Spatially resolved evolution of adhesion properties of large porcelain tiles

The rising number of failures of porcelain tiles, especially in outdoor applications, is to some extent a consequence of the critical combination of applying tiles of large dimensions and the non-porous nature of these tiles. A special setup allows a reproducible application of large-sized tiles (30 × 30 cm). In analogy to outdoor conditions, samples were stored under dry and wet conditions and have been investigated with different physico-chemical approaches. Under dry storage conditions adhesion strength is significantly lower along the periphery of the tiles compared to their centre. This reduction in adhesion performance is mainly caused by shrinkage of the mortar and substrate (∼0.1 mm/m). In situ observations through glass tiles indicate that the stresses induced by shrinkage are highest in the rim regions of the tiles. Under wet storage conditions, water percolates into the rim regions of the mortar, which leads to swelling of mortar and substrate, accelerating the delamination process. The findings of this study confirm observations on the construction site, where initial failures are often found at the periphery of large-sized tiles.