ISSUE 1/2005 „ VOLUME 22 „ NUMBER 1

Journal of architectural technology published by Hoffmann Architects, Inc., specialists in the rehabilitation of building exteriors. Repair and Maintenance of Historic Marble and Limestone Structures Regular Maintenance Key to Longevity

Arthur L. Sanders, AIA and Lawrence E. Keenan, AIA, PE

W hether you’re thumbing One of the more enduring building through the pages of a history book materials, stone has been used or surfing the web, it’s easy to see throughout history for building that stone is a lasting testament to construction. In particular, marble and architecture through the ages. limestone are two of the most commonly encountered materials in historic structures. For thousands of years, these materials have been valued for their beauty and versatility.

Despite their aura of permanence, both limestone and marble can suffer from time and wear. As a result of today’s increasing urbanization and pollution, stone deterioration is occurring far more rapidly than in the past. Dirt accumulation, cracked masonry, spalling and loss of structural integrity are among the problems affecting stone structures.

Origin of Limestone and Marble

Limestone is a broad term that refers to many types of sedimentary rock in which calcium carbonate is the major

> Inappropriately applied sealant is failing, or missing altogether, in joints. Areas of the sculpture are constituent. One hundred million to beginning to show signs of erosion. 500 million years old, limestone is derived from fossil deposits of marine animals. It generally has a uniform

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Arthur L. Sanders, AIA is Senior Vice President and Director, Architecture and Lawrence E. Keenan, AIA, PE is Director, Engineering with Hoffmann Architects, Inc. They are specifically experienced in the rehabilitation of marble and limestone structures. JOURNAL

(continued from page 1) consistency and texture and is usually construction techniques are examples barrier wall systems must be sealed. buff or off-white in color, but it can of craftsmanship that characterize a Repairs for each can be drastically also be gray or very light in tone. property and should be maintained. different. The interaction of building Marble is primarily a metamorphic If possible, deteriorated historic components (roof, parapets, form of limestone, transformed under features should be repaired. If windows, doors, etc.) must also be intense heat and pressure into a replacement is necessary, the new understood. hardened mass of calcium carbonate. feature should match the old as much In general, marble has a much finer as possible in design, color, texture What Is the Condition texture than limestone, which allows it and other visual qualities. Of YYYour Building? to be polished. Limestone cannot be polished. Where to Start?t?t? A thorough assessment of your building’s exterior condition is the next ImporImporImportance of Repairinginging The first step in the rehabilitation of step in the development of the scope Historic Marble and Limestone stone at a building’s exterior involves of required work for a successful the accurate assessment of that stone rehabilitation program. A building’s exterior provides building’s existing system. In other Identification of problem conditions protection from the elements and words, before you can know how to early in the process is less costly by conveys its historic character. The fix something, you have to know how far than “righting” wrongs after your age, style and significance of a building it was intended to work in the first project has been completed. That or structure can often be understood place. Then a proper scope of condition assessment should include: by analyzing exterior designs, features rehabilitative work can be established. and materials. Changes in taste, 1. Identification and/or classification fashion, architectural style and use may As water is the primary cause of of existing materials; be evident. In any rehabilitation deterioration, understanding the project, it is critical to treat the management of water in the façade is 2. Evaluation of existing façade exterior with great care. absolutely essential. Mass wall systems including drainage, insulation, systems must be allowed to breathe, vapor barriers and structural Distinctive features, finishes and cavity wall systems must drain, and supports;

(continued on page 3) > > Large spall is shown in limestone panel above window Removal of spall exposes corroded steel beam behind stone panel.

2 VOLUME 22 „ NUMBER 1

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3. Thorough inspection of all elements documenting all signs of deterioration and defects;

4. Investigation of hidden conditions through probes into exterior building components;

5. Investigation of material deterioration through field and laboratory testing methods; and

6. Identification of potentially hazardous and/or unsafe conditions.

The subsequent development of a realistic budget and project schedule, and the preparation of appropriate design documentation, materials and

systems specifications, will ensure that > A worker scrubs and removes softened soil from the water-soaked limestone façade. a good stone rehabilitation program can be executed.

In For a PPIn ennennennyyy,,, In For a Poundoundound Removing a large piece of stone on the rusted steel embedded in the Proper repair of stone façade the side of a façade any number of wall), the crack and adjacent joints are elements can seem costly. However, stories above the ground may seem sealed with patching mortar or this cost can easily be eclipsed by the daunting, but this might be the only caulking compound, water would still cost of correcting deferred repairs or way to access the defective condition. continue to enter the stone. The ignored defects. Repairs that only Specially trained design professionals embedded steel would continue to address problems on the surface can and contractors are necessary to rust and expand, displacing the mask deeper issues and often allow undertake such work. patched stone once again. deterioration to continue unnoticed. In the long run, cost-effective repairs Consider, for example, that a property Sources of Deterioration In Stone always correct the root problem first manager discovers a crack at the before restoring the damaged finish base of a stone panel on a building There are many sources of stone material. façade (see photos on page 2). deterioration. Damage occurs through weathering, the invasive It would be difficult to justify repairing Proper repair of the condition should action of plant growth, pollution, and a water-damaged ceiling below a start with removing enough of the dirt accumulation. Further damage leaking roof without first repairing the stone to identify the root cause. can occur through erosion, as a result leaky roof. However, this type of Repairs could consist of removing all of movement in stone (thermal repair happens with façades more the spalled stone, preparing and expansion/contraction), faulty or often that you’d think. It’s important painting the embedded steel and then broken anchors, and even human to understand the nature of the repairing the stone with either a error in design, engineering or problem and the methods necessary dutchman or patching mortar to construction. to repair the defect. Be wary of match the existing stone. If, however, solutions that don’t completely prior to identification of the root Because marble and limestone are address the problem. cause of the stone spall (in this case, carbonates, both stones present

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3 JOURNAL > > Figure 1 Figure 2 > Figure 3

(continued from page 3) several key maintenance and common defects and possible causes migration of damaging moisture from preservation problems, for example: of damage. The underlying causes, as within the wall system. (Figure 1) well as the indicators themselves, 1. Unlike granite, marble and should be thoroughly investigated Re-anchorRe-anchorRe-anchoringinging is usually necessary limestone are highly sensitive to and before any rehabilitative work is when movement of the stone from its soluble in acid (think baking soda and performed. There is no value, for original position has broken existing vinegar). The natural acidity of rainfall example, in patching a cracked marble anchors or fractured the back of the – even without the compounded wall panel if the cause for the crack stone. (Figure 2) effects of acid rain, automobile lies behind the panel at its anchorage exhaust and other airborne pollutants system. PinningPinningPinning stonework is performed by – will cause the stones to deteriorate securing non-corrosive rods through over time. Common Repair TTTechniquesechniquesechniques the stone into the masonry backing. (Figure 3) 2. Marble and limestone are porous Cracked, spalled or exfoliated and absorb water readily. The rate limestone and marble should be PatchingPatchingPatching is used to repair small areas of absorption and the level of repaired in a timely manner to of damaged stone with a matching porosity vary. Water trapped within prevent further damage. Typical cementitious material that is applied the stone will exacerbate repair methods include the following: and built up in layers until it matches deterioration. Therefore, it is the original profile. For larger patches, important to ensure that moisture RepointingRepointingRepointing requires cutting out failed pins might be needed to secure the infiltrating the stone can evaporate. joint mortar and applying new mortar new material. that is finished to replicate the original 3. Marble and limestone are mortar style. There are two SculptingSculptingSculpting is the process of re-carving relatively soft stones and can be important points to take into badly eroded stone or re-accentuating easily scratched and marred. This consideration when repointing: the indistinct detailing. This method is softness means chemical cleaners, new mortar should be of a weaker frequently employed to repair sandblasting and wind-driven grit will compressive strength than the ornamentation. take their destructive toll. surrounding masonry to avoid spalls at the joints, and joint sealant is not ResettingResettingResetting returns displaced stone to The chart on page 6 shows some recommended, as it prevents the its original position.

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Stone replacement can be the most viable approach for restoring large areas of damage. A new anchoring system may be required.

Crack repair can be accomplished by injecting an adhesive material into the fissure to provide water impermeability and prevent further cracking. A minor crack can be successfully repaired by routing the crack and filling it with patching material.

Consolidation is a time-tested technique of reconstituting softened or deteriorated stone by filling the voids and binding the grains within the stone. Consolidation has many applications for the preservation of historic structures, but requires thorough testing and evaluation to > Figure 4a ensure that the consolidant leaves a compatible vapor-permeable surface. (Figures 4a and 4b)

A A WWWord AboutAboutAbout “Protective” Coatings

Waterproof coatings should rarely, if ever, be used on stone. Although these coatings prevent water infiltration, they have a tendency to trap moisture within the stone and the masonry in general. Even water- repellent sealers will prevent the natural migration of water from stone and should be used with great caution, if at all.

Ongoing Maintenance And Cleaning

Ongoing maintenance is essential to > Figure 4b preserve exterior stone surfaces and to prevent future deterioration. A good maintenance program includes > Erosion of volute face of marble column capital exposed to weather (Figure 4a). The illustration routine inspections to detect early demonstrates consolidation methods used to repair the damaged area (Figure 4b).

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Common Marble and Limestone Problems ConditionsConditionsConditions DescriptionDescriptionDescription Probable Causes

Open JointsJointsOpen Loose, broken mortar Result of poor mortar bond, building movement, aging and water intrusion.

CrCrCrumbumbumbling or Sugaringinging Brittle or broken stone; Typically caused by the binder loose granules material being dissolved or weakened through the intrusion of water.

Gypsum Encrustationustationustation Hard, gray surficial deposits Reaction of sulphates in pollution with carbonates in stone. Creates impermeable surface.

Efflorescence Hazy, white blotching or crystalline Naturally occurring salts within deposits on stone surface mortar and masonry materials that are dissolved and deposited on the surface.

ErosionErosionErosion Worn edges or surfaces Natural wearing away of the stone through weathering and chemical degradation.

CrackingCrackingCracking Narrow, irregular fissures in Movement within the façade from stone surface expansion, contraction, settlement or other issues. Longer or wider cracks may be evidence of structural flaws.

SpallingSpallingSpalling Fracture and loss of surface Caused by trapped moisture or lamination crystallized salts, corrosion of embedded steel or iron, freeze-thaw cycles or joint mortars that do not allow for natural expansion and contraction.

Grime, Organic Growth, Dark patches, stains, discoloration Accumulation of waterborne and Black CrCrBlack usustustt airborne dirt and pollutants or lichen and algae. Some lichen secrete organic acids that eat away at the stone.

StrStrStructuructuructural System Flawswsws Surface evidence of these hidden Causes include improper design or problems may include cracking installation, inappropriate mortars and displaced stone pieces and insufficient or incorrect anchoring systems.

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Marble and Limestone Rehabilitation HarHarHartftftford InsurInsurord ance Headquartertertersss Hartford, Connecticut These representative projects included Limestone Façade Restoration marble and limestone rehabilitation.

O ne One WWWall StreetStreetall Columbia Univererersity Butler Librarararyyy New York, New York New York, New York Limestone Façade Rehabilitation Limestone Façade Renovation

U.S. Bureau of Engraving and Printing Church of Scientology Washington, D.C. New York, New York Limestone Façade Restoration Limestone Façade Rehabilitation

New HaHaNew vvven CourCouren thousethousethouse Cannon House Office Building New Haven, Connecticut Washington, D.C. Marble Repair and Renovations Marble Ballustrade/Stair Rehabilitation > New YYYororork Stock Exchange New York, New Yo r k TTTaft AparAparApartmentstmentstments FolgerFolgerFolger-Shak-Shak-Shakespeare LibrLibrespeare arararyyy New Haven, Connecticut Washington, D.C. Limestone Façade Rehabilitation Marble Rehabilitation

N ew New YYYororork Stock Exchange Johns Hopkins Univererersity NatatorNatatorsity iumiumium New York, New York Baltimore, Maryland Marble Façade Restoration Limestone Rehabilitation

Hoffmann-La Roche, Building 76 Radio City Music Hall

Nutley, New Jersey New York, New York > U.S. Bureau of Engraving and Printing Marble Panel Rehabilitation Limestone Façade Rehabilitation Washington, D.C.

VVVerererizizizon Headquartertertersss CarCarCarnegie Mellon Univererersitysitysity 1095 1095 AAAvvvenenenue of the AmerAmerAmericasicasicas Mellon Institute New York, New York Pittsburgh, Pennsylvania Marble Panel Rehabilitation Limestone Façade Study

310 Orange Street PrPrPrinceton Univererersity Mather Sundial

New Haven, Connecticut Princeton, New Jersey > Hartftftford InsurInsurord ance Headquartertertersss Limestone Façade Rehabilitation Limestone Survey Hartford, Connecticut

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(continued from page 5) signs of stone damage and joint Who Is Qualified TTTo Do the WWWororork?k?k? failure. JOURNAL is a publication of Hoffmann Architects, Inc., specialists in the rehabilita- Walk down any street, in any city, and tion of building exteriors. The firm’s work Regular washing keeps dirt and you’ll more than likely see good stone includes investigative and rehabilitative pollutants from accumulating on stone, rehabilitation intentions gone bad … architecture and engineering services for helping prevent deterioration. You stone “rehabilitation” work that has the analysis and resolution of problems should correctly identify stone before caused more harm than good. At within roofs, façades, glazing, and cleaning, because certain cleaning the Acropolis in Athens, Greece, for structural systems of existing buildings, plazas, terraces and parking garages. agents and treatments, if improperly example, a botched 1930s marble applied, may cause or accelerate restoration project involved the use of Please send news, technical information, physical deterioration in stone. For iron clamps that rusted over time, address changes or requests for free that reason, it’s best to use the causing the structures to further crack subscriptions to Editor, Hoffmann mildest cleaning method possible to and crumble. The outcome was Architects JOURNAL, 432 Washington get the job done. unfortunate and avoidable. Avenue, North Haven, CT 06473. For information on the services offered Because marble and limestone are When it comes to stone rehabilitation, by Hoffmann Architects, Inc., contact especially sensitive to acid-based you can count on one thing. What Sandra Matheny, Senior Vice President, cleaners, water washing is usually the you don’t know will hurt you. It’s at 800-239-6665. best treatment. Washing by bucket essential to work with design and brush is a well-established professionals and restoration 432 Washington Avenue method of cleaning marble and contractors who are knowledgeable, North Haven, CT 06473 limestone surfaces. Spraying and trained and experienced in restoring 203-239-6660 misting (soaking) is effective on stone structures and surfaces. marble and limestone for removing 500 Fifth Avenue, Suite 830 New York, NY 10110 heavy accumulations of soot or crusts ConclusionConclusionConclusion 212-789-9915 that have a tendency to form in protected areas that are not regularly Although deterioration in limestone and 1001 Connecticut Avenue NW, Suite 825 washed by rain. marble is inevitable, there are ways to Washington, DC 20036 slow the process and prevent serious 202-530-1100 A purification system might be damage. Routine maintenance and For more information on the topics needed to eliminate the corrosive inspections can reveal surface damage, discussed in this article, visit us on the effects of impurities in the water. displacement and joint failure that can web at www.hoffarch.com or contact And it goes without saying: the signify more serious underlying us at [email protected] surface you’re cleaning should be conditions. Early detection and Editor: Ruthanne Bell watertight. prompt, careful attention are key.

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