After new tile installation, it is necessary to fill the spaces between the tiles with grout to finish off the look. Before the grout application, you must clean the tiles and grout lines to get proper adhesion of the grout. If there is dust in the spaces between the tiles, the new grout may not set correctly. Cleaning the tiles before replacing old grout is even more important because of the dust and grout fragments that are left over from removing the old grout.
Scrape out all the old grout if you are regrouting existing tile. Use a grout scraping tool or anything with a hard, sharp blade to scrape out all the old grout. Use more than one tool, such as a grout saw and a utility knife, to get all fragments of old grout from between the tiles. Spend a lot of time and patience with this step. Do not scratch the surface of the tiles. If this is a new tile installation, let the tile adhesive dry completely before cleaning the tile before grouting.
Vacuum the tiles to remove all the dust and old grout fragments from between old tiles. With new tile installations, vacuuming removes any construction debris and dust from the tile saw that may have been used in the area.
Combine 1 part water and 1 part vinegar in a bucket. Dip a sponge into the mixture and squeeze out all the liquid so the sponge is only damp. Wipe the tiles, turning the sponge often and rewetting it. Let the tile dry.
Rinse out the sponge and wipe the tile a second time, using only warm water. Let the tile dry completely. Now the tile is ready for you to apply the grout.