The essentials in 30 seconds
Most tile grout is cement-based and porous, so stains soak in; epoxy grout is almost as stain-resistant as the tile itself. For cement grout, the Tile Council of North America recommends an alkaline cleaner rather than an acid, applied, scrubbed, then rinsed and wet-vacuumed so no soap film stays behind. A baking soda paste and a stiff nylon brush handle most dirt. Keep vinegar and other acids off cement grout and off marble, limestone and travertine. For black mold in a shower, fix the moisture, scrub with detergent and water and dry the area. Once clean and dry, seal cement grout with a penetrating sealer.
- Never mix bleach with ammonia, vinegar or other acid cleaners: the mixtures release toxic gases.
- Squeegee the shower and run the fan after every use to keep grout clean longer.
- Crumbling, cracked or missing grout needs replacing, not cleaning.
Why grout gets dirty
Cement grout is a mix of cement, sand and pigment with tiny pores that absorb water and whatever is in it: floor dirt, cooking grease, soap and body oils in the shower. Grout also sits slightly below the tile surface, so mop water carries dirt into the joints and leaves it there as it dries. In a bathroom, soap film and constant moisture give mold a foothold. Three habits are behind a lot of dark grout: mopping with dirty water, cleaners that leave a film, and wet surfaces that never fully dry.
Know your grout and tile before you clean
Check which grout and tile you have before you buy a cleaner. Epoxy grout feels harder and slightly glossy, almost plastic; cement grout looks matte and sandy and darkens when wet. For stone, ask whoever installed it, or test a hidden spot.
| Surface | What works | What to avoid |
|---|---|---|
| Cement grout (sanded or unsanded) | Alkaline or neutral cleaners, baking soda paste, enzyme cleaners, steam | Acids including vinegar, oil- or wax-based cleaners, cleaner left to dry unrinsed |
| Epoxy grout | Neutral cleaner and water; it resists stains almost as well as tile | Heavy scrubbing with abrasives that dull the surface |
| Glazed ceramic and porcelain tile | Often just water; a neutral cleaner for grease | Sealer sprayed over the glaze, which only adds a coating to wear off |
| Marble, limestone, travertine (calcareous stone) | Neutral stone cleaner, stone soap, or mild dish detergent in warm water | Lemon, vinegar and other acids, which dull or etch; abrasive powders and creams |
| Granite, quartzite (siliceous stone) | Neutral cleaner, stone soap, mild dish detergent | Acidic cleaners in general; rust removers and toilet bowl cleaners, which may contain hydrofluoric acid that attacks all stone |
How to clean grout every week
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01
Sweep or vacuum first
Grit in the joints turns to mud as soon as it gets wet.
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02
Use clean water and a neutral cleaner
Change the mop water often. A dirty mop simply refills the grout lines.
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03
Rinse
Go over the floor with clear water so no cleaner film remains to catch new dirt.
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04
Dry
Wipe dry or let the room air out with a window open or the fan on.
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05
In the shower, squeegee
A squeegee after each shower keeps soap scum and moisture off tile and grout.
How to deep clean grout, step by step
This is the baking soda method, a homemade (DIY) grout cleaner that is safe on cement and epoxy grout with glazed tile, porcelain and most stone.
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01
Vacuum the joints
Use a crevice tool to lift loose grit.
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02
Mix a paste
Baking soda with just enough water to spread like toothpaste.
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03
Work it into the grout
Spread it along a few feet of joints and leave it for a few minutes.
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04
Scrub
Use a stiff nylon grout brush or an old toothbrush along each line. Skip metal brushes and scouring pads, which scratch glazes and can wear down grout.
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Rinse and extract
TCNA's preferred approach is to apply the cleaner, vacuum up the dirty water with a wet-dry vacuum, then rinse with clean water and vacuum again. A sponge and buckets of clean water work too; change the water often.
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Repeat for stubborn lines
An alkaline or enzyme tile-and-grout cleaner from a hardware store takes over where baking soda stops. Follow the label dilution and rinse well.
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07
Try steam last
TCNA notes that pressurized steam can lift some stains that cleaners leave behind.
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Let it dry fully
Let the grout dry completely before you judge the color or apply sealer.
Baking soda and vinegar: skip the fizz
The popular trick of spraying vinegar over baking soda looks impressive, but the fizz is the acid and the alkali cancelling each other out. TCNA also points out that vinegar reacts with cement grout in much the same way it reacts with baking soda, and that grout manufacturers advise against acids because they attack the cement and can strip color. On stone, acids etch. Baking soda paste on its own, scrubbed and rinsed, does the job without that risk.
Stains that need more
Acid cleaners are sometimes used on tough stains or white efflorescence, but TCNA treats them as a last resort that needs great care, often by a professional; strong acids cannot go over acrylic sealers either. Grease stains respond better to an alkaline degreaser, rinsed thoroughly.
Black mold (mould) in shower grout: how to clean grout that has turned black
Black or gray spots in shower grout, especially in corners and the lowest rows, are usually mold growing on soap residue in a space that stays damp. EPA's mold guidance starts with the moisture:
- Ventilate every shower: run the bathroom fan or open a window, and keep indoor humidity below 60 %, ideally 30 to 50 %. A dehumidifier helps in rooms without a fan.
- Scrub hard surfaces with detergent and water, then dry completely. EPA does not recommend bleach as a routine part of mold cleanup.
- If you choose bleach for nonporous surfaces, CDC's dilution for mold is 1 cup of bleach in 1 gallon of water: wash, scrub with a stiff brush, rinse with clean water and let it air dry. Use it on its own, with a window open, and keep it off colored grout you care about.
- On natural stone, the Natural Stone Institute suggests a diluted solution of half a cup of ammonia, bleach or hydrogen peroxide per gallon of water for mildew. Pick one, never two.
- Leave caulk alone until it is clean and dry: EPA warns against caulking or painting over moldy surfaces. Moldy silicone at the tub or tray joint is easier to cut out and replace than to clean.
If spots return within days of cleaning, look deeper. Mold under the surface of the grout, behind loose tiles or behind failed caulk usually means water is getting into the wall. Tap the tiles: a hollow sound or a soft wall needs a closer look, and our guides on mold remediation and black mold on walls cover the next steps.
Grout cleaning machines and when to hire a grout cleaning service
You do not need a special machine to clean grout well. The Tile Council of North America (TCNA) says the best way is to apply the cleaner and vacuum up the dirty water with a wet-dry vacuum (a shop vac), then rinse with clean water and vacuum again: this lifts dirt and soap film out of the joint.
| Machine | What it does | When to use it |
|---|---|---|
| Wet-dry vacuum (shop vac) | Pulls dirty water and cleaner out of the joints | Every deep clean: TCNA's preferred method |
| Steam cleaner | Pressurized steam lifts some stains that cleaners leave behind | When conventional cleaners have not worked |
When to hire a professional grout cleaning service
- Stains that need acid or white efflorescence: TCNA advises great care with acids and says it is generally best to use an experienced professional.
- Mold over about 10 square feet, or mold that comes back through new grout: EPA guidance points to professional help.
- Grout that will not come clean, or is cracked or crumbling: an installer can cut it out and regrout, taking care not to loosen the tiles (see regrouting).
Grout sealer: when and how to seal grout
TCNA recommends sealing cement grout, not epoxy grout, and advises against spraying sealer on glazed tile: the glaze cleans more easily and lasts longer than any coating.
| Type | How it works | Pros | Cons |
|---|---|---|---|
| Penetrating sealer | Soaks in and bonds with the grout, repelling water and water-based stains | Longer lasting, vapor permeable, keeps the natural look | Higher price; some versions repel oil-based stains as well |
| Topical sealer | Forms a coating on the grout surface | Repels nearly everything while intact | Wears off with foot traffic, can look plastic, sensitive to water while curing |
How to seal grout:
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01
Deep clean and dry
Seal only grout that is clean and completely dry, or you lock the stain in.
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02
Protect the tile
Apply with a narrow applicator or small brush along the joints and wipe any sealer off glazed tile straight away.
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03
Follow the cure time
Keep the shower or floor dry for as long as the label says.
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Check it with water
Drip water onto the grout now and then. If it beads, the sealer is working; if it darkens and soaks in quickly, it is time to reseal.
On natural stone, the Natural Stone Institute explains that sealers are really impregnators: they slow staining but never make stone stain-proof. Follow the stone supplier's advice on whether and how often to seal.
When to regrout instead of cleaning
Cleaning will not help when grout is:
- Cracked, crumbling or missing, especially in a shower, where gaps let water into the wall.
- Stained deep into the joint after several deep cleans.
- Moldy again within days of a thorough clean.
- Next to loose or hollow-sounding tiles.
TCNA calls regrouting a last resort and stresses two points: cut the old grout out carefully so you do not loosen or chip the tiles, and remove it to a good depth, because new grout generally will not bond over old, contaminated grout. In a shower, renew the silicone at the corners and the tub or tray edge at the same time. If you are rebuilding the whole enclosure, see our walk-in shower guide.
Grout cleaning: frequently asked questions
What is the best homemade grout cleaner?
A paste of baking soda and water, scrubbed in with a nylon brush and rinsed well. Skip vinegar on cement grout: it is an acid that attacks the cement.
What is the best way to clean grout?
A baking soda paste or alkaline grout cleaner, a stiff nylon brush, and a thorough rinse, ideally picked up with a wet-dry vacuum.
Does vinegar damage grout?
Vinegar is an acid, and acids attack cement grout and etch marble and limestone. Use baking soda or an alkaline cleaner instead.
Can I clean grout with baking soda?
Yes. Make a thick paste, leave it a few minutes, scrub with a stiff brush and rinse well.
How do I get black mold out of shower grout?
Fix the moisture, scrub with detergent and water and dry the area. If you use bleach, dilute it and use it on its own with good ventilation.
Can I mix bleach and vinegar to clean grout?
No. Bleach with vinegar or other acids releases chlorine gas, and bleach with ammonia releases chloramine gases.
Do I need to seal grout?
Seal cement grout once it is clean and dry. Epoxy grout and glazed tile do not need sealer.
How do I know when to reseal grout?
Drip water on it. If the water beads, the sealer is working; if the grout darkens quickly, reseal.
When should grout be replaced?
When it is cracked, crumbling, missing, or stained or moldy deep into the joint after repeated cleaning.
Sources
Tile, stone and public health guidance, checked on 27 October 2026.
- Tile Council of North America · Cleaning grout ↗Porous cement grout, alkaline over acid cleaners, vacuum extraction, steam, epoxy grout stain resistance, penetrating and topical sealers, no sealer on glazed tile, regrouting.
- Natural Stone Institute · Cleaning products for natural stone ↗Acids on calcareous stone, hydrofluoric acid in rust removers and toilet cleaners, squeegees, mildew solutions, sealers as impregnators.
- US EPA · A brief guide to mold, moisture and your home ↗Detergent and water on hard surfaces, 10 square feet threshold, N-95 respirator, humidity targets, no caulking over mold, bleach cautions.
- CDC · How to safely clean and sanitize with bleach ↗1 cup per gallon for mold on hard surfaces, ventilation, gloves and eye protection, never mixing bleach with other cleaners.
- Washington State Department of Health · Dangers of mixing bleach with cleaners ↗Ammonia and acid products that react with bleach, chloramine and chlorine gas, symptoms and when to get help.
Grout looking tired?
Try the baking soda method on one square foot first and compare it with the rest of the floor.