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Factors affecting ceramic tile adhesion for external cladding
Construction and Building Materials 13 Ž1999. 293]296
Factors affecting ceramic tile adhesion for external cladding M.Y.L. Chew 1 School of Building and Real Estate, National Uni¨ ersity of Singapore, 10 Kent Ridge Crescent, 119260 Singapore, Singapore Received 25 September 1998; received in revised form 26 April 1999; accepted 2 May 1999
Abstract The effect of the exposure temperature during and after the application of a tiling system on the development of bond strength of the adhesive was evaluated. It was shown that adhesive with approximately 50% of the water replaced by a polymer latex has the most consistent performance in the achievement of bond strength. Adhesive with 100% of the water replaced by a polymer latex was found to dry up too rapidly to allow sufficient time for the adhesive to interact with the substrate at the adhesiversubstrate interface. The results reflect the importance of a proper mix design especially when works have to be carried out under hot and dry weather. The effects of moisture and movement due to shrinkage and creep are also discussed. Q 1999 Elsevier Science Ltd. All rights reserved. Keywords: Tile; Bond; Polymer; Movement joints; Workmanship
1. Introduction A tile system for external cladding comprises the tiles, a substrate, a necessary fixative to adhere the tiles on to the substrate Žadhesive., and a grouting material to seal the pointing gaps between the tiles ŽFig. 1.. Although normally designed as non-loadbearing, such a system always responds to the environment with differential movements due to its composite nature. For example, tiles are inclined to have an irreversible moisture expansion, while its cementitious substrate, on the contrary, tends to permanently shrink on drying. If the bonding strength between the different constituents is sufficient, the tendency of the differential movements may be constrained, causing high build-up of stresses and possible damages in weaker constituents of the system. In other cases where the bond strength is weak, more differential movements may realise, leading
1 U
Tel.: q65-874-3496; fax: q65-775-5502 E-mail address: [email protected] ŽM.Y.L. Chew.
to a disintegration of the composite system at the interface between the layers w1]3x. The common causes for wall tile failures are: 1. deformation of adhesive Žor mortar. onto which the tiles have been laid due to shrinkage, etc.; 2. differential movements between the tile, adhesive and the immediate substrates, due to thermal, moisture or other effects; 3. failure of the cement rendering behind the adhesive; 4. structural movements, shrinkage and creep, vibrations and settlement problems; 5. improper surface preparation such as inadequate cleaning, no provision of proper keys; 6. improper design and selection of materials; and 7. improper sequence of work. A detailed analysis of the important factors causing adhesion failures is critical for a proper design and construction strategy to prevent the problem from occurring. The objectives of this study are to study the
0950-0618r99r$ - see front matter Q 1999 Elsevier Science Ltd. All rights reserved. PII: S 0 9 5 0 - 0 6 1 8 Ž 9 9 . 0 0 0 2 3 - 9
294
M.Y.L. Chew r Construction and Building Materials 13 (1999) 293]296
Fig. 3. Shear test setup.
Fig. 1. A typical tile system.
effect of temperature and movements on adhesive strength.
2. The effect of temperature extremes on bond strength To test for bond strength, a direct pull-off test was initially attempted. In this test, a groove Ž50-mm diameter. was first cored through the tiling system approximately 3 mm in depth into the concrete substrate, a steel plate was then fixed onto the area using a high-strength, fast-setting adhesive. A jack was then used to test the strength required to fail the tiling system and the failure mode visually observed ŽFig. 2.. The test was later found inadequate, as the bond
Fig. 2. Pull-off tester.
strengths of all tiling systems tested were found to be significantly affected by the coring process, no matter how slowly the coring was executed. An indirect shear strength test as shown in Fig. 3 was employed instead. A commercial tile Ž100 = 100 mm2 . was adhered to a concrete substrate Ž152 = 114 = 51 mm2 .. The concrete substrates used in this entire project were 38 MPa concrete with a waterrcement ratio of 0.4. The concrete substrates were moist-cured for 7 days and then air-cured for approximately 6 months to allow most of the shrinkage to take place w4,5x. Four types of commercial adhesives ŽAdhesive A, B, C and D. were tested. Adhesive A is a mixture of quickset cement with fine aggregate sand and water with a cement:sand:water ratio of 1:4:0.8. X-ray diffraction analysis reviewed that the sand is composed of 50% of a-quartz, 20% of K-feldspar, 10% of mica and 21% of mixed layered clay. Adhesive B is based on Adhesive A but with 50% of the water replaced with a commercial polymer Žacrylic with 35% solid content. as additive. Adhesive C is a mixture of quickset cement with fine aggregate sand and water with a cement: sand:water ratio of 1:3:0.4. Adhesive D is based on Adhesive C but with 100% of the water replaced with the same polymer as additives. For each type of adhesive, nine specimens were prepared under room temperature. After 3 days, three specimens were held at 258C, three at 608C and three at y108C. The specimens were held at their respective temperatures for 3 days, and were then allowed 24 h to return to room temperature before tests on bond strength were carried out. The results of the tests are summarised in Fig. 4. From the results, it was observed that under ambient
Fig. 4. Temperature vs. shear stress.
M.Y.L. Chew r Construction and Building Materials 13 (1999) 293]296
conditions, Adhesive B attained a 10% higher in shear stress than Adhesive A. This increase in bond strength for Adhesive B was expected due to the inclusion of polymer as an additive Ž50% replacement of water in this case.. The same trend was not found for Adhesive C and D. Adhesive D with 100% replacement of water with a polymer as an additive attained an 8% lower shear stress than Adhesive C. The lower bond strength of Adhesive D was believed to be due to the mix drying out too rapidly, even under the laboratory conditions. It is also believed that the polymerrcement ratio of Adhesive D may be too high. For specimens stored under the higher temperature Ž608C., the inclusion of polymer appeared to have favourable effects on the bond strength of the adhesives. An increase of 46% in bond strength was found with specimens using Adhesive B when compared with specimens using Adhesive A. An increase of 28% in bond strength was found with specimens using Adhesive D when compared with specimens using Adhesive C. This marked increase in bond strength, among specimens using adhesives with the inclusion of polymer as additive, stored under high temperature, is believed to be due to two main reasons. Firstly, under the higher storage temperature, a rapid strength gain was achieved due to the accelerated process of hydration. Secondly, it is known that optimum strength in most polymer modified mortar is obtained by achieving a reasonable degree of cement hydration under wet conditions at early ages, followed by dry conditions to promote a polymer film formation due to coalescence of the latexes. Thus, with the reduction of the capillary water, especially near the interface between the adhesive and the concrete substrate, the polymer particles flocculate to form a continuous close-packed layer of polymer particles on the surfaces of the gel-unhydrated cement particle mixtures and simultaneously adhere to the mixtures and the silicate layer over the aggregate surfaces. With water withdrawal by cement hydration Žaccelerated due to the higher storage temperature., the close-packed polymer particles on the cement hydrates coalesce into continuous films or membranes, and the films or membranes bind the cement hydrates together to form a monolithic network in which the polymer phase interpenetrates throughout the cement hydrate phase w6x. For specimens stored under lower temperature Žy108C., Adhesive B attained a 7% higher bond strength than Adhesive A whereas Adhesive C attained a 6% higher bond strength than Adhesive D. Although specimens using Adhesive B appeared to have increased the bond strength when compared with specimens using Adhesive A, the increase was marginal.
295
From Fig. 4, it can be seen that specimens stored under the lower temperature suffered from low bond strength being attained. From the results, it appears that for specimens using adhesives with no polymer, those stored under the normal condition attained the highest bond strength while those stored under the lower temperature attained the lowest bond strength. For specimens using adhesives with the inclusion of polymer as additive, those stored under the higher temperature attained the highest bond strength and, conversely, those stored under the low temperature attained the lowest bond strength.
3. The effect of temperature during application on bond strength The same type of tile and adhesives as in the previous section were used. Three specimens were glued at 108C, three at 258C and three at 408C and were held at the gluing temperature for 6 h. The specimens were then stored under ambient conditions for 8 days before shear tests were carried out. The results of the tests are summarised in Fig. 5. It was found from the results that for specimens glued at 408C, those using Adhesive B attained a 23% higher bond strength than those using Adhesive A. Specimens using Adhesive C attained a 21% higher bond strength than specimens using Adhesive D. For specimens glued at 108C, those using Adhesive B attained a 11% higher bond strength than those using Adhesive A. Specimens using Adhesive C attained a 7% higher bond strength than specimens using Adhesive D. In all cases, with or without the inclusion of polymer as additive, application at 408C and 108C reduced the bond strength from 10% to 47%. For all types of adhesive, application at a higher temperature appeared to have affected the bond strength more severely than application at a lower temperature. This is believed to be due to the concrete substrate surface being too dry Žpreheated to 408C and
Fig. 5. Temperature vs. shear stress.
296
M.Y.L. Chew r Construction and Building Materials 13 (1999) 293]296
maintained for 24 h in an oven., which can rapidly absorb the moisture from the adhesive matrix when applied and can hinder the hydration process. The lower bond strength attained by specimens applied under low temperature can be explained using the same principle but in reverse. The concrete substrate surface being too wet Žpre-cooled to 108C and maintained for 24 h in a freezer., can prevent the adhesive matrix from penetrating into the substrate, which can hinder the formation of a good bond. It is thus not surprising to find out that in the shear test, most failure occurred between the adhesive and the substrate interface.
4. Conclusions The effect of temperature during application on the development of bond strength is significant. Application at 408C and 108C was found to have reduced the bond strength from 10% to 47%. The inclusion of a polymer was found to play an important role in the bond strength development. However, depending on the application, the polymerrcement ratio requires careful assessment. For example, in the case of Adhesive B, which is based on Adhesive A but with 50% of the water replaced with a polymer latex, an 11% higher bond strength was attained compared with Adhesive A. However, Adhesive D, which is based on Adhesive C but with 100% of the water replaced with a polymer latex, was found to attain a lower bond strength than Adhesive C.
The storage temperature also plays an important role in the bond strength development although not as marked. It was found that for specimens using adhesives with no polymer, i.e. Adhesive A and Adhesive C, those stored under the normal condition Ž258C. attained the highest bond strength while those stored under the lower temperature Žy108C. attained the lowest bond strength. For specimens using adhesives with the inclusion of polymer, i.e. Adhesive B and Adhesive D, those stored under the higher temperature Ž608C. attained the highest bond strength and those stored under the low temperature Žy108C. attained the lowest bond strength. An increase of 46% in bond strength was found with specimens stored at below 608C using Adhesive B when compared with specimens using Adhesive A. References w1x Chew MYL, Wong CW, Kang LH. Building facades}a guide to common defects in tropical climates. World Scientific, 1998. w2x Chew MYL. Durability of building facades under tropical conditions. Final report. National University of Singapore, 1996. w3x Chew MYL. The use of infra-red thermography for assessing tile delamination. J Real Estate Construct 1998;8Ž1.:35]42. w4x BS6431. Ceramic floor and wall tiles. British Standard Institution, 1984. w5x Singapore Standard CP68. Code of practice for ceramic wall and floor tiling. Singapore Productivity and Standards Borad, 1997. w6x Ohama Y, Demura K, Nagao H. Adhesion of polymer modified mortars to ordinary cement mortar by different test methods. Adhesion between polymer and concrete. Symposium organised by Rilem Technical Committee 52, 1986.
Factors affecting ceramic tile adhesion for external cladding M.Y.L. Chew 1 School of Building and Real Estate, National Uni¨ ersity of Singapore, 10 Kent Ridge Crescent, 119260 Singapore, Singapore Received 25 September 1998; received in revised form 26 April 1999; accepted 2 May 1999
Abstract The effect of the exposure temperature during and after the application of a tiling system on the development of bond strength of the adhesive was evaluated. It was shown that adhesive with approximately 50% of the water replaced by a polymer latex has the most consistent performance in the achievement of bond strength. Adhesive with 100% of the water replaced by a polymer latex was found to dry up too rapidly to allow sufficient time for the adhesive to interact with the substrate at the adhesiversubstrate interface. The results reflect the importance of a proper mix design especially when works have to be carried out under hot and dry weather. The effects of moisture and movement due to shrinkage and creep are also discussed. Q 1999 Elsevier Science Ltd. All rights reserved. Keywords: Tile; Bond; Polymer; Movement joints; Workmanship
1. Introduction A tile system for external cladding comprises the tiles, a substrate, a necessary fixative to adhere the tiles on to the substrate Žadhesive., and a grouting material to seal the pointing gaps between the tiles ŽFig. 1.. Although normally designed as non-loadbearing, such a system always responds to the environment with differential movements due to its composite nature. For example, tiles are inclined to have an irreversible moisture expansion, while its cementitious substrate, on the contrary, tends to permanently shrink on drying. If the bonding strength between the different constituents is sufficient, the tendency of the differential movements may be constrained, causing high build-up of stresses and possible damages in weaker constituents of the system. In other cases where the bond strength is weak, more differential movements may realise, leading
1 U
Tel.: q65-874-3496; fax: q65-775-5502 E-mail address: [email protected] ŽM.Y.L. Chew.
to a disintegration of the composite system at the interface between the layers w1]3x. The common causes for wall tile failures are: 1. deformation of adhesive Žor mortar. onto which the tiles have been laid due to shrinkage, etc.; 2. differential movements between the tile, adhesive and the immediate substrates, due to thermal, moisture or other effects; 3. failure of the cement rendering behind the adhesive; 4. structural movements, shrinkage and creep, vibrations and settlement problems; 5. improper surface preparation such as inadequate cleaning, no provision of proper keys; 6. improper design and selection of materials; and 7. improper sequence of work. A detailed analysis of the important factors causing adhesion failures is critical for a proper design and construction strategy to prevent the problem from occurring. The objectives of this study are to study the
0950-0618r99r$ - see front matter Q 1999 Elsevier Science Ltd. All rights reserved. PII: S 0 9 5 0 - 0 6 1 8 Ž 9 9 . 0 0 0 2 3 - 9
294
M.Y.L. Chew r Construction and Building Materials 13 (1999) 293]296
Fig. 3. Shear test setup.
Fig. 1. A typical tile system.
effect of temperature and movements on adhesive strength.
2. The effect of temperature extremes on bond strength To test for bond strength, a direct pull-off test was initially attempted. In this test, a groove Ž50-mm diameter. was first cored through the tiling system approximately 3 mm in depth into the concrete substrate, a steel plate was then fixed onto the area using a high-strength, fast-setting adhesive. A jack was then used to test the strength required to fail the tiling system and the failure mode visually observed ŽFig. 2.. The test was later found inadequate, as the bond
Fig. 2. Pull-off tester.
strengths of all tiling systems tested were found to be significantly affected by the coring process, no matter how slowly the coring was executed. An indirect shear strength test as shown in Fig. 3 was employed instead. A commercial tile Ž100 = 100 mm2 . was adhered to a concrete substrate Ž152 = 114 = 51 mm2 .. The concrete substrates used in this entire project were 38 MPa concrete with a waterrcement ratio of 0.4. The concrete substrates were moist-cured for 7 days and then air-cured for approximately 6 months to allow most of the shrinkage to take place w4,5x. Four types of commercial adhesives ŽAdhesive A, B, C and D. were tested. Adhesive A is a mixture of quickset cement with fine aggregate sand and water with a cement:sand:water ratio of 1:4:0.8. X-ray diffraction analysis reviewed that the sand is composed of 50% of a-quartz, 20% of K-feldspar, 10% of mica and 21% of mixed layered clay. Adhesive B is based on Adhesive A but with 50% of the water replaced with a commercial polymer Žacrylic with 35% solid content. as additive. Adhesive C is a mixture of quickset cement with fine aggregate sand and water with a cement: sand:water ratio of 1:3:0.4. Adhesive D is based on Adhesive C but with 100% of the water replaced with the same polymer as additives. For each type of adhesive, nine specimens were prepared under room temperature. After 3 days, three specimens were held at 258C, three at 608C and three at y108C. The specimens were held at their respective temperatures for 3 days, and were then allowed 24 h to return to room temperature before tests on bond strength were carried out. The results of the tests are summarised in Fig. 4. From the results, it was observed that under ambient
Fig. 4. Temperature vs. shear stress.
M.Y.L. Chew r Construction and Building Materials 13 (1999) 293]296
conditions, Adhesive B attained a 10% higher in shear stress than Adhesive A. This increase in bond strength for Adhesive B was expected due to the inclusion of polymer as an additive Ž50% replacement of water in this case.. The same trend was not found for Adhesive C and D. Adhesive D with 100% replacement of water with a polymer as an additive attained an 8% lower shear stress than Adhesive C. The lower bond strength of Adhesive D was believed to be due to the mix drying out too rapidly, even under the laboratory conditions. It is also believed that the polymerrcement ratio of Adhesive D may be too high. For specimens stored under the higher temperature Ž608C., the inclusion of polymer appeared to have favourable effects on the bond strength of the adhesives. An increase of 46% in bond strength was found with specimens using Adhesive B when compared with specimens using Adhesive A. An increase of 28% in bond strength was found with specimens using Adhesive D when compared with specimens using Adhesive C. This marked increase in bond strength, among specimens using adhesives with the inclusion of polymer as additive, stored under high temperature, is believed to be due to two main reasons. Firstly, under the higher storage temperature, a rapid strength gain was achieved due to the accelerated process of hydration. Secondly, it is known that optimum strength in most polymer modified mortar is obtained by achieving a reasonable degree of cement hydration under wet conditions at early ages, followed by dry conditions to promote a polymer film formation due to coalescence of the latexes. Thus, with the reduction of the capillary water, especially near the interface between the adhesive and the concrete substrate, the polymer particles flocculate to form a continuous close-packed layer of polymer particles on the surfaces of the gel-unhydrated cement particle mixtures and simultaneously adhere to the mixtures and the silicate layer over the aggregate surfaces. With water withdrawal by cement hydration Žaccelerated due to the higher storage temperature., the close-packed polymer particles on the cement hydrates coalesce into continuous films or membranes, and the films or membranes bind the cement hydrates together to form a monolithic network in which the polymer phase interpenetrates throughout the cement hydrate phase w6x. For specimens stored under lower temperature Žy108C., Adhesive B attained a 7% higher bond strength than Adhesive A whereas Adhesive C attained a 6% higher bond strength than Adhesive D. Although specimens using Adhesive B appeared to have increased the bond strength when compared with specimens using Adhesive A, the increase was marginal.
295
From Fig. 4, it can be seen that specimens stored under the lower temperature suffered from low bond strength being attained. From the results, it appears that for specimens using adhesives with no polymer, those stored under the normal condition attained the highest bond strength while those stored under the lower temperature attained the lowest bond strength. For specimens using adhesives with the inclusion of polymer as additive, those stored under the higher temperature attained the highest bond strength and, conversely, those stored under the low temperature attained the lowest bond strength.
3. The effect of temperature during application on bond strength The same type of tile and adhesives as in the previous section were used. Three specimens were glued at 108C, three at 258C and three at 408C and were held at the gluing temperature for 6 h. The specimens were then stored under ambient conditions for 8 days before shear tests were carried out. The results of the tests are summarised in Fig. 5. It was found from the results that for specimens glued at 408C, those using Adhesive B attained a 23% higher bond strength than those using Adhesive A. Specimens using Adhesive C attained a 21% higher bond strength than specimens using Adhesive D. For specimens glued at 108C, those using Adhesive B attained a 11% higher bond strength than those using Adhesive A. Specimens using Adhesive C attained a 7% higher bond strength than specimens using Adhesive D. In all cases, with or without the inclusion of polymer as additive, application at 408C and 108C reduced the bond strength from 10% to 47%. For all types of adhesive, application at a higher temperature appeared to have affected the bond strength more severely than application at a lower temperature. This is believed to be due to the concrete substrate surface being too dry Žpreheated to 408C and
Fig. 5. Temperature vs. shear stress.
296
M.Y.L. Chew r Construction and Building Materials 13 (1999) 293]296
maintained for 24 h in an oven., which can rapidly absorb the moisture from the adhesive matrix when applied and can hinder the hydration process. The lower bond strength attained by specimens applied under low temperature can be explained using the same principle but in reverse. The concrete substrate surface being too wet Žpre-cooled to 108C and maintained for 24 h in a freezer., can prevent the adhesive matrix from penetrating into the substrate, which can hinder the formation of a good bond. It is thus not surprising to find out that in the shear test, most failure occurred between the adhesive and the substrate interface.
4. Conclusions The effect of temperature during application on the development of bond strength is significant. Application at 408C and 108C was found to have reduced the bond strength from 10% to 47%. The inclusion of a polymer was found to play an important role in the bond strength development. However, depending on the application, the polymerrcement ratio requires careful assessment. For example, in the case of Adhesive B, which is based on Adhesive A but with 50% of the water replaced with a polymer latex, an 11% higher bond strength was attained compared with Adhesive A. However, Adhesive D, which is based on Adhesive C but with 100% of the water replaced with a polymer latex, was found to attain a lower bond strength than Adhesive C.
The storage temperature also plays an important role in the bond strength development although not as marked. It was found that for specimens using adhesives with no polymer, i.e. Adhesive A and Adhesive C, those stored under the normal condition Ž258C. attained the highest bond strength while those stored under the lower temperature Žy108C. attained the lowest bond strength. For specimens using adhesives with the inclusion of polymer, i.e. Adhesive B and Adhesive D, those stored under the higher temperature Ž608C. attained the highest bond strength and those stored under the low temperature Žy108C. attained the lowest bond strength. An increase of 46% in bond strength was found with specimens stored at below 608C using Adhesive B when compared with specimens using Adhesive A. References w1x Chew MYL, Wong CW, Kang LH. Building facades}a guide to common defects in tropical climates. World Scientific, 1998. w2x Chew MYL. Durability of building facades under tropical conditions. Final report. National University of Singapore, 1996. w3x Chew MYL. The use of infra-red thermography for assessing tile delamination. J Real Estate Construct 1998;8Ž1.:35]42. w4x BS6431. Ceramic floor and wall tiles. British Standard Institution, 1984. w5x Singapore Standard CP68. Code of practice for ceramic wall and floor tiling. Singapore Productivity and Standards Borad, 1997. w6x Ohama Y, Demura K, Nagao H. Adhesion of polymer modified mortars to ordinary cement mortar by different test methods. Adhesion between polymer and concrete. Symposium organised by Rilem Technical Committee 52, 1986.