How to Lay a Stone Tile Floor

Spread unmodified thinset over an area about 3 feet by 16 inches, filling the membrane's square dimples. Comb out parallel ridges with the notched trowel. For each tile, smear thinset on its underside, press it firmly in place, and make sure it's flush with its neighbors and that the joints are even. Gently remove excess thinset from the joints with a putty knife, and swab the stones with a damp sponge.