Subfloor preparation is going to be the first thing you want to do to make sure that your tile is installed correctly. You do not want any subfloor movement or deflection. The Tile Shop offers a product called Blanke-PERMAT. It is a 2×3 mesh sheet weighing only 1 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. They both are made up of 90% portland cement with some selective additives. They are both resistant to mold and mildew. For more information, go to TheTileShop.com.