STORAGE of LUMBER by Raymond C
Total Page：16
File Type：pdf, Size：1020Kb
STORAGE OF LUMBER By Raymond C. Rietz Formerly Research Engineer Forest Products Laboratory Forest Service U.S. Department of Agriculture (Maintained at Madison, Wisconsin, in cooperation with the University of Wisconsin. ) AGRICULTURE HANDBOOK NO. 531 September 1978 Library of Congress Catalog Card No. 78-600012 Rietz, Raymond C. 1978. Storage of lumber. U.S. Dep. Agric., Agric. Handb. 531 63 p. Surveys the most effective current techniques for protecting the quality of stored lumber. Physical properties of wood which are basic to the storing of lumber in commerce are explained. Causes of storage losses in lumber are discussed. Individual chapters deal with protection of wood in specific storage environments, such as in yards, at manufacturing plants, or in transit. KEYWORDS: Degrade, drying, lumber, storage, wood properties The Forest Products Laboratory is maintained by the Forest Service, U.S. Department of Agricul- ture, at Madison, Wis., in cooperation with the University of Wisconsin. Mention of chemical treatment in this hand- book does not constitute a specific recommenda- tion; only those chemicals registered by the U.S. Environmental Protection Agency may be rec- ommended, and then only for uses as prescribed in the registration—and in the manner and at the concentration prescribed. The list of regis- tered chemicals varies from time to time; pros- pective users, therefore, should get current information on registration status from the Environmental Protection Agency, Washington, D.C. 20460. Page Page Illustration Requests Requests for copies of illustrations contained in this Handbook should be directed to the Forest Products Laboratory, U.S. Forest Service, P.O. Box 5130, Madison, Wis. 53705. PREFACE “How can I cut down grade loss in my stored with little waste if techniques are applied based lumber?” Forest Service specialists in wood on a scientific knowledge of wood properties. drying receive similar questions by phone or Chapters 1 through 4 of this handbook explain mail in research centers across the Nation. But physical properties of wood which are basic to such questions cannot be answered without more storing lumber commercially. The first four information. Are we talking about green or chapters will help answer such questions as dried lumber ? Air dried or kiln dried ? What these: Why does wood gain or lose moisture? species ? How long will the storage period be? What conditions must be met to keep kiln-dried What is the intended end use of the lumber? lumber dry ? What causes staining, decay, or What climate prevails in the storage region? warp ? How do hardwoods and softwoods differ Questions of lumber storage can lead into the in their storage properties? larger subject of lumber processing, and are often The remaining chapters of this handbook deal too complex to permit simple answers. Yet such with specific storage situations. Through text questions are of crucial importance because and photographs, they give practical details of degrade and decay during storage are a major the better handling, packaging, and storage cause of lumber losses. Such lumber waste procedures used in the lumber industry today. becomes intolerable as demands increase upon Specific problems are discussed, such as the our Nation’s limited supplies of sawtimber. The merits and limitations of package wrapping, the issue demands a comprehensive, practical publi- protection of lumber when in transit, and ways cation, and thus researchers from the Forest of protecting lumber from rain soaking at Service, U.S. Department of Agriculture, have construction sites. compiled this handbook. It should help to fulfill This book also gives recommendations for the Forest Service’s objective of conserving, and better storage at the end of several chapters, thereby extending, our Nation’s forest resources. suggestions for additional reading, and a Studies have shown that lumber can be stored glossary of terms. CHAPTER 1: PROTECTING LUMBER IN STORAGE A flatcar piled high with packages of lumber should be the major concern of the processor, moves across the Midwest, each package pro- agent, and user. tected in its own jacket of wrapping. Millwork awaits use at a construction site, covered by a tarpaulin and resting on small timbers to pre- Green and Partially Dried Lumber vent ground contact. Workmen dip packages of Green or partially dried lumber usually under- green lumber into a fungicide solution prior to goes controlled drying when in storage, and is shipment. These are examples of effective storage usually stickered and given some protection from and handling in today’s lumber industry, weather (fig.1 ). Green lumber bulk-piled for When is lumber said to be in storage? Between extended storage during warm weather is in cutting and use, lumber undergoes a complex danger from decay, stain, and insect attack. For series of stages in processing and transport. this reason, green lumber should be stickered During this time, lumber is frequently stored. for drying as soon as possible after sawn. When After drying and planing, softwood lumber may such lumber must remain bulk-piled in warm be stored before shipping, and then stored again weather, such as when shipped in the green in trucks, railroad cars, or a ship’s hold as it state, it is often protected by chemical treatment moves toward a destination. Hardwood lumber (chapter 5). is usually dried at the producing sawmill and moves as rough lumber to the using factories. Finally, lumber may be stored at wholesale and Dry, High-Grade Lumber retail distribution yards, at woodworking plants, and at the construction site. At times the maximum moisture content The moisture content of lumber must be acceptable for construction lumber is set by controlled in storage. Moisture changes in lum- industry practice, and at other times by standards ber may at times be the direct cause of grade and codes. Certain industry grading rules, for loss. For example, the best lumber will be un- example, require that softwood dimension lumber suitable for many uses if its moisture content used in the framing of houses be below 19 percent goes too high. Also, moisture changes in lumber moisture content. Lumber for use in the heated may be an indirect cause of deterioration. For interiors of buildings should properly be still example, rapid and uneven moisture changes drier; its moisture content should not exceed 8 can cause checking and warpage. Also, lumber percent, with a moisture content of over 20 percent may Therefore, those who handle dried high-grade develop stain or decay. (The figure of 20 percent lumber must be careful that it not take on includes a safety factor; lumber’s moisture con- excessive moisture in storage or transport. For tent is measured as a percentage by weight of example, finished lumber at a construction site the Completely dried wood substance. ) Most should not be allowed to undergo soaking from insect damage to lumber can be avoided if it is rain because this would jeopardize its structural well dried. performance. Controlling moisture content in stored lumber, The problem is especially acute with kiln-dried as it moves from sawmill to its final destination, lumber to be used in an interior location. If such lumber becomes wet enough to require redrying, additional labor and expense are required. Also, the lumber will again undergo some degrade from the drying process and refinishing may be required. Dry, high-grade lumber is best protected from moisture regain when stored as solid packages under roof (fig. 2). Closed storage sheds offer the best protection from moisture regain during long-term storage (fig. 3). Lumber During Transport and Handling Lumber handling has become mechanized to reduce overall costs at sawmills, distribution yards, factories, and construction sites. Trans- port methods have changed to speed up the loading and unloading of trucks, boxcars (fig. 4), flatcars, and ocean-going vessels. The merits Unprotected Lumber Outdoors of mechanized handling will diminish if lumber’s moisture content increases during this handling. High-quality lumber will endure for a short time storage conditions which, if sustained, High-quality lumber can be protected in would cause grade and footage losses. HOW several ways during transport. Tight boxcars tolerant any given lot of lumber may be to lack and dry ship holds can minimize moisture regain. of protection, such as when transported on open Packages of lumber exposed during transport, trucks, depends upon the time exposed, the such as on open flatcars or tractor-trailer trucks, weather, and qualities of the lumber itself. can be temporarily protected by sheet wrapping Generally, thicker pieces of wood, such as dimen- (fig. 5). Sheet wraps can also protect lumber at sion lumber, will regain moisture more slowly unloading points or during temporary storage at than thinner pieces, such as nominal l-inch distribution yards (fig. 6). boards. Hardwoods are more resistant to mois- 3 ture regain than softwoods, dense woods more High relative humidity alone will not elevate resistant than less dense, and heartwood more moisture levels of dried lumber sufficiently to resistant than sapwood. cause serious decay, but may permit some mold to develop. High humidity may also raise the Benefits of Protective Storage moisture content of kiln-dried lumber enough so that the lumber must be redried to be used in an Control of atmospheric conditions during interior service location. lumber storage, principally relative humidity, Bulk-piled lumber in bins or unit packages can create a moisture balance in the lumber absorbs moisture at all exposed faces of the pile. suited to its end use. Thus the lumber’s com- This moisture moves toward the pile interior. mercial quality can actually be improved by Movement is more rapid along the grain, and storage. the penetration of moisture absorbed at the open Dry lumber is usually bulk-piled when stored cell ends will be the greatest.