How to clean grout: from a quick scrub to oxygen bleach

Step by step: how to clean grout

Safety first. Never mix chlorine bleach with vinegar, ammonia or other cleaners: the fumes are toxic. Open a window or run the bath fan, wear gloves, and keep acids such as vinegar off natural stone tile.

1. 1

   Find out what you are cleaning

   Check whether the tile is ceramic, porcelain or natural stone, and whether the grout is ordinary cement grout or epoxy. Stone and colored grout need gentler, pH-neutral products. If you are not sure, test every cleaner on a hidden joint first and wait a few minutes to see whether the color changes.

2. 2

   Sweep or rinse off loose dirt

   Vacuum or sweep a floor, or rinse shower walls with warm water. Grit left on the surface turns into mud when you scrub and gets pushed deeper into the grout. Starting with clean tile means the brush works on the stain, not on loose dirt.

3. 3

   Scrub with warm water first

   Wet a section of about 3 feet by 3 feet and scrub along each grout line with a stiff nylon brush, using short back-and-forth strokes. Light surface grime often lifts with water alone. Wipe the dirty water up with a cloth before it dries back into the joints.

4. 4

   Work in a baking soda paste

   Mix about 1/2 cup of baking soda with enough water to make a thick paste and press it into the dirty joints with the brush or a gloved finger. Leave it for 5 to 10 minutes, then scrub. The mild grit lifts embedded dirt without scratching glazed tile.

5. 5

   Soak stained grout with oxygen bleach

   For gray or stained cement grout, dissolve oxygen bleach powder in warm water at the strength on the label and pour or spray it onto the grout lines. Keep the joints wet for 10 to 15 minutes; you will see it fizz gently as it works. Scrub again, and the original grout color should start to show.

6. 6

   Treat mold spots on white grout

   If black or pink spots remain on white grout, use a diluted chlorine bleach solution of about 1/3 cup bleach per gallon of water, as Clorox directs, and keep the surface wet for 10 minutes. Rinse thoroughly. Do not use chlorine bleach on colored grout, which it can lighten unevenly.

7. 7

   Rinse and dry the floor or walls

   Rinse with clean water two or three times, changing the water as it gets cloudy, so no cleaner residue is left to attract new dirt. Wipe or mop the tile dry. Grout looks darker while wet, so judge the result only after it has dried for a few hours.

8. 8

   Seal the grout once it is fully dry

   Let cement grout dry for at least 24 hours, or as long as the sealer label says, then brush a penetrating sealer onto the joints and wipe any excess off the tile within a few minutes. Sealed grout soaks up less water and dirt, so the next clean is a quick wipe rather than a scrub.

Which grout cleaner works best?

The best grout cleaner is the mildest one that works: water and a brush for light grime, baking soda for embedded dirt, oxygen bleach for gray stains, and diluted chlorine bleach only for mold on white grout.

Clorox’s grout instructions call for 1/3 cup of bleach per gallon of water, mixed fresh, with gloves on and the room ventilated, and warn never to mix bleach with vinegar or ammonia.

How to clean cement, epoxy and premixed grout

Cement grout is porous and stains, so it takes the stronger methods above. Epoxy and most premixed grouts barely absorb anything, so they clean up with a neutral cleaner and are easily damaged by harsh ones. If you do not know which you have, look for leftover bags or buckets from the install, or ask the installer.

Laticrete’s cement grout care tips recommend a clear, pH-neutral cleaner for everyday cleaning, an alkaline cleaner for grease, and products made for mold, soap scum or hard water when those are the problem. It also points out that no cement grout is self-cleaning or completely stain-resistant, so wipe spills quickly. Its method for stubborn spots is worth copying: dampen the grout with water first, apply the cleaner, let it sit for 3 to 4 minutes, then scrub. Pre-wetting keeps the cleaner on the surface instead of soaking straight into dry grout. Before any new product, test it on a small hidden joint and let it dry.

For epoxy and other non-cement grouts, Mapei’s maintenance bulletin warns that strong alkaline, acidic, abrasive and ammonia-based cleaners can damage grout and greatly reduce how well a sealer repels stains. It recommends a mild, neutral-pH cleaner, regular damp-mopping and a scrub about once a month. White crust on grout is usually mineral scale rather than dirt; see our guide on removing hard water stains.

How to clean new grout and remove grout haze

Give new grout time to cure before you scrub it, and treat the cloudy film on the tiles, called grout haze, with a product matched to the grout and its age.

When you can start cleaning

Mapei’s grout troubleshooting guide says to wait 72 hours before routine cleaning of new grout, and lists cleaning too soon as a common cause of problems. Some products need longer, so check the bag or bucket. Sealing comes after that: Custom Building Products says to apply sealer 48 to 72 hours after grouting, and Mapei says to wait at least 72 hours before sealing a premixed grout.

Removing cement grout haze

• In the first 10 days, a grout haze clean-up product made for new installs and a nylon scrub pad usually lift light haze.
• After 10 days, cement haze generally needs an acidic haze remover. The label for Aqua Mix Cement Grout Haze Remover says to let the grout cure at least 10 days, pre-wet the tile, use 1 part cleaner to 3 parts water for light haze (up to full strength for heavy haze), scrub small areas with a white nylon brush, and flush with water right after brushing. Wear chemical-resistant gloves.
• The same label warns that acids can etch or discolor marble, limestone, travertine and some other stones, and that it is not for epoxy or premixed grout haze. Those need a non-cement haze remover.

Epoxy haze is the hardest to shift. Mapei notes that the longer the residue cures on the tile, the harder it is to remove, so deal with it as early as the grout maker allows.

Why floor grout turns dark, and how to stop it

Floor grout often darkens because dirty mop water settles into it, not because of mold. Every time you mop with a bucket that has gone gray, you push that dirt into the lowest part of the floor: the joints.

• Vacuum or sweep before you mop, so you are not making mud.
• Mop with a pH-neutral floor cleaner and change the water as soon as it looks cloudy.
• Use a two-bucket method or a spray mop with a clean pad, so dirty water never goes back on the floor.
• Finish with a plain-water rinse in kitchens, where grease builds up in the joints.
• Put mats at outside doors to catch grit before it reaches the tile.

Shower grout is a different problem, driven by soap scum and moisture. Our guides on shower tiles and shower mold cover it.

What not to use on grout

Skip acids, wire brushes and full-strength bleach. Each one either damages the grout or wears it away faster than dirt ever would.

• Vinegar and other acids slowly dissolve cement grout, and repeated use leaves the joints rough and porous so they stain faster.
• On marble, travertine and limestone, acids also etch the stone itself. The Natural Stone Institute recommends a neutral cleaner, stone soap or mild dish soap for these stones. See our travertine guide for stone floors and showers.
• Wire brushes and metal scrapers gouge grout and scratch glazed tile edges.
• Undiluted bleach can discolor grout and is harsher than you need; a measured dilution does the job.

How to keep grout clean longer

Keep grout dry and sealed. Moisture feeds mold, and unsealed grout drinks in dirty mop water and soap scum.

Run the bathroom fan during showers and for a while after, and squeegee the walls. The EPA’s guide to mold and moisture stresses that the key to mold control is moisture control, and that a fan or an open window helps in bathrooms. To check whether your grout needs sealing, drip a little water on a joint: if it darkens within a few minutes, the grout is absorbing water and it is time to reseal. Epoxy grout is not porous and does not need sealing.

For a full shower routine, pair this with our guide on how to clean shower tiles.

When grout needs repair instead of cleaning

If grout is cracked, crumbling, missing in places, or still stained after oxygen bleach and a second scrub, cleaning will not fix it. Cracked grout lets water behind the tile, which leads to mold you cannot reach and can damage the wall or subfloor.

Small areas can be raked out and regrouted by a careful DIYer. A grout colorant can even out sound but stained joints. Widespread cracks, loose tiles or a soft spot in a shower wall are a job for a tile professional.

Mistakes to avoid

• Cleaning grout with vinegar every week, which slowly eats away cement grout.
• Using chlorine bleach on colored grout and leaving pale, blotchy joints.
• Mixing bleach with vinegar or an ammonia cleaner to make it "stronger".
• Skipping the rinse, so cleaner residue dries in the joints and grabs dirt.
• Sealing grout while it is still damp, which traps moisture under the sealer.
• Scrubbing with a wire brush that scratches tile and gouges the grout.
• Scrubbing or sealing new grout before it has cured; wait at least 72 hours unless the label says otherwise.
• Using an acid cement haze remover on epoxy grout, premixed grout or natural stone.
• Mopping with the same gray water from start to finish, which settles dirt into the joints.