Things You'll Need
3-gallon plastic bucket
1-gallon cold water
1 cup phosphoric acid
Paint stir stick
Natural-bristle scrub brush
Clean terry cloth towel
Ceramic tiles are recognized for their durability, resistance and numerous designs. Tiles are adhered and sealed with cement grout during installation to provide stability and seal joints. Failure to properly clean tile surfaces after grouting causes them to become marred with unsightly grout residue and haze. The longer grout remains on surfaces, the stronger it becomes and more difficult it is to remove. Acid-washing is a last-resort option for removing hard or cured grout from ceramic tiles.
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Fill a 3-gallon plastic bucket with 1 gallon of cold water. Slowly pour 1 cup of phosphoric acid into the water. Thoroughly mix the acid solution with a paint stir stick.
Fill a spray bottle with cold water. Spray water liberally over the dried grout. Saturate the tile with water.
Soak a clean sponge in the acid solution. Wipe dried grout with the soaked sponge. Keep the acid solution on the tile for five minutes to dissolve the dried grout.
Scrub the affected tile diagonally with a natural-bristle scrub brush. Remove as much grout as possible.
Spray water generously onto the tile to rinse away the acid solution. Do not allow the acid solution to dry on the tile.
Extract the dirty water and loosened grout debris from the tile, using a wet vacuum. Operate the wet vacuum according to the manufacturer's directions.
Continue washing the tile with the acid solution if traces of dry grout remain, using the same process.
Dry the tile with a clean terry cloth towel. Repeat the acid-washing process on any remaining tiles affected with dry grout.
Put on vinyl-coated coveralls, safety glasses, heavy-duty rubber gloves and a NIOSH (National Institute for Occupational Safety and Health) respirator for protection against the acid. Open all windows in the room to provide adequate air circulation. Set up portable fans if no windows are available.
Pour the acid solution directly onto extremely stubborn grout residue.
Allow new grout to cure for two weeks before acid-washing; acids can damage fresh grouts.
Do not use muriatic acid on tile grout; hydrochloric acids can damage tiles, grout and other materials.
Test the acid solution on an inconspicuous area of a tile to ensure no damage or discoloration occurs.
Follow the phosphoric manufacturer’s directions on the product label to prevent health hazards.