Subfloor preparation is the first thing you want to do in order to ensure that your tile is installed correctly — you do not want any subfloor movement or deflection. The Tile Shop offers a product called Blanke-PERMAT, a 2×3 mesh sheet weighing only one pound. You can install it right on top of the plywood subfloor for most stone installations. Another product is the cement boards, Permabase and Hardie Backer, which are both are made up of 90% Portland cement with some selective additives and resistant to mold and mildew.