I .38 41,000 9,100 19,400 1,900 5,600 71,000 11,000 38,500 3,800 9,200 Sitka I .35 37,000 9,400 17,600 2,000 4,300 70,000 11,200 37,800 4,100 6,800 White ^ I .35 35,000 7,900 17,000 1,600 4,600 63,000 10,000 37,000 3,400 6,800 Tamarack Í .48 47,000 8,600 21,600 2,800 6,300 76,000 9,400 44,900 6,200 9,000

^Results of tests on small, clear, straight-grained ^ The values in the first line for each species are from specimens. Property values based on American Society tests of green material; those in the second line are for Testing and Materials Standard D 2555-70, "Stand- adjusted from the green condition to 12 pet. moisture ard methods for establishing clear wood values." content using dry to green clear wood property ratios Information on additional properties can be obtained as reported in ASTM D 2555-70. Specific gravity is from Department of Forestry, Canada, Publication No. based on weight when ovendry and volume when green. 1104.

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Chapter 5

COMMERCIAL LUMBER

Page Hardwood Lumber 5-2 Factory Grades 5-2 Cutting Grades 5-2 Dimension Parts 5-5 Finished Market Products 5-5 Hardwood Lumber Species 5-8 Softwood Lumber 5-9 Softwood Lumber Grades 5-9 Softwood Lumber Manufacture 5-11 Softwood Lumber Species 5-15 Softwood Lumber Grading 5-16 Purchasing Lumber 5-16 Lumber Distribution 5-16 Retail Yard Inventory 5-16 Important Purchase Considerations 5-19 Standard Lumber Abbreviations 5-20 Bibliography 5-21

5-1 COMMERCIAL LUMBER

A log when sawed yields lumber of varying Factory Grades quality. The objective of grading is to enable a user to buy the quality that best suits his The rules adopted by the National Hardwood purpose. This is accomplished by dividing the Lumber Association are considered standard in lumber from the log into use categories, each grading hardwood lumber for cutting into having an appropriate range in quality. smaller pieces to make furniture or other fab- Except as noted later, the grade of a piece ricated products. In these rules the grade of a of lumber is based on the number, character, piece of hardwood lumber is determined by and location of features that may lower the the proportion of a piece that can be cut strength, durability, or utility value of the into a certain number of smaller pieces of ma- lumber. Among the more common visual fea- terial generally clear on one side and not tures are knots, checks, pitch pockets, shake, smaller than a specified size. In other words, and stain, some of which are a natural part the grade classification is based upon the of the tree. Some grades are free or practically amount of usable lumber in the piece rather free from these features. Other grades com- than upon the number or size of growth fea- prising the great bulk of lumber contain fairly tures that characterize softwood grades. This numerous knots and other features that may usable material, commonly termed 'cuttings," affect quality. With proper grading, lumber con- must have one face clear and the reverse face taining these features is entirely satisfactory sound, which means free from such things as for many uses. wane, rot, pith, and shake that materially im- The principal grading operation for most pair the strength of the cutting. The lowest lumber takes place at the sawmill. Establish- cutting grades require only that the cuttings be ment of grading pirocedures is largely the sound. responsibility of manufacturing associations. Because of the wide variety of wood species, Cutting Grades industrial practices, and customer needs, dif- ferent lumber grading practices coexist. The The highest cutting grade is termed "Firsts" grading practices of most interest are con- and the next grade ''Seconds." First and Sec- sidered in the sections that follow, under the onds are nearly always combined in one grade major categories of Hardwood Lumber and and referred to as "FAS." The third grade Softwood Lumber. is termed "Selects" followed by No. 1 Common, No. 2 Common, Sound Wormy, No. 3A Com- mon, and No. 3B Common. A description of the HARDWOOD LUMBER standard hardwood cutting grades is given in table 5-1. This table illustrates, for example, Hardwood lumber is graded according to that Firsts call for pieces that will allow 91% three basic marketing categories: Factory percent of their surface measure to be cut Lumber, Dimension Parts, and Finished Mar- into clear face material. Not more than 8% per- ket Products. Both factory lumber and dimen- cent of each piece can be wasted in making the sion parts are intended to serve the industrial required cuttings. In general the minimum ac- customer; the important difference is that ceptable length, width surface measure, and the factory lumber grades reflect the propor- percent of piece that must work into a cut- tion of a piece that can be cut into useful ting decreases with decreasing grade. The smaller pieces while the dimension grades are grade of hardwood lumber called "Sound based on use of the entire piece. Finished Wormy" has the same requirements as No. 1 market products are graded for their unique Common and Better except that wormholes and end use with little or no remanufacture. Ex- limited sound knots and other imperfections amples of finished products include molding, are allowed in the cuttings. Figure 5-1 is an stair treads, and hardwood flooring. illustration of grading for cuttings.

5-2 Table 5-1.—Standard hardwood cutting grades

Amount of each piece Grade and lengths allowed Widths Surface measure that must Maximum Minimum size of (feet) allowed of pieces work into cuttings cuttings required clear-face allowed cuttings In. Sqjt. Pet Number Firsts:' 8 to 16 (will admit 30 per- 4 to 9 __ 1 cent of 8- to 11-foot, Vz of 91 % 4 inches by 5 feet, or 6 + 10 to 14 91% 2 which may be 8- and 9- 15+ ___- 3 inches by 7 feet foot.) ^ 91% 3 4 and 5 _ 83% 1 Seconds : * 6 and 7 _ 831/3 1 8 to 16 (will admit 30 per- 6 and 7 . 91% 2 cent of 8- to 11-foot, Vz of 6-f 8 to 11 _ 83% 2 which may be 8- and 9- 8 to 11 _ 91% 3 Do. foot). 12 to 15 83 Vs 3 12 to 15 91% 4 16+ _--_ 831/3 4 Selects : 6 to 16 (will admit 30 per- 2 and 3 cent of 6- to 11-foot, % of 91% Do. which may be 6-» and 7- 4 + 4+ ____ (3) } foot).

1 100 0 2 75 1 No. 1 Common: 3 and 4 _ 1 4 to 16 (will admit 10 per- 3 and 4 _ 75 2 cent of 4- to 7-foot, Vz of 3 + 5 to 7 _ 2 4 inches by 2 feet, or which may be 4- and 6- 5 to 7 ._ 75 3 3 inches by 3 feet foot). 8 to 10 __ 66% 3 11 to 13 66% 4 14+ ____ 66% 5

66% 1 2 and 3 _-- 50 1 2 and 3 _. 66% 2 No. 2 Common : 4 and 5 _. 50 2 4 to 16 (will admit 30 per- 4 and 5 _. m% 3 cent of 4- to 7-foot, % of 6 and 7 _ 50 3 3 inches by 2 feet which may be 4- and 5- 3 + 6 and 7 _. 66% 4 foot). J 8 and 9 _. 50 4 10 and 11 50 5 12 and 13 . 50 6 14+ 50 7 No. 3 A Common : 4 to 16 (will admit 50 per- cent of 4- to 7-foot, l^ of which may be 4- and 5- ^ + 1 + ^331/3 (5) Do. foot). No. 3B Common : 4 to 16 (will admit 50 per- cent of 4- to 7-foot, V2 of 1 % inches by 2 feet which may be 4- and 5- 3 + 1 + '25 (5) foot). J

^ Inspection to be made on the poorer side of the ' Same as Seconds with reverse side of board not be- piece, except in Selects. low No. 1 Common or reverse side of cuttings sound. ' Firsts and Seconds are combined as 1 grade (FAS). * This grade also admits pieces that grade not below The percentage of Firsts required in the combined No. 2 Common on the good face and have the reverse grade varies from 20 to 40 percent, depending on the face sound. species. ^ Unlimited. * The cuttings must be sound ; clear face not required.

5-3 ^-^ CUTTING NO. 1-3 1/2" X 4 1/2'= 15 3/4 UNITS CUTTING NO. 3-4 l/2"X4 l/2'= 20 1/4 UNITS

CUTTING NO. 2-8 1/2' X4 1/2 =38 1/4 UNITS <9 CUTTING NO. 4-6" X 5 2/3' = 34 UNITS

1. Determine Surface Measure (S.M.) using lumber 5. Determine clear-face cutting units needed. scale stick or from formula: For No. 1 Common grade S.M. x 8 = 12 x 8 « 96 units. Width in inches x length in feet ^ 12" x 12' 12 " 12 = 12 sq. ft. S.M. Determine total area of permitted clear-face cutting in units.

2. No. 1 Common is assumed grade pf board. Width in inches and fractions of inches Percent of clear-cutting area required for x length in feet and fractions of feet. No. 1 Common—66-2/3% or 8/12. Cutting //I—3-1/2" X 4-1/2' = 15-3/4 units Cutting //2—8-1/2" X 4-1/2' = 38 units 3. Determine maximum number of cuttings Cutting //3~4-l/2" X 4-1/2' = 20-1/4 units permitted. Cutting /'4—6" X 5-2/3' = 34 units

For No. 1 Common grade (S.M. + 1) v 3 Total Units 108

- (12 +1) = 13 = 4, cuttings. Units required for No. 1 Common—96.

Determine minimum size of cuttings. 7. Conclusion: Board meets requirements for No. 1 Common grade. For No. 1 Common grade 4" x 2' or 3" X 3'. M 139 690 Figure 5-1.—An example of hardwood grading for cuttings using a No. 1 Common factory grade.

This brief summary of the factory grades grades do specify minimum widths for each should not be regarded as a complete set of grade as follows: grading rules, as numerous details, exceptions, Firsts 6 inches and special rules for certain species are not Seconds _ 6 inches included. The complete official rules of the Na- Selects _ 4 inches tional Hardwood Lumber Association should be Nos. 3, 2, 3A, 3B Common 3 inches followed as the only full description of exist- If width is specified by purchase agreement, ing grades. SIE or S2E lumber is % inch scant of nominal in lumber less than 8 inches wide and % inch Cutting Sizes scant in lumber 8 inches and wider. Standard lengths Standard lengths are 4, 5, 6, 7, 8, 9, 10, 11, Table 5-2.—Standard thickness for rough and 12, 13, 14, 15, and 16 feet, but not more than surfaced (S2S) hardwood lumber 50 percent of odd lengths are allowed in any single shipment. Rough Surfaced Rough Surfaced Standard thickness In. In. In. In. Standard thicknesses for hardwood lumber, % •Tie 2% 21/4 rough and surfaced (S2S), are given in table 1/2 S/lR 3 2% % %fi 31/2 31/+ 5-2. The thickness of SIS lumber is subject to % %6 4 3 % contract agreement. 1 13/16 4% (') 1% IVie 5 (') Standard widths ly. l¥l6 51/2 (') 1 % 1% 6 D Hardwood lumber is usually manufactured 2 1% to random width. The hardwood factory grades ^ Finished size not specified in rules. Thickness sub- do not specify standard widths; however, the ject to special contract. 5-4 Species Graded by Hardwood Factory Grades' Other examples are , siding, ties, planks, carstock, construction boards, timbers, trim, Alder, red Hardwoods (Tropical Ash American other than molding, stair treads, and risers. Grading rules Aspen mahogany and Spanish promulgated for flooring anticipate final con- Basswood cedar) sumer use and are summarized in this section. Beech Hickory Birch Locust Details on grades of other finished products Boxelder Magnolia are found in appropriate association grading Buckeye Mahogany Butternut African rules. Cedar, aromatic red Cuban and San Hardwood flooring generally is graded un- Cedar, Spanish- Dominican der the rules of the Maple Flooring Manufac- Cherry Philippine Chestnut Maple : turers Association and the rules of the Cottonwood Hard (or sugar) National Oak Flooring Manufacturers Associa- Cypress Soft tion. Tongued-and-grooved and end-matched Elm: Pacific Coast Rock (or cork) Oak: hardwood flooring is commonly furnished. Soft Red Square edge and square end strip flooring is Gum: White also available as well as parquet flooring suit- Black Pecan Red and sap Poplar able for laying on a base or on an or- Tupelo Sycamore dinary subfloor. Hackberry Walnut Hardwoods (Philippine) Willow The Maple Flooring Manufacturers Associa- tion grading rules cover flooring manufactured from hard maple, beech, and birch. Each spe- cies is graded into four categories—First Dimension Parts grade, Second grade. Third grade, and Hardwood dimension parts are generally Fourth grade. Combination grades of Second graded under the rules of the Hardwood and Better and Third and Better are sometimes Dimension Manufacturers Association. Dimen- specified. There are also three special grades— sion signifies primarily that the stock is proc- Selected First grade light northern hard maple. essed so it can be used virtually in the sizes Selected First grade amber northern hard maple. Selected First grade red (produced from provided. Hardwood dimension rules encompass three northern beech or birch) which are made up of classes of material: Solid dimension flat stock, special stock selected for color. kiln-dried dimension flat stock, and solid di- First grade flooring must have one face prac- mension squares. Each class may be rough, tically free from all imperfections. Variations semifabricated, or fabricated. Rough dimension in the natural color of the wood are allowed. blanks are usually kiln dried and are supplied Second grade flooring admits tight, sound sawn and ripped to size. Surfaced or semi- knots and other slight imperfections but must fabricated stock has been further processed by lay without waste. Third grade flooring has gluing, surfacing, tenoning, etc. Fabricated few restrictions as to imperfections in the stock has been completely processed for the grain but must permit proper laying and pro- end use. Solid dimension flat stock has five vide a good, serviceable floor. grades: Clear—two faces, clear—one face, The standard thickness of maple, beech, and paint, core, and sound. Squares have three birch flooring is ^%2 inch. Face widths are 1%, grades if rough (clear, select, sound) and four 2, 2%, and 3^4 inches. Standard lengths are 2 if surfaced (clear, select, paint, second). feet and longer in First and Second grade flooring and IV^ feet and longer in Third grade Finished Market Products flooring. Some hardwood lumber products are graded The grading rules of the National Oak Floor- in relatively finished form, with little or no ing Manufacturers Association mainly cover further processing anticipated. Flooring is quartersawed and plain-sawed oak flooring. probably the highest volume finished product. Quartersawed flooring has two grades—Clear and Select. Plainsawed flooring has four grades—Clear, Select, No. 1 Common, and No. ^ Species names are those used in grading rules of the National Hardwood Lumber Association. Two 2 Common. The Clear grade in both plain- woods—cedar (eastern redcedar, known as aromatic sawed and quartersawed flooring must have the red) and cypress (baldcypress)—are not hardwoods. face free from surface imperfections except for Cypress lumber has a different set of grading rules from those used for the hardwoods. three-eighths inch of bright sap. Color is not 5-5 Table 5-3.—Nomenclature for some types of hardwood lumber

Commercial name Official common Botanical name for lumber tree name Alder, red Red alder A Inns rubra Ash: Black Black ash Fraxintis nigra Oregon Oregon ash F, latifolia r Blue ash F. quadrangulata White s Green ash F. pennsylvanica I White ash F. americana Aspen (popple) _ / Bigtooth aspen Populus grandidentata ^ Quaking aspen P. tremuloides Basswood _ _/ American basswood Tilia americanxi __<^ White basswood T. heterophylla Beech Beech Fagus gravdifolia Gray birch Betula populifolia Paper birch B. papyrifera Birch River birch B, nigra Sweet birch B, lenta Yellow birch B, alleghaniensis Box elder Boxelder Acer negundo Buckeye __/ Ohio buckeye Aesculus glabra ^ Yellow buckeye A, octandra Butternut _ Butternut Juglans cinérea Cherry Black cherry _ _ Prunus serótina Chestnut Chestnut Castanea dentata f Balsam poplar Populus balsamifera Cottonwood < Eastern cottonwood P. deltoides I Plains cottonwood F. sargentii Cucumber Cucumbertree Magnolia acuminata Dogwood _ / Flowering dogwood Cornue florida I Pacific dogwood C. nuttallii Elm: {Cedar elm . Ulnvus crassifolia Rock elm U. thomasii September elm U. serótina Winged elm C7. alata Soft American elm JJ, americana Slippery elm U, rubra Gum _ _ _ Sweetgmn _ Liquidambar styracifltm Hackberry _ _ / Hackberry Celtis ocddentalis \ Sugarberry C. laevigata I Mockernut hickory Hickory \ Pignut hickory _ C. glabra I Shagbark hickory C. ovata I Shellbark hickory C. laciniosa Holly American holly Ilex opaca Ironwood Eastern hophornbeam Ostrya virginiana Locust / Black locust Robinia pseudoacacia Honeylocust _ Gleditsia triacanthos Madrone Pacific madrone Arbutus menziesii Magnolia / Southern magnolia Magnolia grangrandiflora Sweetbay M, virginiana

5-6 Table 5-3.—Nomenclature for some types of hardwood lumber—continued

Commercial name Official common Botanical name for lumber tree name Maple : Black maple Acer nigrum Hard | Sugar maple A. saccharum Oregon Big leaf maple A. macrophyllum Red maple A, rubrum Soft I Silver maple A, saccharinum Oak: Black oak Quercus velutina Blackjack oak _-_ Q. marilandica California black oak Q. kelloggi Cherrybark oak Q. falcata var. pagodaefolia Laurel oak Q. laurifolia Northern pin oak Q. ellipsoidalis Northern red oak Q. rubra Red Nuttall oak Q. nuttallii Pin oak Q. palustris Scarlet oak Q. coccínea Shumard oak Q. shumardii Southern red oak Q. falcata Turkey oak Q. laevis Willow oak Q. phellos Arizona white oak Q. arizonica Blue oak Q. douglasii Bur oak Q. macrocarpa California white oak Q. lobata Chestnut oak Q. primus Chinkapin oak Q. muehlenbergii Emory oak Q. emoryi White Gambel oak Q. gambelii Mexican blue oak Q. oblongifolia Live oak Q. virginiana Oregon white oak Q. garryana Overcup oak Q. lyrata Post oak Q. stellata Swamp chestnut oak Q. michauxii Swamp white oak _ Q. bicolor White oak Q. alba Oregon myrtle California-laurel Umbellularia califomica Osage orange (bois d'arc) Osage-orange Madura pomifera Bittemut hickory Gary a cordiformis Nutmeg hickory C. myristicaeformis Pecan Water hickory C. aquatica Pecan C illinoensis Persimmon Common persimmon Diospyros virginiana Poplar Yellow-poplar Liriodendron tulipifera Sassafras Sassafras Sassafras albidum Sycamore American sycamore Platanv^ ocddentalis

Black túpelo Nyssa sylvatica Tupelo Ogeechee túpelo N. ogeche Water túpelo N, aquatica Walnut Black walnut Juglans nigra Black willow Salix nigra Willow Peachleaf willow S. amygdaloides

5-7 considered in the Clear grade. Select flooring practically clear with an all-bright sapwood (plain-sawed or quartersawed) may contain face; Second grade, admits sound tight knots, sap and will admit a few features such as pin pm wormholes, streak, and slight machining wormholes and small tight knots. No. 1 Com- imperfections; Second grade red, similar to mon plain-sawed flooring must contain mate- Second grade but must have a heartwood face ; rial that will make a sound floor without cut- Third grade, must make a sound floor without ting. No. 2 Common may contain grain and cutting; and Fourth grade, must provide a serv- surface imperfections of all kinds but must pro- iceable floor. The standard sizes for pecan floor- vide a serviceable floor. ing are the same as those for oak flooring. Standard thicknesses of oak flooring are 25/32, The National Oak Flooring Manufacturers 1/2, and % inch. Standard face widths are l^i, Association rules for hard maple, beech, and 2, 214, and 314 inches. lengths in upper grades birch flooring are the same as those of the are 2 feet and up with a required average of Maple Flooring Manufacturers Association. 414 feet in a shipment. In the lower grades lengths are m feet and up with a required average of 21/2 or 3 feet per shipment. Hardwood Lumber Species A voluntary commercial standard (CS 56) has been in effect for oak flooring since 1936, The names used by the trade to describe being revised periodically. commercial lumber in the United States are The rules of the National Oak Flooring Man- not always the same as the names of trees ufacturers Association also include specifica- adopted as official by the USDA Forest Service. tions for flooring of pecan, hard maple, beech, Table 5-3 shows the common trade name, the and birch. The grades of pecan flooring are: USDA Forest Service tree name, and the botan- First grade, practically clear but unselected ical name. Table 5-4 lists United States agen- for color; First grade red, practically clear cies and associations that prepare rules for and with an all-heartwood face ; First grade white. supervise grading of hardwoods.

Table 5-4.—Hardwood grading associations in United States Name and Address Species Covered by Grading Rules National Hardwood Lumber Association Hardwoods (furniture cuttings, construction 59 East Van Buren Street lumber, siding, panels) Chicago, Illinois 60605

Hardwood Dimension Manufacturers Hardwoods (hardwood furniture dimension, squares, Association laminated stock, interior trim, stair treads and 3813 Hillsboro Road risers) Nashville, Tennessee 37215

Maple Flooring Manufacturers Association Maple, beech, birch (flooring) 424 Washington Avenue, Suite 104 Oshkosh, Wisconsin 54901

National Oak Flooring Manufacturers Oak, pecan, beech, birch, and hard maple Association (flooring) 814 Sterick Building Memphis, Tennessee 38103

Northern Hardwood and Pine Manufacturers Aspen (construction lumber—see discussion Association Softwood Lumber Grading) Suite 207, Northern Building Green Bay, Wisconsin 54301

5-8 SOFTWOOD LUMBER after primary processing (sawing and plan- ing) . Remanufacture refers to lumber that will undergo a number of further manufacturing Softwood lumber for many years has demon- steps and reach the consumer in a significantly strated the versatility of wood by serving as a different form. primary raw material for construction and manufacture. In this role it has been produced in a wide variety of products from many differ- ent species. The first industry-sponsored grad- Lumber for Construction ing rules (product descriptions) for softwoods were established before 1900 and were com- The grading requirements of construction paratively simple because the mar- lumber are related specifically to the major keted their lumber locally and grades had only construction uses intended and little or no local significance. As new timber sources were further grading occurs once the piece leaves developed and lumber was transported to dis- the sawmill. Construction lumber can be placed tant points, each producing region continued in three general categories—stress-graded, to establish its own grading rules, so lum- nonstress-graded, and appearance lumber. ber from various regions differed in size, grade Stress-graded and nonstress-graded lumber are name, and permitted grade characteristics. employed where the structural integrity of the When different species were graded under dif- piece is the primary requirement. Appearance ferent rules and competed in the chief consum- lumber, as categorized here, encompasses ing areas, confusion and dissatisfaction were those lumber products in which appearance is inevitable. of primary importance; structural integrity, To eliminate unnecessary differences in the while sometimes important, is a secondary fea- grading rules of softwood lumber and to im- ture. prove and simplify these rules, a number of conferences were organized from 1919 to 1925 Stress-graded lumber by the U.S. Department of Commerce. These were attended by representatives of lumber Almost all softwood lumber nominally 2 to 4 manufacturers, distributors, wholesalers, re- inches thick is stress graded under the na- tailers, engineers, architects, and contractors. tional grading rules promulgated within the The result was a relative standardization of American Softwood Lumber Standard. For sizes, definitions, and procedures for deriving lumber of this kind there is a single set of properties, formulated as a voluntary American grade names and descriptions used through- Lumber Standard. This standard has been mod- out the United States. Other stress-graded ified several times since. The current edition of products include timbers, posts, stringers, the standard is issued in pamphlet form as the beams, decking, and some boards. Stress grades American Softwood Lumber Standard PS 20- and the National Grading Rule are discussed 70. in chapter 6. Softwood lumber is classified for market use by form of manufacture, species, and grade. Nonstress-graded lumber For many products the American Softwood Lumber Standard serves as a basic reference. Traditionally, much of the lumber intended For specific information on other products, for general building purposes with little or no reference must be made to industry marketing remanufacture has not been assigned allowable aids, trade journals, and grade rules. The fol- properties (stress graded). This category of lowing sections outline general classifications lumber has been referred to as yard lumber; of softwood lumber. however, the assignment of allowable proper- ties to an increasing number of former "yard" items has diluted the meaning of the term yard lumber. Soffwood Lumber Grades In nonstress-graded structural lumber, the section properties (shape, size) of the pieces Softwood lumber grades can be considered combine with the visual grade requirements to in the context of two major categories of provide the degree of structural integrity in- use: (1) Construction and (2) remanufac- tended. Typical nonstress-graded items include ture. Construction relates principally to lum- boards, lath, , crossarms, planks, and ber expected to function as graded and sized foundation stock.

5-9 Boards, sometimes referred to as "commons," definitions of letter grades.) Appearance are one of the more important nonstress-graded grades are also often known as "Select" products. Common grades of boards are suit- grades. Descriptive terms such as "prime" and able for construction and general utility pur- "clear" are applied to a limited number of spe- poses. They are separated into three to five cies. The specification FG (flat grain), VG different grades depending upon the species (vertical grain), or MG (mixed grain) is of- and lumber manufacturing association in- fered as a purchase option for some appear- volved. Grades may be described by number ance lumber products. In cedar and redwood, (No. 1, No. 2) or by descriptive terms (Con- where there is a pronounced difference in color struction, Standard). between heartwood and sapwood and heart- Since there are differences in the inherent wood has high natural resistance to decay, properties of the various species and in corre- grades of heartwood are denoted as "heart." sponding names, the grades for different spe- In some species and products two, or at most cies are not always interchangeable in use. three, grades are available. A typical example First-grade boards are usually graded primar- is casing and base in the grades of C&BTR ily for serviceability, but appearance is also and D in some species and in B&BTR, considered. This grade is used for such pur- C,C&BTR, and D in other species. Although poses as siding, cornice, shelving, and panel- several grades may be described in grade ing. Features such as knots and knotholes are rules, often fewer are offered on the retail mar- permitted to be larger and more frequent as ket. the grade level becomes lower. Second- and Grade B&BTR allows a few small imperfec- third-grade boards are often used together for tions, mainly in the form of minor skips in such purposes as subfloors, roof and wall manufacture, small checks or stains due to sheathing, and rough concrete work. Fourth- seasoning, and, depending on the species, small grade boards are not selected for appearance pitch areas, pin knots, or the like. Since ap- but for adequate strength. They are used for pearance grades emphasize the quality of one roof and wall sheathing, subfloor, and rough face, the reverse side may be lower in quality. concrete form work. In construction, grade C&BTR is the grade Grading provisions for other nonstress- combination most commonly available. It is graded products vary by species, product, and used for high-quality interior and exterior grading association. Lath, for example, is avail- trim, paneling, and cabinetwork, especially able generally in two grades. No. 1 and No. where these are to receive a natural finish. It 2; one grade of is listed in one grade is the principal grade used for flooring in rule and six in another. For detailed descrip- homes, offices, and public buildings. In indus- tions it is necessary to consult the appropriate trial uses it meets the special requirements for grade rule for these products. large sized, practically clear stock. The number and size of imperfections per- Appearance lumber mitted increases as the grades drop from B&BTR to D and E. Appearance grades are not Appearance lumber often is nonstress-graded uniform across species and products, however, but forms a separate category because of the and official grade rules must be used for de- distinct importance of appearance in the grad- tailed reference. C is used for many of the ing process. This category of construction lum- same purposes as B&BTR, often where the ber includes most lumber worked to a pattern. best paint finish is desired. Grade D allows Secondary manufacture on these items is usu- larger and more numerous surface imperfec- ally restricted to onsite fitting such as cutting tions that do not detract from the appearance to length and mitering. There is an increas- ing trend toward prefinishing many items. The of the finish when painted. Grade D is used in appearance category of lumber includes trim, finish construction for many of the same uses siding, flooring, ceiling, paneling, casing, base, as C. It is also adaptable to industrial uses stepping, and finish boards. Finish boards are requiring short-length clear lumber. commonly used for shelving and built-in cabi- network. Lumber for Remanufacture Most appearance lumber grades are de- scribed by letters and combinations of letters A wide variety of species, grades, and sizes (B&BTR, C&BTR, D). (See Standard Lumber of softwood lumber is supplied to industrial Abbreviations at the end of this chapter for accounts for cutting to specific smaller sizes 5-10 which become integral parts of other products. tics are important. The principal grades are In this secondary manufacturing process, grade B&BTR, C, and D. Grading is based primarily descriptions, sizes, and often the entire ap- on the best face, although the influence of edge pearance of the wood piece are changed. Thus characteristics is important and varies depend- the role of the grading process for these re- ing upon piece width and thickness. In red- manufacture items is to describe as accurately wood this grade may include an "all heart" as possible the yield to be obtained in the sub- requirement for decay resistance in manufac- sequent cutting operation. Typical of lumber ture of cooling towers, tanks, pipe, and simi- for secondary manufacture are the factory lar products. grades, industrial clears, box lumber, mold- ing stock, and ladder stock. The variety of spe- Molding, ladder, pole, tank, and pencil stock cies available for these purposes has led to a variety of grade names and grade definitions. Within producing regions, grading rules de- The following section briefly outlines some of lineate the requirements for a variety of lum- the more common classifications. For details, ber items oriented to specific consumer prod- reference must be made to industry sources. ucts. Custom and the characteristics of the Availability and grade designation often vary wood supply lead to different grade descrip- by region and species. tions and terminology. For example, in West Coast species, the ladder industry can choose Factory (Shop) grades. from one "ladder and pole stock" grade plus two ladder rail grades and one ladder rail Traditionally softwood lumber used for cut- stock grade. In southern pine, ladder stock is tings has been termed Factory or Shop. This available as Select and Industrial. Molding lumber forms the basic raw material for many stock, tank stock, pole stock, stave stock, sta- secondary manufacturing operations. Some dium seat stock, box lumber, and pencil stock grading associations refer to cutting grades as are other typical industrial grades oriented to Factory while others refer to Shop. All impose the final product. Some have only one grade a somewhat similar nomenclature in the grade level; a few offer two or three levels. Special structure. Factory Select and Select Shop are features of these grades may include a restric- typical high grades, followed by No. 1, No. 2, tion on sapwood related to desired decay resist- and No. 3 Shop. Door cuttings and sash cut- ance, specific requirements for slope of grain tings are specialized grade categories under and growth ring orientation for high-stress use which grade levels of No. 1, No. 2, and No. 3 such as ladders, and particular cutting require- Cuttings and No. 1, No. 2, and No. 3 Shop ments as in pencil stock. All references to these are applied. grades should be made directly to current lum- Grade characteristics of cuttings are in- ber association grading rules. fluenced by the width, length, and thickness of the basic piece and are based on the amount Structural laminations of high-quality material that can be removed by cutting. Typically, a Select Shop would be Structural laminating grades describe the required to contain either (a) 70 percent of characteristics used to segregate lumber for cuttings of specified size, clear on both sides structural glued-laminated timbers. Three typi- or (b) 70 percent cuttings of different size cal basic categories, LI, L2, and L3, exist with equal to a B&BTR Finish grade on one side. additional provisions for "Dense.*' The grade No. 1 Shop would be required to have 50 per- characteristics permitted are based on anti- cent of (a) or (b) ; No. 2 Shop would be re- cipated performance as a portion of the lam- quired to have 331/3 percent. Because of differ- inated product; however, allowable properties ent characteristics assigned to grades with are not assigned separately to the laminating similar nomenclature, grades labeled Factory or grades. Shop must be referenced to the appropriate in- dustry source. Softwood Lumber Manufacture

Industrial clears Size These grades are used for cabinet stock, Lumber length is recorded in actual dimen- door stock, and other product components sions while width and thickness are tradition- where excellent appearance, mechanical and ally recorded in ''nominal" dimensions—the physical properties, and finishing characteris- actual dimension being somewhat less.

5-11 Softwood lumber is manufactured in length faced green or dry at the prerogative of the multiples of 1 foot as specified in various manufacturer; therefore, both green and dry grading rules. In practice, 2-foot multiples (in standard sizes are given. The sizes are such even numbers) are the rule for most construc- that a piece of green lumber, surfaced to the tion lumber. Width of softwood lumber varies, standard green size, will shrink to approxi- commonly from 2 to 16 inch nominal. The mately the standard dry size as it dries down thickness of lumber can be generally catego- to about 15 percent moisture content. The rized as follows: American Lumber Standard definition of dry Boards,—lumber less than 2 inches in is a moisture content of 19 percent or less. nominal thickness. Many types of lumber are dried before surfac- Dimension.—lumber from 2 inches to, but ing and only dry sizes for these products are not including, 5 inches in nominal thick- given in the standard. ness. Lumber for remanufacture is offered in Timbers,—lumber 5 or more inches in specified sizes to fit end product requirements. nominal thickness in the least di- Factory grades for general cuttings (Shop) mension. are offered in thicknesses from less than 1 inch To standardize and clarify nominal-actual to over 3 inches depending on species. Thick- sizes the American Lumber Standard specifies nesses of door and sash cuttings start at 1% thickness and width for lumber that falls un- inches. Cuttings are various lengths and widths. der the standard. Laminating stock sometimes is offered over- The standard sizes for stress-graded and size, compared to standard dimension sizes, to nonstress-graded construction lumber are permit resurfacing prior to laminating. Indus- given in table 5-5. Timbers are usually sur- trial Clears can be offered rough or surfaced faced while green and only green sizes are in a variety of sizes starting from less than 2 given. Dimension and boards may be sur- inches thick and as narrow as 3 inches. Sizes Table 5-5.—American Standard lumber sizes for stress-graded and non- stress-graded lumber for construction ^

Item Thickness Face width Nominal Minimum dressed Nominal Minimum dressed Dry Green Dry Green In. In. In. In. In. In. Boards 1 % 2%2 2 11/2 1%6 1% 1 11/32 3 21/2 2%6 11/2 11/4 1%2 4 31/2 3%6 5 41/2 4% 6 5V2 5% 7 6I/2 6% 8 71/4 9 8I/4 8y2 10 9% 9V2 11 101/4 10 Vs 12 111/4 11 ¥2 14 131/4 13% 16 151/4 15%

Dimension 2 11/2 1%6 2 11/2 1%6 21/2 2 2I/16 3 21/2 2%6 3 21/2 2%6 4 31/2 3%6 31/2 3 3I/16 5 41/2 4% 4 31/2 3%6 6 51/2 5% 41/2 4 4^16 8 71/4 7% 10 91/4 91/2 12 111/4 11% 14 131/4 13 y2 16 151/4 15% Timbers 5 and V2 less 5 and % less greater than greater than nominal nominal ' Nominal sizes in the table are used for convenience. No inference should be drawn that they represent actual sizes.

5-12 for special product grades such as molding stock and ladder stock are specified in appro- priate grading rules or handled by purchase agreements. Surfacing