CASTELL6N (SPAIN) <ii'QUALICC2Jl.,2000

WHY DOES FACADECERAMIC TILING FAIL?

Jonas Silvestre Medeiros

Dr Eng., C Eng., Professor at the Department of Civil Engineering Construction of thePolytechnic School of the University of Sao Paulo - Brazil

Av. Prof. Almeida Prado, Trav. 2, Ediffcio de Engenharia Civil,

Cidade Universitaria 05424 - 970 Sao Paulo - SP - Brazil

jonastpc@pcc.usp.br

ABSTRACT

Although ceramic tile manufacture and adhesive technology have achieved significantdevelopments throughout the years, ceramic tile facades still show a critical number of problems.It can be said, in some situations, that the number of pathologies has increased.

In this context, two main origins of problems arise: insufficient understanding ofinstallation technology and a lack of systematic approach in order to develop designing processesof ceramic tiling that take into consideration performance and durability.

Although we can consider that a number offeatures regarding ceramic tiling facades arestillnot very well understood - such as the actual stress level of each layer of the adhered system andthe amount of flexibility necessaryfor setting and grout materials - several guidelines can be usedin practice to contribute to the successful final performance of tiling.

The most common and severe problem offacade ceramic tiling is bond loss. This failure canbe related to three main different causes: inadequate specification of adhesive to each specificapplication, absence of control joints to dissipate stress and insufficient amount of adhesive toguarantee minimum coverage of tile reverse. While the first two factors are directly related to thedesign process, the third is associated with factors such as: tile-settling techniques, workmanshiptraining, use of correct tools and efficiency of quality control during execution.

This work shows examples of ceramic tiling facade failures and discusses major efforts toavoid them. Particular attention is dedicated to showing how designing is important to achieveexpected tiling performance. A comparison of problems and solutions also allows demonstratingthat ceramic tiling building facade demands more accurateand controlled methods of installationto guarantee suitable durability.

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Figure 1. View of buildillg facadewhere the bond bettoeen adhesiveand tile broke. Correction requiresremooing of tiles alld preparation

of surface whell cement-sendrendering remains adequate.

Figure 2. Detail shows bond installationproblem but tilillg also presents

inadequate joillt thickness, I/O control jointand very rigid adhesive mortar and grollt.

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1. INTRODUCTION

Brazil, like m any o therscountries in the world, has importantcharacteristics that recommend theuse of ceramic tiling sy stems.Ceramic tilings also have the bestcos t-benefit re la tionship amongsystems available in the market, mostof all if we con sider maintenancecosts. Nevertheless, many problemshave been occurring wi th ceramictile, particularly in high rise buildingfacade applications. These problemsare mainly related with appropriatedesign, installation techniques,p lanning, control and materialspecification.

As strange as it may sound,facade problems are growing innumber and consequences, clearlyshowing that technology developmentis urgent. Pathologies and buildingdefects are the visible face of ceramictiling application problems. Amongthese, rupture of substrate and bondingproblems deserve special attention,mostly due to risks of accidentsinvolved. Figures 1 to 6 show differentfeatures of the problems. These twoproblems can be considered criticalbecause of the three following features:

• lost of integrity is ge nerally ofthe entire tiling or substrate;

• correction is complex andexpensive;

• risks of accidents is involved .

On the other hand, if the tilingkeeps its expected performanceduring its life-time, many advantagesarise when comparing tilin g withother fini shing systems. The mostimportant advantages are: aesthetics,geometric facilit y of the composition,cleanability, improved dampresistance, general performance,economic value and durability.

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Figure 4. Cement­sand render substrate

shows rupture.Inadequate

specification of mortarwas considered mail/causehere. Creep ofconcreteframework

and differentialmooements of

masol/ry infillingCOl/ tribute to the

situation. There werehorizontal joints butthey were incorrectlu

positioned. -. _-: --- -

-

-

Figure 3. Tiles removed from thefacade show problem offixing.Inadequacu of setting togetherwith wrol/g specification ofmaterial caused failure.

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Figure 5. Herethe entire systemhas beenremoved. Thiscosts about 100% more thaninitial costs butthere was I/ O

other way to fixthe problem.

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.-< . •

. - .___ ' - : .~ 4 .. ...

.. - . -.;: ,. -.- - - -- . "- .-. - -

Figure 6. View of facade whereold ceramic tiling has beenremoved. Surfacecleaning wasIlecessary to allowil/g bondingneto layers.

2. CAUS ES OF TILING FAILURE.

A large number of cau ses can interfere in the mechani sm of tilin g failure. Among 17cases stud ied by the author, there are three cau ses that arise as the most important andcommon. These cau ses are discu ssed briefly in the following points.

2.1. ABSENCE OF CONTROL JOINTS

Positioning and sizing of control joints are very important to the performance offacade ceramic tiling. If adequately de signed , controls joints can di ssipate stressesgenerated from the exterior en vironment (temperature and humidity changes) and fromthe int erior of the building (creep, sh rinkage and other differential movements of thebackground). The number, size and po sitioning of joints depend on other severalvariables . The mo st important of the se are:

• size and colour of tile;

• modulus of elasticity of tile;

• flexibility of ad hes ives and grouts;

• sea lant Movement Accommodation Factor - MAF - as described in BS 6213 (1982);

• expe cted lon g term deformation of concrete framework (creep and shrinkage);

• amount of differential movement between framework and;

• ma sonry infillings, height of building.

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Buildings high er than 28 m usually require a horizontal joint at every floor level.Vertical joints are spe cially recommended for large panels without openings. These jointsare normally spaced betw een 5 to 10 m.

2.2. I SUFFICIE T AM O U T O F ADHESIVE TO GUARANTEE FULL COV ERAGE O FTILE.

Wh ile the previou s cause is related directl y to the designing process, lack ofadhesive coverage is more complex and associated w ith the follo wing main factors:

• tile-setting techniques;

• training of workmanship;

• use adequate tools;

• efficiency quality contro l during application.

Quality control of application is essential to the performance and durability ofcer ami c tiling. It invol ves design constructibility evaluation and fulfilment of techniquesand materi al use before, during and after the application process. Figures 7 and 8 showdi fferen ces between correct and wrong tile se tt ing techniques in adhesive cover age.

In faca de applications, tile-settling techniques are very important. In these cases,double fixing techniqu e is essential to achieve go od results. Double fixing se tting includesapplica tion of mortar on tile reverse and on subs tra te or background surface. Whenapplying mortar on surface, the tile fixer sho uld firs t use the flat edge then the notchededge of the trowel as shown in Figures 9 and 10.

Workman ship needs training according to the method spe cified in the design. Mo stp rojects involve parti cul ar techniques and therefore specific training is required. Trainingrarely exceeds a couple of hours whe n the contracto r is rea lly professional.

Figure 7. Lef t: f ull coverage whereaccurate setting was used. Right: the lack of adhesive materialoften causes failure. Technique, tools and quality control play an important role.

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Figure 8. Different tilefixers achievedifferellt results tolten training and

control are put into practice. Here thecoverage is not enougu. A facaderequires a 100% covered surface.

Figure 10. The notchededge of the trowel isused to prepare the surfacefor adequatefixing .

Horizontal stripes are preferable to avoideoentual water leakage.

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Figure 9. Adhesive mortar isspread first with the flat edge

of the trowel to guaranteecoverage of the background.III this case, a square shaped,Smm heiglzt notched trowel

was used.

Figure 11. Tiles are positioned byoffsettillg them from their final place so

the adhesive call be fu lly spread. Thetechnique is very simple but gives good

results to improve coverage.

Figure 12. The tiles are pressed «gains:the background, not ollly to improve

coveragebut also to prcuent slippillg. Thematerial is isotropic and squeezes whell

pressed by percussion.

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Figure 13. [oint cleaning isvery important to let the

grout fill the jointscompletely. Herea

brush is used.

Figure 14. View of thecleaned ceramic tiling, readyfor the application ofjoint

grout.

---

Figure 15. A rubber troweldesignedfor joillting is used

herefor adequatefilling.

Figure 17. Secondarycleaning of the tiling

surface. Beyond this steponly final cleaning is

required.

Figure 16. Primarycleaning of grout that spillsout of the joint and remains

011 the surface of tiles. Asponge is used.

Figure 18. Back-up tape isused to avoid sealant

bonding to the backof thecontrol joint. The technique

is essential to sealantbehaviour and durability.

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Figure 19. Sealant is applied ill thecontrol ioint, Jointillg is necessary afterthe preset time of the material. Note that

tape used to protect tile edges.

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Tools are an important part of theapplication method and their correctutilisation depends also on training. Thetrowel is the most important tool inceramic tiling but mixers and brushesplay an important role too. Adhesives andgrou ts must be mechanically mi xed andjoint grouting requires previous accuratecleaning. The height and sh ape of th eteeth are important parameters for th eadequate selection of the trowel. Figure 11to 19 show s some fea tu re s of th eapplication method .

2.3.1 ADEQUATE SPECIFICATIO OFADHE9VEANDGROUT

The most important properties of adhesives and grouts for ceramic tiling are bondresi stance and flexibility. Open time is also an important property of adhesive mortar,however its importance varies a lot according to tile sett ing technique, training andquality control. Bond resistance can be evaluated through pull-out and shear tests, butpull out is simpler and reproducible. Is can also be done at the work site and is prescribedby Brazilian standards. (AB T, 1998).

Although th e flexibility specification and evaluation are full of controversy,there is a clear and easy procedure prescribed by UEAtc (1990 ) to test it. Several dif­ferent adhesive mortars w ere tested according this method, show ing very goodresults. Table 1 proposed initially by MEDEIROS (1999) suggests a possible cla ssifica­tion of these materials according to the deformation of the specimen under the testprocedure.

FLEXIBILITY MINIMUM SPECIMEN DEFORMATIONCLASS BEFORE CRACKING (mm)

1 1,5 to 2,0

2 2,0 to2,5

3 2,5to3,5

4 3,5to4,5

5 > 4,5

Table 1. Proposed claseification of adhesive mortar based all theflexibility test prescribed by UEAtc (1990).

Specimen preparation is shown in Figure 20. The apparatus shown in Figure 21 wasdeveloped specifically for thi s purpose. Classes 3 to 5 are adequate for exterior use. Theclas sification can also be used for the selection of grouts.

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Figure 20.Flexibility test

specimen isunder

preparation.Mouldillg thespecimen ill-

groups avoidsdeviation ofresults. Thespecimen is

simple to prepareand showed good

results asdescribed by

M EDEIROS etal. (1998).

Figure 21.The apparatusshowllwasdesign ed andbuilt to maketheflexibilitytest easier andcheap. Goodsresults showeditsapplicability.The apparatuscosts aboutUS$ 1,000.

3. CONCLUSION

The genesis of ceramic tiling problems lies in the designing process. It includesmaterial and application technique specification, training and controlling criteriadefinition. Appropriate designing and application are fully worthwhile when themaintenance cost is take into consideration.

Several experiences conducted by the author over the last few years showed that thetotal cost of well designed, planned and controlled ceramic tiling increases from 10 to 25%when compared to a risky situation. The correction costs of defects and pathologies canexceed 100 % of the initial costs. Construction companies should consider theirinstitutional image, market credibility, risks of accidents and the insurance costs involved.

All the information necessary for an adequate application of facade ceramic tilingcan be set in order by design. If correctly and systemically understood it plays a veryspecial role, serving as an essential tool for application. (MEDEIROS, 1999)

The author suggests below a list of research themes that can be consideredimportant for the technology development of ceramic tiling in order to avoid the presentproblems. Those are:

• Influence of polymer and cement type and content in the flexibility of adhesivemortars;

• Performance of joint grouts: lab and field tests;

• Influence of workmanship in the performance of ceramic tiling;

• Quality control methods for facade application;

• Use of crack suppression membranes in facade ceramic tiling;

• Prediction of movements in facade ceramic tiling;

• Method of analysis of stress of ceramic tiling layers;

• Definition of criteria for the design of ceramic tiling control joints;

• Maintenance of ceramic tiling: techniques and methods.

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4. REFEREN CES

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[1] ABNT - ASSOCIA<;:AO BRASILEIRADE ORMAS TECNICASArgamassa colonie industrializada pam assentameniode placas de cl'ra­mica- deierminaciio da resis tencia de aderencia - BR 14084. Rio de Jan eiro, 1998.

[2) BRITISHSTANDARDS INSTITUTION. Guide toselectionofconstructional sealants - BS 6213, amend me nt n. 1, 1982. Londo n, 1982.

[3] MEDEIROS, J.5.; SABBATl I EH, AKIAMA, S. Y. Flexibilidad de morieros adhesioos. En: Cong reso Mund ial de la Ca lida d delAzulejo y del Pavirnento Cera rnico, 5., Cas tellon, 1998. QUALICER 98. Castellon, 1998. v.2, p.GII-3-11.

(4) MEDEIROS, J.S. Tecnologia c projeto de reuestimentos ceramicos de[acliadade edlficios.Tese (douto rado) . Escola Politecni ca ­Uni versid ad e de Sao Paulo. 1999. 458 p.

[5J UEATC - UNION EUROPEEN POUR L'AGREMENT TECH IQUE DANS LA CONSTRUCTION. Techniciam Guide for the Assessmt'llt ofCeramic Tile Adhesives - Cahier s du CSTB, issue 311, cahier 2435. 1990.

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