The adhesive differs on the type of tile or stone we are installing, for natural stone and porous stone we generally use a white cement based flexible rapid setting fixative. Tiling onto a concrete screed for example using porcelain or ceramic tiles, a grey cement based product is sufficient and more cost effective especially when covering larger areas. Wall tiling and wet rooms, we use a waterproof cement based adhesive which has the flexible additive- this enables us to tile onto ply boarded areas.