How to Regrout Bathroom Tile

Before grinding anything, tap firmly across the tiles with a knuckle or the handle of a screwdriver. A solid 'tock' means the tile is well-bonded; a hollow 'drummy' sound means the tile has separated from the wall and water may have gotten behind it — that's a tear-out job, not a regrout. Also check for tiles that wiggle, cracked tiles, and any black staining seeping out from behind (not just on the grout surface). If the tile is sound and only the grout looks bad, you're good to proceed.

Cover the tub or shower drain with painter's tape so grout chips and dust don't wash into the trap and clog it. Lay a drop cloth or plastic sheeting over the tub floor and any nearby countertop. Put on safety glasses and an N95 dust mask — grinding cementitious grout throws fine silica dust that's genuinely harmful to breathe. Open a window or run the bath fan for ventilation.

Fit your oscillating multi-tool with a carbide grout-removal blade and run it down the center of each grout line, making a shallow scoring pass first, then a second pass to take it down to roughly 1/8 inch deep. Keep the blade centered — riding it against the tile edges chips the glaze. For tight or detailed spots, finish with a manual grout saw. Work in sections and vacuum as you go so you can see the joints.

Run the shop vac along every grout line to pull out the loose grit, then wipe the whole area with a damp sponge to capture the fine dust. The joints must be completely free of dust and loose debris — new grout will not bond to a dusty channel. Let the tile dry fully before grouting; grouting into damp joints throws off the water ratio and weakens the cure.

Choose sanded grout for joints 1/8 inch and wider, unsanded for narrower joints. In a bucket, add the powder to the water (not the other way around) per the bag ratio, and mix with a margin trowel or drill paddle until it's smooth and holds its shape like peanut butter — not soupy. Let it 'slake' (rest) for 5-10 minutes, then remix briefly. Only mix what you can use in about 30 minutes before it starts setting in the bucket.

Scoop grout onto the rubber float and spread it across the tile holding the float at a 45-degree angle to the joints. Work diagonally across the lines (not parallel to them) so the float packs grout fully into each joint instead of dragging it back out. Make passes from several directions to fill every line completely with no gaps or air pockets. Then hold the float at a steeper angle and scrape the excess off the tile faces.

After the grout has firmed up for about 15-20 minutes (it should resist a light fingernail press), wipe the tile faces with a damp — not soaking — sponge using light pressure. Rinse the sponge in clean water constantly and wring it out well; a too-wet sponge pulls grout out of the joints and weakens them. Use rounded edge passes to shape each joint into a smooth, slightly concave line. Don't scrub.

As the grout dries, a powdery film called haze appears on the tile. Once the joints are firm (an hour or two), buff the haze off the tile faces with a dry lint-free cloth; for stubborn film, use a 1:1 vinegar-water mix or commercial haze remover. Then run 100% silicone caulk — not grout — into every inside corner and the joint where tile meets the tub. These flexing joints crack if grouted; caulk stays flexible.