Deterioration of Thin Marble Cladding - Infotile

installationFigure 1The new marble façade onFinlandia Town Hall –approximately 6 months after arecladding of the building.Deterioration ofThin Marble Claddinga major international studyby Bent Grelk Ramboll, Copenhagen, Denmark, Björn Schouenborg SP Swedish National Testing and ResearchInstitute, Borås, Sweden, Katarina Malaga SP Swedish National Testing and Research Institute, Borås, SwedenThis intriguing article reveals that problems can and do occur, even with materials like Carrara marbles that have been used extensively for manyyears. The article also confirms that solutions can be found and improvements can be made. There is no sense in assuming that everything in thegarden is rosy, when it patently is not. These images could be enough to deter any specifier from choosing thin marble as a cladding material.However, despite the cost of repairs and the apparent severity of the highlighted problem, the majority of marble façade installations performadequately. This article serves to highlight the critical need for architects to be well informed about the materials they have at their disposal, andhow and where they can be used effectively. This report was partially funded by the European Commission and conducted by TEAM (Testing andAssessment of Marble and Limestone).BackgroundNatural stone has been used for facade applications since timeimmemorial. Originally, the stone employed was rather thick, whenused as a construction element, and the strength and durability wasvery consistent . Scientific research on properties of marble began inthe late 19th century. In the years following, the thickness of naturalstones used on facades decreased from over 1000 mm (as inconstruction elements) to 20-50 mm (in cladding applications) as aresult of new cutting technologies and equipment that was developedby industry.The use of thin marble and limestone slabs as facade cladding hasincreased substantially during the last few decades.Even though the vast majority of marble claddings performsatisfactorily, durability problems began to occur, following the adventof thin cladding materials. During recent years reports of facade failureshave increased dramatically.Prominent buildings such as the Amoco building in Chicago, theFinlandia City Hall in Helsinki, La Grande Arch and SCOR Tower in Parisand IBM Tower in Brussels have all experienced serious problems withtheir thin marble clad facades. The problems include expansion,bowing, loss of strength, and in the most serious cases completedetachment from the anchoring system.The bowing of marble is not only restricted to buildings. Marbletombstones have also been known to bow. At the present time, mostof the recorded cases of façade failures emanate from Europe or NorthAmerica, because of the more widespread use of thin marble claddingsin those parts of the world. However, failures have also been recordedin Lebanon, Australia, India and Cuba.The problems regarding limestone facades are slightly different.Apparently, limestone does not bow, however it can expand causingserious problems if the joints are not sufficiently wide enough totolerate the expansion.The industry urgently needs to develop a repair system for existingfacades that develop problems. Despite several European researchprojects, the prime solution relies on replacing the panels at a cost ofapproximately 600-900 AUD $/m². The fairly recent example of theCity Hall in Helsinki, where all panels were replaced in 1998, came inat a cost of 6.5 Million AUD$ (a figure that was not dissimilar to theentire cost of the TEAM project). This provides an economicperspective of the problem. The problem did not cease because itwould appear that the new panels which were chosen incorrectlystarted to bow 6 months after installation! (Figure 1)It is estimated that the known cost of repairs to damaged facadeslocated in Europe will exceed AUD$400 million. This figure is based oncurrent strategies used to effect repairs. Although the vast majority ofreported durability problems with thin marble or limestone slabs relateto use of Italian Carrara marble, which is the most widely used marblein the world, other marbles e.g. American, Norwegian and Portuguesehave also been reported to bow on facades. However, the reports onperformance of Carrara marble are inconsistent, since in some casesCarrara marble apparently performs satisfactorily. Note that there areabout 200 different stone quarries in operation in Carrara, Italy! Thedirection of the observed bow may be either convex or concave relativethe facade, this is probably determined by local climatic conditions.issue 9 www.discoveringstone.com.au22

Figure 2A close-up of the bowedCarrara marble panels onFinlandia Town Hall fewmonths before the panelswere replaced by new Carraramarble panels.Figure 3 The townhall in Malmo,Sweden features a27 year old Carraramarble facade thatis in perfectcondition.However, despite considerable effort the exact physico-chemicalprocesses responsible for the degradation of thin marble and limestoneslabs exposed to outdoor conditions have not been established by theresearch community. As a consequence of the reported durabilityproblems and the lack of fundamental understanding of the problem,both producers and users (architects and building owners) of marbleand limestone are almost desperate for more knowledge and inparticular they are eager to find a test method that will distinguishdurable building stones from nondurable building stones.ObjectivesThe main objectives in the TEAM were:• To understand and explain the mechanisms of the expansion andloss of strength, probably the most important phenomena leading todegradation of marble and limestone clad facades.• To prevent the use of deleterious marble and limestone byintroducing drafts for European standards.• The project also aimed to develop a concept for assessment offacades, including a monitoring system in order to predict strengthdevelopment and improve safety and reliability.• To analyse if surface coating and impregnation could prevent ordiminish the degradation.• The project has also addressed quality control aspects in order tooptimise the production conditions.Work carried outThe TEAM project consortium, representing 9 EU countries, comprised16 partners representing stone producers and trade associations,testing laboratories, standardisation and certification bodies,consultants, building owners and care-takers and producers of fixingand repair systems.A state-of-the-art report has been written and is based on an extensivecompilation of more than 300 papers on marble and limestonedeterioration dating from late 1800s to 2005. A survey of about 200buildings has given a clear picture of the extent of the problem ingeographical, geological and climatic terms.Detailed case studies of 6 buildings have resulted in a methodology forassessment of facadesincluding monitoring system and risk assessment.Research, both in the laboratory and the field was performed on alarge number of different natural stones from various countriesutilised in varying climates. This provided an explanation ofdegradation mechanisms and lead to the determination of the criticalinfluencing factors.Two tests methods, including precision statements: one for bowing andone for thermal and moisture irreversible expansion have beenprepared for submission to CEN TC 246.Repair techniques based on the use of surface coating andimpregnation systems has been tested in the laboratory and in field.Positive side effects including increased durability and easier cleaninghave been observed.Guidelines for production and product control have been proposed. Aninstruction for stone sampling and description has been developed.Observation and results from the projectInspection and investigation of buildingsDuring the project a total of 194 Building Projects have been identifiedand reported on, providing various levels of detail. This includes 26Buildings that have been selected for further investigation.• All of the 26 Buildings were considered as suitable for dismantlingof the facade panels for laboratory testing purposes.• Six buildings were selected for detailed field studies, measurementsof bowing and supplementary investigations.• Two buildings were selected for long term monitoring.Based on the investigations we have concluded that the phenomenonof bowing of thin marble is actually rather common. Deformation bybowing is experienced in buildings of various ages, in buildingsexposed to various weather conditions and for slabs of variouswww.discoveringstone.com.au issue 923

installationthickness and dimensions and with different anchoring methods.Figure 4 Figure 5Finally, and what is most interesting, bowing is registered for marble ofseemingly different composition and structure.It is important to note that the problem of bowing is not restricted toone type of marble or one climatic zone. The buildings are situated inNorthern, Central and Southern Europe, and there are buildings withbowed slabs in all countries (Austria, Belgium, Denmark, Finland,France, Germany, Greece, Italy, Netherlands, Norway, Portugal, Spain,Sweden, Switzerland and United Kingdom). Many of the buildings withproblems have been visited and a preliminary investigation has beenconducted. During these investigations several different marble typesfrom Greece, Italy, Portugal, Spain, Norway and USA have beenidentified as having durability problems in terms of bowing.It is also equally important to draw attention to the fact that manymarble and limestone claddings and pavements tend to be durable androbust, provided that the correct quality has been specified.The report also considered the possible effects of climate.It isreasonable to discuss the effects of different locations of the stonefacade slabs on the building itself – height above the ground anddirections of the compass. As for these parameters, our studies are inaccordance with the literature:• most pronounced bowing on the upper parts of the buildings and• most pronounced bowing on the facades that face southeast andsouthwest. Pronounced bowing also occurs on facades that facesouth. The claddings facing to the north display less tendency to bow.This implies that the facades which are subjected to the most sunlightFigure 6Figure 7Figures 4-6 Examples from Croatia depict a building façade that exhibits severe bowing.Figure 7 Bowing measurement on a façade.MULTI-FUNCTIONALBULLNOSE MACHINE• Low cost, high efficiency, easy operating • Effective processing length: 3100mm• Easy to maintain• Effective processing height: 200mm• Ideal for processing all kinds of straight border, • Vertical and horizontal grindingplane line and curve border• Working head adjustment degree: 360• Automatic edge profile shape & polishing • Total power: 3.74kwBullnose from 20mm to 120mm thick• Price: $27,000 (excluding GST)Square edge up to 120mm thick• Free delivery Australia wide• Dimention: 3800mm X 1500mm X 1500mmwww.discoveringstone.com issue #700JY Diamond Tool Pty LtdPO Box 63, Moorabbin, Victoria 31892/26-28 Christensen St, Cheltenham, Victoria 3192Tel: (03) 9532 0268 Fax: (03) 9532 0242Toll free: 1800 999 893

installationexhibit the highest percentage of bowing panels and the largestamplitudes.• The bowing seems to be related to some types of marble andmarble/limestone while other stone types (travertine, slate, granite,sandstone etc) do not demonstrate this problem.• Both concave and convex bowing can occur on the same facadewith the same marble.• There is a clear correlation between bowing behaviour anddeterioration leading to loss of strength.• It cannot be stated that non-bowing stone slabs are notdeteriorating and loosing strength (e.g. mortised facade slabs seemto be hindered from bowing but might still deteriorate)• There are quite a few different types of marble (with various origins)that may bow. Marble selected from same region or even samequarry can demonstrate bowing as well as non-bowing behaviour.• Problems other than bowing and deterioration have been registeredand noted.• Marble types with known or measured bowing problems andmarked strength loss should be avoided in thin building claddings.Based on the observations it is also possible to conclude that revisionsin e.g.:• Application system (fixing methods)• Thickness of stone slabs• Panel face dimensions• Placement on the building may not totally hinder or reduce thedeterioration in such marbles.Investigations of selected buildings show large strength loss in theorder of 80 % after 35 years for one calcitic marble and 40 % for onedolomitic marble. Laboratory studies clearly indicate that there is nocorrelation between the amount of bowing and the loss of strength.This is especially worrying since there is a potential risk of severestrength loss without any evident bowing of claddings.It is surprising that, despite several reports of severe loss of strength,field investigations in relation to this topic are rare.Main ConclusionsThe TEAM project has significantly increased our knowledge of marbleand limestone deterioration processes.We hope that the findings will contribute to an increase in the use ofmarble and limestone for cladding and thus help restore some of thetrust lost in these materials in particular countries and climaticconditions. The main conclusions are given below:• A deeper understanding of the properties influencing the durabilityof marble and limestone as an outdoor cladding material has beengained, not the least through compiling and reviewing most of theliterature (over 300 articles) in this field and making it available toanybody through the homepage (see www.sp.se/building/team).• A comprehensive building survey, of about 200 buildings, has givena very good picture of the extent of the problem both geographicallyand geologically. Bowing is a worldwide phenomenon not confined toone type of marble or one type of climate, e.g. frosty conditions arenot necessary for this phenomenon to occur. Subsequent detailedcase studies have provided the possibility of testing severaldeterioration hypotheses and yielded important information aboutthe variables to be used in the test methods which were developedlater in the project, and are especially relevant to variations intemperature.• Sampling and testing of panels from the buildings have providedfurther information about the deterioration process and the rate of

installationFigure 9Figure 8 Bowed marble panelson a building in Helsinki,Finland.Figure 9 Microphoto (1.0x 1.5mm) Carrara marble withgranoblastic microstructure,marble with potential bowingbehaviour.Figure 10 Microphoto (1.0x1.5 mm) Carrara marble withxenoblastic microstructure. Amarble that does not bow.Figure 10change, together with the inspection methodology, this has provideda sound basis for building a model to predict the remaining servicelife, including analysis of the associated risk.• Long-term monitoring underlined the importance of repeatedmeasurements in order to enable reliable conclusions to be made.One time measurements are of little use due to large diurnal andseasonal variations.• The sampling of test materials is very critical for any project.Detailed sampling and sample marking instructions have to be usedfor any sampling. Our findings have been reported to CEN TC 246Natural Stone.• Laboratory testing of almost 100 different types of marble hastaken us much further in our search for the mechanism and allowedus to refute many “old” hypotheses. The main extrinsic influencingfactor is elevated temperature in the presence of a moisture gradient.This creates the external stresses that different marbles will thenrespond to in different ways. The most crucial intrinsic parameter isthe complexity of the grain boundaries and the grain size distributionof mineral grains in the rock. This provides different bonding strengthbetween the mineral grains due to the complexity of thearrangement of the grain boundary and in combination with thecrystal structure. The irregular grain structure that all marbleconsidered suitable for outdoor cladding have in common is theproduct of the metamorphism that turned limestone into a marblecombined with a dynamic recrystallisation event. Weaker bonds willcause granular de-cohesion, ’sugaring’, of the marble and significantstrength losses.• The work in developing the test methods has proved that everymarble is unique and has a unique response to climatic stresses withits own degradation curve. The acceleration factor of the laboratorybow-test is therefore different for different marble types. The testmethods developed enable a relevant evaluation that determineswhether a marble is suitable for outdoor cladding or not. The bowtestcan be adapted and used for predicting the remaining service lifeof a specific marble on a particular building.• Field exposures have shown that it is possible to inhibit or decreasethe degradation of marble by coating the surface with a hydrophobictreatment. The effect is most pronounced on marble already exposedand it should not be used to support the selection of an unsuitablemarble for a new building project.• Guidelines for designers and producers/suppliers have been givento ensure a proper selection of suitable marble and limestone foroutdoor cladding and to insure production with a homogeneous andacceptable quality respectively.AcknowledgementThe authors would like to thank the European Commission for financialsupport of the European research project “Testing and Assessment ofMarble and Limestone” (Contract no. G5RD-CT-2000-00233). The cooperationwith the project partners is gratefully acknowledged.Bent Grelk Ramboll Group, DenmarkBent Grelk is an experienced senior engineer at RAMBOLL Group, aconsultancy firm that has more than 4,000 employees at 70 offices.Bent Grelk is specialized within the fields of concrete technology,condition survey of concrete structures and facades clad with naturalstones. He is in charge of Ramboll’s main Concrete and MaterialLaboratory in Virum, Denmark. He is an expert witness appointed bythe Danish Court of Arbitration in cases concerning problems withnatural stone. Bent Grelk has extensive experience in concrete andnatural stone testing.(contact: bng@ramboll.dk see also: www.ramboll.dk )Björn Schouenborg SP Swedish National Testing and Research Institute, SwedenBjörn Schouenborg is RTD Manager of SPs department of BuildingMaterials. SP is a governmentally owned limited company withapproximately 600 employees covering a wide range of activities suchas testing, research and product and quality system certification. SP isalso the national metrology laboratory. Mr Schouenborg has a PhD inMineralogy & Petrology and has been in charge of all researchactivities concerning bedrock materials and related products at SP since1990. Mr Schouenborg is the co-ordinator of the EU project TEAM(Testing and Assessment of Marble and Limestone)(contact: bjorn.schouenborg@sp.se see also www.sp.se)Katarina Malaga SP Swedish National Testing and Research Institute, SwedenKatarina Malaga is senior scientist at SPs department of BuildingMaterials and is responsible for development, investigation and testingwithin the Technical Area Natural stones/Dimension stones. MrsMalaga has a PhD in Inorganic Chemistry and MSc in Geology and hasbeen involved in several national and international research activities(TEAM, OSNET, I-STONE among others).(contact: katarina.malaga@sp.se see also www.sp.se)issue 9 www.discoveringstone.com.au28