We had our material tested to ASTM C627 (the Robinson Floor Test) to see how suitable our system was for application under tile. Tile has very little tolerance for any deflection or movement of the surface to which it is installed. Too much deflection or if the membrane beneath is too soft may cause cracking of the gout lines or the tile. Tested over 3/4 inch plywood and 1/2 cement board, porcelain tile on Tiledek achieved a "heavy" rating with no cracking of tile or grout lines after 9000 revolutions with 600 pounds on steel wheels (on the twelfth cycle). This is much more than would ever be necessary for residential traffic on a roof deck. On the same subsurface assembly, we achieved a "residential" rating on slate. There were no signs of cracking on the slate or the grout line. The failure was in the slate itself which showed signs of the surface deteriorating where the steel wheels made contact. On 3/4 inch plywood covered with Tiledek plus a layer of Schluter's Ditra mat, we achieved a "residential" rating.