Long-term study on failure mechanisms of exterior applied tilings

A durable outdoor tile installation requires good materials, a professional application and ideal climatic conditions. To unravel the mechanisms affecting an initial failure and its propagation under outdoor conditions, a long-term field experiment on floor and wall tilings was carried out. To provoke failures, recommendations were purposefully disregarded in pre-designated areas. Besides ceramic tiles, glass tiles were intercalated in the tilings to show accelerated failure evolution at the glass–mortar interface due to the smooth surface of glass and reduced associated adhesion. The tile–mortar or glass–mortar interfaces were found to be the mechanically weakest structures, where cracks due to shrinkage and thermal expansion occurred first. Through such newly formed pathways, water enters the system leading to local expansion owing to hygric swelling of the mortar or frost swelling of water in cracks. Cyclic loads weaken the system continuously; cracks propagate and widen. Initial failure occurred first on the glass tile system. With a delay of 1 year, the porcelain tile system also failed indicating that a similar failure evolution takes place in both systems. Thermal expansion and contraction as well as water percolation after each rainfall were found as major weakening processes of the system tile–mortar–substrate.