One of the most important steps when installing flooring in any type of renovation is to ensure that there is a clean and level surface where you will be applying your new flooring materials. Many times this means dealing with the sub-flooring that is exposed after removing the old flooring material. When removing old tile floors there will be some type of adhesive mastic or mortar that was used to attach the tile to the subfloor material. As the tile is removed it is likely that some of this adhesive material will be removed with the tile and some of it will remain adhered to the subfloor surface. In many cases the two materials will be a subfloor of plywood and thinset mortar as the adhesive. In order to use the plywood subfloor as the base for the new floor installation it will be necessary to remove all of the thinset mortar from the plywood.
Put on the dust mask and eye protection. Loosen the thinset by striking it with the hammer. Strike the thinset hard enough to crack it or break it free from the surface of the plywood but avoid using enough force to actually dent the plywood underneath the thinset.
Scrape thinset off the plywood using floor scraper. It is best to start scraping in a spot where the thinset has been loosened by the hammering and you can get the sharp edge of the blade on the surface of bare plywood and scrape into and under any thinset that is still bonded to the plywood.
Use chisel and hammer to remove any pieces of thinset that you are unable to remove with the floor scraper. Place chisel at the seam where the plywood meets the thinset and strike the chisel with the hammer.
Grind off any remaining thinset that was not removed with the other methods. The grinder will create large amounts of dust and should be used as a last resort for removing thinset from plywood.
Sand the plywood after all of the thinset has been removed to insure there is a clean wood surface.
Be careful not to damage the plywood when you are removing the thinset. If the plywood is significantly gouged it is possible to repair the surface by using a floor levelling product or if you are reapplying tile to the plywood you can fill the damaged areas with whatever adhesive you are using for your new tile.