How to Clean, Repair and Seal Tile Grout

Dirty, stained or crumbling grout can make a perfectly good tile floor or shower look tired. Before you price out new tile, know that most grout problems can be fixed with a deep cleaning, some spot repairs and a fresh coat of sealer. It’s slow, patient work, but the tools are inexpensive and the difference is dramatic. Just as important, keeping grout sound and sealed in a shower helps keep water where it belongs instead of soaking into the wall behind the tile.

Difficulty: Beginner to intermediate · Time: 2–6 hours for a bathroom, plus curing time

Tools and materials

• Stiff nylon grout brush (avoid wire brushes, which scratch tile)
• pH-neutral tile and grout cleaner; oxygen bleach powder for stained grout
• Spray bottle, buckets and microfiber towels
• Manual grout saw or carbide grout scraper (an oscillating tool with a grout blade speeds up bigger jobs)
• Shop vacuum
• Grout: sanded, unsanded or a premixed urethane/acrylic grout, color-matched
• Rubber grout float, grout sponge and a margin trowel
• Penetrating grout sealer and a small brush or applicator bottle
• Rubber gloves, safety glasses and a dust mask

Step 1: Deep clean

1. Start gentle. Spray the grout with a pH-neutral tile cleaner, let it sit a few minutes and scrub along each joint with the nylon brush. Wipe up the dirty water with a damp towel before it dries back into the grout.
2. Use oxygen bleach for stains. Mix powdered oxygen bleach with warm water per the label, apply it to the joints, let it work 10–15 minutes, then scrub and rinse well.
3. Be careful with acids and harsh chemicals. Vinegar and acidic cleaners can etch natural stone like marble and travertine and slowly eat away cement grout. Never mix bleach with ammonia or acid-based cleaners; the fumes are toxic. Keep the room ventilated with the exhaust fan running.
4. Rinse and dry. Rinse with clean water and let everything dry completely, at least 24 hours for a shower, before deciding what needs repair or sealing.

Step 2: Inspect and decide what to repair

Once it’s clean and dry, look closely. Small hairline cracks, missing chunks, sandy grout that crumbles when you scratch it with a key, or gaps along the edges of tiles all need repair. If grout is cracked in a line along the floor, check whether the tiles sound hollow when you tap them with a screwdriver handle. Hollow tiles and widespread cracking often mean the floor is flexing or the tile has lost its bond, and new grout alone won’t last.

Step 3: Remove damaged grout

1. Cut out the bad grout. Run a grout saw back and forth in the joint, keeping the blade centered so it doesn’t chip the tile edges. Remove grout to at least two-thirds of the tile depth, or about 1/8 inch for thin joints.
2. Go slow with power tools. An oscillating tool works fast but can chip glazed tile in a split second. Keep it centered and use light pressure.
3. Vacuum the joints clean. Then wipe with a damp sponge to remove dust so the new grout bonds.

Step 4: Choose the right grout

• Unsanded grout is for joints 1/8 inch wide or narrower, and for polished stone or glass tile that sand could scratch.
• Sanded grout is for joints wider than 1/8 inch. The sand adds strength and keeps it from shrinking and cracking in wider joints.
• Premixed urethane or acrylic grouts are stain-resistant, flexible and often don’t need sealing. They cost more but are a good choice for spot repairs because they come ready to use.
• Epoxy grout is nearly stain-proof and waterproof but sets fast and is tricky to work with. It’s best left to experienced installers.

Color matching old grout is hard, because grout darkens with age. Take a small piece of the old grout to the store and compare it to the color samples while it is clean and dry. For large repairs, regrouting a whole wall or floor section gives a more even look than patching.

Step 5: Regrout

1. Mix in small batches. For powdered grout, mix to a peanut-butter consistency and let it slake (rest) for 5–10 minutes, then remix. Don’t add water after slaking.
2. Pack the joints. Hold the rubber float at about 45 degrees and push grout diagonally across the joints so it fills them completely.
3. Remove the excess. Scrape off the surplus with the edge of the float held nearly upright, again moving diagonally so you don’t pull grout out of the joints.
4. Sponge it clean. After 15–30 minutes, when the grout is firm, wipe with a barely damp sponge in light, circular passes. Rinse the sponge often. Too much water weakens grout and lightens the color.
5. Buff off the haze. Once dry, buff the leftover film off the tile faces with a dry microfiber cloth.
6. Let it cure. Keep the shower dry for at least 72 hours, or as long as the bag recommends.

Step 6: Seal it

Cement grout is porous and absorbs water, soap and stains. A penetrating sealer soaks in and helps it shed moisture. Wait until new grout has fully cured; many manufacturers say 48–72 hours, but check the label, as some recommend longer. Apply sealer to the joints with a small brush or applicator tip, let it penetrate for the time listed, then wipe any excess off the tile before it dries into a sticky film. Two light coats usually beat one heavy one. Reseal showers about once a year and floors every one to three years. A simple test: sprinkle water on the grout. If it beads up, the sealer is working. If it darkens quickly, it’s time to reseal.

Mistakes to avoid

• Grouting the corners and change-of-plane joints. Where a tub meets tile, wall meets floor, or two walls meet, use a color-matched 100% silicone caulk instead of grout. Those joints move, and grout will crack there.
• Using too much water when sponging.
• Sealing grout that is still damp. It traps moisture and can leave a cloudy finish.
• Scrubbing stone with acidic cleaners.

When to call a pro

New grout won’t fix tiles that are loose, cracked or hollow-sounding, and it won’t fix a shower that is already leaking behind the tile. Warning signs include soft or discolored drywall outside the shower, peeling paint on the ceiling below the bathroom, a musty smell that won’t clear, or grout that keeps cracking in the same spots. Those usually point to a failed waterproofing layer or a flexing subfloor, and the right fix is opening it up and rebuilding it properly. RossBuilt builds tile showers and remodels bathrooms through our kitchen and bath services, and we install tile floors as part of our flooring services.

Rather have it done for you? RossBuilt Construction serves the St. Louis metro. Request a free estimate or call 636-380-2574.