We are installing ceramic tile in my kitchen/dining and living rooms. The tile installers in my area (southwestern Ontario) inform me that tile is installed directly on sub-floor. (Sub-floor has already been layed - screwed on 4" grid). Enter mother-in-law (interior designer from Florida) who informs me that the tile needs to be lathed. I have contacted 6 independent tile installers in my area (including home depot in Toronto) who tell me that this method is no longer used - tile is installed on sub. Could you provide some guidance on this???