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. Arthur L. Sanders, AIA and Lawrence E. Keenan, AIA, PE Journal of architectural technology published by Hoffmann Architects, Inc., specialists in the rehabilitation of building exteriors. ISSUE 1/ 2 0 0 5 VOLUME 22 NUMBER 1 W (continued on page 2) Repair and Maintenance of Historic Marble and Limestone Structures hether you’re thumbing through the pages of a history book or surfing the web, it’s easy to see that stone is a lasting testament to architecture through the ages. One of the more enduring building materials, stone has been used throughout history for building construction. In particular, marble and 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 Origin of Limestone and Marble Origin of Limestone and Marble Origin of Limestone and Marble 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 constituent. One hundred million to 500 million years old, limestone is derived from fossil deposits of marine animals. It generally has a uniform Regular Maintenance Key to Longevity Inappropriately applied sealant is failing, or missing altogether, in joints. Areas of the sculpture are beginning to show signs of erosion. >
Transcript
Arthur L. Sanders, AIA is Senior Vice President and Director, Architecture and Lawrence E. Keenan, AIA, PEis Director, Engineering with Hoffmann Architects, Inc. They are specifically experienced in therehabilitation of marble and limestone structures.
Arthur L. Sanders, AIA and Lawrence E. Keenan, AIA, PE
Journal of architectural
technology published
by Hoffmann Architects, Inc.,
specialists in the rehabilitation
of building exteriors.
I S S U E 1 / 2 0 0 5 V O L U M E 22 N U M B E R 1
W
(continued on page 2)
Repair and Maintenance of HistoricMarble and Limestone Structures
hether you’re thumbingthrough the pages of a history bookor surfing the web, it’s easy to seethat stone is a lasting testament toarchitecture through the ages.
One of the more enduring buildingmaterials, stone has been usedthroughout history for buildingconstruction. In particular, marble andlimestone are two of the mostcommonly encountered materials inhistoric structures. For thousands ofyears, these materials have beenvalued for their beauty and versatility.
Despite their aura of permanence,both limestone and marble can sufferfrom time and wear. As a result oftoday’s increasing urbanization andpollution, stone deterioration isoccurring far more rapidly than in thepast. Dirt accumulation, crackedmasonry, spalling and loss ofstructural integrity are among theproblems affecting stone structures.
Origin of Limestone and MarbleOrigin of Limestone and MarbleOrigin of Limestone and MarbleOrigin of Limestone and MarbleOrigin of Limestone and Marble
Limestone is a broad term that refersto many types of sedimentary rock inwhich calcium carbonate is the majorconstituent. One hundred million to500 million years old, limestone isderived from fossil deposits of marineanimals. It generally has a uniform
Regular Maintenance Key to Longevity
Inappropriately applied sealant is failing, or missing altogether, in joints. Areas of the sculpture are
beginning to show signs of erosion.
>
Removal of spall exposes corroded steel beam behind stone panel.
construction techniques are examplesof craftsmanship that characterize aproperty and should be maintained.If possible, deteriorated historicfeatures should be repaired. Ifreplacement is necessary, the newfeature should match the old as muchas possible in design, color, textureand other visual qualities.
Where to StarWhere to StarWhere to StarWhere to StarWhere to Start?t?t?t?t?
The first step in the rehabilitation ofstone at a building’s exterior involvesthe accurate assessment of thatbuilding’s existing system. In otherwords, before you can know how tofix something, you have to know howit was intended to work in the firstplace. Then a proper scope ofrehabilitative work can be established.
As water is the primary cause ofdeterioration, understanding themanagement of water in the façade isabsolutely essential. Mass wallsystems must be allowed to breathe,cavity wall systems must drain, and
barrier wall systems must be sealed.Repairs for each can be drasticallydifferent. The interaction of buildingcomponents (roof, parapets,windows, doors, etc.) must also beunderstood.
What Is the ConditionWhat Is the ConditionWhat Is the ConditionWhat Is the ConditionWhat Is the ConditionOf Of Of Of Of YYYYYour Building?our Building?our Building?our Building?our Building?
A thorough assessment of yourbuilding’s exterior condition is the nextstep in the development of the scopeof required work for a successfulstone rehabilitation program.Identification of problem conditionsearly in the process is less costly byfar than “righting” wrongs after yourproject has been completed. Thatcondition assessment should include:
2. Evaluation of existing façadesystems including drainage, insulation,vapor barriers and structuralsupports;
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J O U R N A L
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consistency and texture and is usuallybuff or off-white in color, but it canalso be gray or very light in tone.Marble is primarily a metamorphicform of limestone, transformed underintense heat and pressure into ahardened mass of calcium carbonate.In general, marble has a much finertexture than limestone, which allows itto be polished. Limestone cannot bepolished.
ImporImporImporImporImportance of Repairtance of Repairtance of Repairtance of Repairtance of RepairingingingingingHistoric Marble and LimestoneHistoric Marble and LimestoneHistoric Marble and LimestoneHistoric Marble and LimestoneHistoric Marble and Limestone
A building’s exterior providesprotection from the elements andconveys its historic character. Theage, style and significance of a buildingor structure can often be understoodby analyzing exterior designs, featuresand materials. Changes in taste,fashion, architectural style and use maybe evident. In any rehabilitationproject, it is critical to treat theexterior with great care.
Distinctive features, finishes and
Large spall is shown in limestone panel above window >>
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V O L U M E 22 N U M B E R 1
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3. Thorough inspection of allelements documenting all signs ofdeterioration and defects;
4. Investigation of hidden conditionsthrough probes into exterior buildingcomponents;
5. Investigation of materialdeterioration through field andlaboratory testing methods; and
6. Identification of potentiallyhazardous and/or unsafe conditions.
The subsequent development of arealistic budget and project schedule,and the preparation of appropriatedesign documentation, materials andsystems specifications, will ensure thata good stone rehabilitation programcan be executed.
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Proper repair of stone façadeelements can seem costly. However,this cost can easily be eclipsed by thecost of correcting deferred repairs orignored defects. Repairs that onlyaddress problems on the surface canmask deeper issues and often allowdeterioration to continue unnoticed.In the long run, cost-effective repairsalways correct the root problem firstbefore restoring the damaged finishmaterial.
It would be difficult to justify repairinga water-damaged ceiling below aleaking roof without first repairing theleaky roof. However, this type ofrepair happens with façades moreoften that you’d think. It’s importantto understand the nature of theproblem and the methods necessaryto repair the defect. Be wary ofsolutions that don’t completelyaddress the problem.
Removing a large piece of stone onthe side of a façade any number ofstories above the ground may seemdaunting, but this might be the onlyway to access the defective condition.Specially trained design professionalsand contractors are necessary toundertake such work.
Consider, for example, that a propertymanager discovers a crack at thebase of a stone panel on a buildingfaçade (see photos on page 2).
Proper repair of the condition shouldstart with removing enough of thestone to identify the root cause.Repairs could consist of removing allthe spalled stone, preparing andpainting the embedded steel and thenrepairing the stone with either adutchman or patching mortar tomatch the existing stone. If, however,prior to identification of the rootcause of the stone spall (in this case,
the rusted steel embedded in thewall), the crack and adjacent joints aresealed with patching mortar orcaulking compound, water would stillcontinue to enter the stone. Theembedded steel would continue torust and expand, displacing thepatched stone once again.
Sources of Deterioration In StoneSources of Deterioration In StoneSources of Deterioration In StoneSources of Deterioration In StoneSources of Deterioration In Stone
There are many sources of stonedeterioration. Damage occursthrough weathering, the invasiveaction of plant growth, pollution, anddirt accumulation. Further damagecan occur through erosion, as a resultof movement in stone (thermalexpansion/contraction), faulty orbroken anchors, and even humanerror in design, engineering orconstruction.
Because marble and limestone arecarbonates, both stones present
A worker scrubs and removes softened soil from the water-soaked limestone façade.>
common defects and possible causesof damage. The underlying causes, aswell as the indicators themselves,should be thoroughly investigatedbefore any rehabilitative work isperformed. There is no value, forexample, in patching a cracked marblewall panel if the cause for the cracklies behind the panel at its anchoragesystem.
Common Repair Common Repair Common Repair Common Repair Common Repair TTTTTechniquesechniquesechniquesechniquesechniques
Cracked, spalled or exfoliatedlimestone and marble should berepaired in a timely manner toprevent further damage. Typicalrepair methods include the following:
RepointingRepointingRepointingRepointingRepointing requires cutting out failedjoint mortar and applying new mortarthat is finished to replicate the originalmortar style. There are twoimportant points to take intoconsideration when repointing: thenew mortar should be of a weakercompressive strength than thesurrounding masonry to avoid spallsat the joints, and joint sealant is notrecommended, as it prevents the
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several key maintenance andpreservation problems, for example:
1. Unlike granite, marble andlimestone are highly sensitive to andsoluble in acid (think baking soda andvinegar). The natural acidity of rainfall– even without the compoundedeffects of acid rain, automobileexhaust and other airborne pollutants– will cause the stones to deteriorateover time.
2. Marble and limestone are porousand absorb water readily. The rateof absorption and the level ofporosity vary. Water trapped withinthe stone will exacerbatedeterioration. Therefore, it isimportant to ensure that moistureinfiltrating the stone can evaporate.
3. Marble and limestone arerelatively soft stones and can beeasily scratched and marred. Thissoftness means chemical cleaners,sandblasting and wind-driven grit willtake their destructive toll.
The chart on page 6 shows some
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migration of damaging moisture fromwithin the wall system. (Figure 1)
Re-anchorRe-anchorRe-anchorRe-anchorRe-anchoringinginginging is usually necessarywhen movement of the stone from itsoriginal position has broken existinganchors or fractured the back of thestone. (Figure 2)
PinningPinningPinningPinningPinning stonework is performed bysecuring non-corrosive rods throughthe stone into the masonry backing.(Figure 3)
PatchingPatchingPatchingPatchingPatching is used to repair small areasof damaged stone with a matchingcementitious material that is appliedand built up in layers until it matchesthe original profile. For larger patches,pins might be needed to secure thenew material.
SculptingSculptingSculptingSculptingSculpting is the process of re-carvingbadly eroded stone or re-accentuatingindistinct detailing. This method isfrequently employed to repairornamentation.
ResettingResettingResettingResettingResetting returns displaced stone toits original position.
Figure 1> Figure 2> Figure 3>
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Stone replacementStone replacementStone replacementStone replacementStone replacement can be the mostviable approach for restoring largeareas of damage. A new anchoringsystem may be required.
Crack repairCrack repairCrack repairCrack repairCrack repair can be accomplishedby injecting an adhesive materialinto the fissure to provide waterimpermeability and prevent furthercracking. A minor crack can besuccessfully repaired by routing thecrack and filling it with patchingmaterial.
ConsolidationConsolidationConsolidationConsolidationConsolidation is a time-testedtechnique of reconstituting softenedor deteriorated stone by filling thevoids and binding the grains withinthe stone. Consolidation has manyapplications for the preservation ofhistoric structures, but requiresthorough testing and evaluation toensure that the consolidant leaves acompatible vapor-permeable surface.(Figures 4a and 4b)
A A A A A WWWWWord ord ord ord ord AboutAboutAboutAboutAbout“Protective” Coatings“Protective” Coatings“Protective” Coatings“Protective” Coatings“Protective” Coatings
Waterproof coatings should rarely, ifever, be used on stone. Althoughthese coatings prevent waterinfiltration, they have a tendency totrap moisture within the stone andthe masonry in general. Even water-repellent sealers will prevent thenatural migration of water from stoneand should be used with greatcaution, if at all.
Ongoing maintenance is essential topreserve exterior stone surfaces andto prevent future deterioration. Agood maintenance program includesroutine inspections to detect early
V O L U M E 22 N U M B E R 1
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Figure 4a>
Erosion of volute face of marble column capital exposed to weather (Figure 4a). The illustrationdemonstrates consolidation methods used to repair the damaged area (Figure 4b).
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Figure 4b>
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Common Marble and Limestone ProblemsCommon Marble and Limestone ProblemsCommon Marble and Limestone ProblemsCommon Marble and Limestone ProblemsCommon Marble and Limestone Problems
Open JointsOpen JointsOpen JointsOpen JointsOpen Joints Loose, broken mortar Result of poor mortar bond,building movement, aging and waterintrusion.
CrCrCrCrCrumbumbumbumbumbling or Sugarling or Sugarling or Sugarling or Sugarling or Sugaringinginginging Brittle or broken stone; Typically caused by the binderloose granules material being dissolved or
weakened through the intrusion ofwater.
Gypsum EncrGypsum EncrGypsum EncrGypsum EncrGypsum Encrustationustationustationustationustation Hard, gray surficial deposits Reaction of sulphates in pollutionwith carbonates in stone. Createsimpermeable surface.
EfflorescenceEfflorescenceEfflorescenceEfflorescenceEfflorescence Hazy, white blotching or crystalline Naturally occurring salts withindeposits on stone surface mortar and masonry materials that
are dissolved and deposited on thesurface.
ErosionErosionErosionErosionErosion Worn edges or surfaces Natural wearing away of the stonethrough weathering and chemicaldegradation.
CrackingCrackingCrackingCrackingCracking Narrow, irregular fissures in Movement within the façade fromstone surface expansion, contraction, settlement
or other issues. Longer or widercracks may be evidence ofstructural flaws.
SpallingSpallingSpallingSpallingSpalling Fracture and loss of surface Caused by trapped moisture orlamination crystallized salts, corrosion of
embedded steel or iron, freeze-thawcycles or joint mortars that do notallow for natural expansion andcontraction.
Grime, Organic Growth,Grime, Organic Growth,Grime, Organic Growth,Grime, Organic Growth,Grime, Organic Growth, Dark patches, stains, discoloration Accumulation of waterborne andBlack CrBlack CrBlack CrBlack CrBlack Crustustustustust airborne dirt and pollutants or
lichen and algae. Some lichensecrete organic acids that eat awayat the stone.
StrStrStrStrStructuructuructuructuructural System Flaal System Flaal System Flaal System Flaal System Flawswswswsws Surface evidence of these hidden Causes include improper design orproblems may include cracking installation, inappropriate mortarsand displaced stone pieces and insufficient or incorrect
anchoring systems.
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Marble and Limestone RehabilitationMarble and Limestone RehabilitationMarble and Limestone RehabilitationMarble and Limestone RehabilitationMarble and Limestone Rehabilitation
These representative projects includedmarble and limestone rehabilitation.
One One One One One WWWWWall Streetall Streetall Streetall Streetall StreetNew York, New YorkLimestone Façade Rehabilitation
U.S. Bureau of Engraving and PrintingU.S. Bureau of Engraving and PrintingU.S. Bureau of Engraving and PrintingU.S. Bureau of Engraving and PrintingU.S. Bureau of Engraving and PrintingWashington, D.C.Limestone Façade Restoration
New HaNew HaNew HaNew HaNew Havvvvven Couren Couren Couren Couren CourthousethousethousethousethouseNew Haven, ConnecticutMarble Repair and Renovations
New New New New New YYYYYororororork Stock Exchangek Stock Exchangek Stock Exchangek Stock Exchangek Stock ExchangeNew York, New YorkMarble Façade Restoration
Hoffmann-La Roche, Building 76Hoffmann-La Roche, Building 76Hoffmann-La Roche, Building 76Hoffmann-La Roche, Building 76Hoffmann-La Roche, Building 76Nutley, New JerseyMarble Panel Rehabilitation
VVVVVerererererizizizizizon Headquaron Headquaron Headquaron Headquaron Headquartertertertertersssss1095 1095 1095 1095 1095 AAAAAvvvvvenenenenenue of the ue of the ue of the ue of the ue of the AmerAmerAmerAmerAmericasicasicasicasicasNew York, New YorkMarble Panel Rehabilitation
Columbia UnivColumbia UnivColumbia UnivColumbia UnivColumbia Univererererersity Butler Librsity Butler Librsity Butler Librsity Butler Librsity Butler LibrarararararyyyyyNew York, New YorkLimestone Façade Renovation
Church of ScientologyChurch of ScientologyChurch of ScientologyChurch of ScientologyChurch of ScientologyNew York, New YorkLimestone Façade Rehabilitation
Cannon House Office BuildingCannon House Office BuildingCannon House Office BuildingCannon House Office BuildingCannon House Office BuildingWashington, D.C.Marble Ballustrade/Stair Rehabilitation
Radio City Music HallRadio City Music HallRadio City Music HallRadio City Music HallRadio City Music HallNew York, New YorkLimestone Façade Rehabilitation
New New New New New YYYYYororororork Stock Exchangek Stock Exchangek Stock Exchangek Stock Exchangek Stock ExchangeNew York, New York
V O L U M E 22 N U M B E R 1
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U.S. Bureau of Engraving and Printing U.S. Bureau of Engraving and Printing U.S. Bureau of Engraving and Printing U.S. Bureau of Engraving and Printing U.S. Bureau of Engraving and PrintingWashington, D.C.
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Har Har Har Har Hartftftftftford Insurord Insurord Insurord Insurord Insurance Headquarance Headquarance Headquarance Headquarance HeadquartertertertertersssssHartford, Connecticut
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432 Washington AvenueNorth Haven, Connecticut 06473
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JOURNAL is a publication of HoffmannArchitects, Inc., specialists in the rehabilita-tion of building exteriors. The firm’s workincludes investigative and rehabilitativearchitecture and engineering services forthe analysis and resolution of problemswithin roofs, façades, glazing, andstructural systems of existing buildings,plazas, terraces and parking garages.
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J O U R N A L
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signs of stone damage and jointfailure.
Regular washing keeps dirt andpollutants from accumulating on stone,helping prevent deterioration. Youshould correctly identify stone beforecleaning, because certain cleaningagents and treatments, if improperlyapplied, may cause or acceleratephysical deterioration in stone. Forthat reason, it’s best to use themildest cleaning method possible toget the job done.
Because marble and limestone areespecially sensitive to acid-basedcleaners, water washing is usually thebest treatment. Washing by bucketand brush is a well-establishedmethod of cleaning marble andlimestone surfaces. Spraying andmisting (soaking) is effective onmarble and limestone for removingheavy accumulations of soot or cruststhat have a tendency to form inprotected areas that are not regularlywashed by rain.
A purification system might beneeded to eliminate the corrosiveeffects of impurities in the water.And it goes without saying: thesurface you’re cleaning should bewatertight.
Who Is QualifWho Is QualifWho Is QualifWho Is QualifWho Is Qualified ied ied ied ied TTTTTo Do the o Do the o Do the o Do the o Do the WWWWWororororork?k?k?k?k?
Walk down any street, in any city, andyou’ll more than likely see good stonerehabilitation intentions gone bad …stone “rehabilitation” work that hascaused more harm than good. Atthe Acropolis in Athens, Greece, forexample, a botched 1930s marblerestoration project involved the use ofiron clamps that rusted over time,causing the structures to further crackand crumble. The outcome wasunfortunate and avoidable.
When it comes to stone rehabilitation,you can count on one thing. Whatyou don’t know will hurt you. It’sessential to work with designprofessionals and restorationcontractors who are knowledgeable,trained and experienced in restoringstone structures and surfaces.
Although deterioration in limestone andmarble is inevitable, there are ways toslow the process and prevent seriousdamage. Routine maintenance andinspections can reveal surface damage,displacement and joint failure that cansignify more serious underlyingconditions. Early detection andprompt, careful attention are key.
