Effect of cyclic curing conditions on the tensile bond strength between the polymer modified mortar and the tile

Cementitious tile adhesive is a typical polymer-modified mortar, whose tensile bond strength is strongly affected by its curing conditions. Tile-back glue, a composite based on polymer emulsion, is a key role that used to improve the bond strength between the mortar and the tile. In this work, 4 artificial cyclic curing regimes with designed conditions were used to simulate the natural curing, and a constant curing was set as reference. Taking tiles coated with back glue as substrates, the tensile bond strengths of the VAE (vinyl acetate-ethylene) or SAE (styrene-acrylic ester) modified mortar with VAE or SAE content of 0 %, 3 %, 6 %, 9 % and 12 % were investigated. The results show that higher content of polymers, higher strength would be obtained under low RH cyclic curing, but it is different under high RH cyclic curing. Low RH cyclic curing improves the strength, while high RH cyclic curing generally inhibits the strength development of the polymer modified mortars. The results from SEM show that the added polymer forms a continuous film network structure at the mortar-tile interface region, thus significantly increases the strength with content increase under low RH cyclic curing. Furthermore, it was found that the morphology and distribution of the generated film network are seriously influenced by the experienced cyclic curing conditions, which have significant impact on the tensile bond strength of the cured mortar, especially in cases of the VAE modified mortars. Additionally, the given cyclic curing reduces the contents of AFt in the hydration products, while in the most cases, the contents of CH increase.