After setting tiles, thinset mortar must quickly be removed or it dries into a hard, stubborn substance. Dried thinset is tough to get off of the tops of tiles, because it is so thin and the tile surface is often delicate. Most tilers attempt to remove the thinset as they work or the next day at the most. If you are new to tiling and allowed the thinset to dry on the tiles, you can still remove it, although it may take some labor and set you back on time. After removing the thinset, you can move on and still obtain professional results.
Fill a bucket with warm soapy water.
Dip a sponge into the soapy water. Wring out excess water and scrub the surface of the tiles, removing any thinset not completely attached.
Wipe the tiles dry with a rag. Shake the rag over a garbage bag to remove any pieces of thinset.
Scrub the surface of the tiles with a foam scrubbing sponge that has a textured side. Scrub the tiles well with the textured side of the sponge. The texture removes dried thinset without scraping the tiles.
Position a chisel on the tile surface. Lightly chisel away at stubborn dried thinset, chipping it off the tile surface. Be careful not to scratch the tile.
Remove dried thinset from grout lines if it measures in excess of 40 percent of the tile thickness. Scrape the thinset down with a grout scraper.
Attach a 50-grit sanding disc to a rotary sander and turn it on at the lowest setting. Carefully and gently position the sanding disc on the thinset until it is removed.
Vacuum the tiles. Use a damp sponge to wipe them down. Polish the tiles with a clean dry rag.