Bathroom tiles with bad-looking grout can ruin a good-looking tile job. Excess grout makes the grout joints look uneven and large. When bathroom tile still has a grout film on its the surface, a grout haze will form and the tile will always look dull and dirty. Regrouting tile without first removing the old grout, the worst possible way to renew grout, will eventually lead to cracked, discoloured and flaking grout. The proper way to renew a bathroom's grout involves removing the old grout and polishing the tile before regrouting.
Cut the centre of the grout joint to the backerboard, for wall tile, or the subfloor, using a handheld grout saw on grout joints at least 1/4 inch wide and a utility knife on thinner grout joints. A grout saw has a thin, diamond-tipped blade that will turn grout to a fine powder.
Cut the grout away from the tiles' edges with a utility knife. Use the utility knife's blade to pry the grout from the edge and into the cut-out section. With the grout's centre removed, grout that sticks to the tiles' edges will break free easily.
Remove the debris from the grout joints with a vacuum.
Pour vinegar on the tiles to remove grout haze. Vinegar, a mild, non-staining acid, will remove thin layers of grout and grout haze. Let the vinegar set for five minutes.
Scrub the surface with a nylon brush. Tile with leftover grout or haze has more friction than tile with a clean surface. Scrub one tile at a time, but complete the entire floor.
Soak up the vinegar from the grout joints with a sponge. Rinse the sponge in a bucket of clean water, then wash the tiles with a clean sponge. If the sponge slides easily over the surface and hits a spot that seems to grip the sponge, scrub that spot with the nylon brush. Allow the surface and the water and vinegar in the grout joints to dry.
Polish the tile with a clean, dry rag.