Prep first
Before you start
- Work out the cause first: where the mark sits, its smell and feel, and how it appeared all point to the right treatment.
- Until you know whether the grout is cement or epoxy, stick to water and a nylon pad.
- Dry soot and mildew come off best when brushed or vacuumed before anything gets wet.
Black stains on grout are usually mildew or soot, though manganese from well water and greasy residue can look just as dark. In Portland cement grout a stain can become part of the grout itself, so a set-in mark may fade rather than fully lift. Epoxy grout can always be cleaned back to its original color, so the type of grout you have decides how far you can take it.
To remove black stains from grout, reach for an enzyme grout cleaner before anything harsh, since it's gentler. Work the brush into the black stains in shower grout, and rinse well before the cleaner dries. If the mark is still there after two rounds, call a tile professional rather than scrubbing harder.
Before you start
What grout can take
Safe to use4
- Water
- Hot water
- Enzyme cleaners
- Heat, once the stain is out
Use with care5
- Soaking
- Chlorine bleach
- Solvents (alcohol, spot removers)
- Acids (vinegar, lemon)
- Scrubbing and abrasives
8 items
What you'll need
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- Soft brush or vacuumClears dry soot and loose mildew before any water touches it. (opens Amazon)
- White nylon scrub padThe recommended tool for grout, and gentle enough for regular scrubbing. (opens Amazon)
- Old toothbrushGets the scrubbing down into the grout lines.
- Warm water and clean hot waterWarm water loosens the mark, and clean hot water makes a good final rinse.
- Enzyme cleanerFor marks that stay after scrubbing; it's one of the specialty cleaners made for grout. (opens Amazon)
- Towels and good ventilationDry the grout so you can check the result, and keep fumes moving. Keep open flames away from flammable cleaning solutions.
- Distilled white vinegar (opens Amazon)
- Grout cleaner (opens Amazon)
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6 steps
Step by step
Step 1 of 6
Brush off dry soot and mildew
Start by brushing or vacuuming away any dry soot and loose mildew, since it comes off far more easily before it gets wet. If the mildew is on the grout, do the brushing outdoors so the loose dust doesn't settle back into the room.
Step 2 of 6
Scrub or wash the grout first
Wet the grout with warm water and scrub the black lines with a white nylon pad. On epoxy grout only, you can use a mildew wash of 1/2 cup white vinegar, 1/4 cup Washing (sal) Soda and 1 gallon warm water instead, then rinse it out thoroughly.
Tip. Use white vinegar only; colored vinegar can leave a stain.
Careful. Test any cleaner on a hidden spot first.
Step 3 of 6
Scrub the lines with a toothbrush
Dip an old toothbrush in warm water and work it along the grout lines, pressing the bristles into the joints. Then rinse the area thoroughly with clean water.
Careful. Harsh abrasives can damage grout, so stick to nylon brushes and pads.
Step 4 of 6
Let an enzyme cleaner work
If the marks are still dark, apply an enzyme cleaner, which is one of the specialty cleaners made for grout. Let it dwell for several minutes, since some heavy-duty grout cleaners can be left up to 10 minutes.
Careful. Don't let cleaning solution dry on the surface.
Step 5 of 6
Rinse with clean hot water
Once the enzyme cleaner has worked, rinse the grout with clean hot water. Hot water is a good final pass for grout, and it helps clear loosened dirt out of the lines.
Step 6 of 6
Check for residue and dry
Rinse once more with clean water, then wipe the grout dry. Look at it in good light, and if the area feels slick or looks cloudy, rinse it again before you decide the mark is gone.
Careful. Even good alkaline cleaners leave a sticky soap film if they aren't rinsed.
If you'd rather buy than mix
Best products for black stains on grout
Choose an enzyme cleaner or a grout cleaner made for your grout type, and read the packaging to confirm it suits cement or epoxy.
Zep Grout Cleaner & Brightener
How we picked these: each product is made for this type of stain, its maker doesn't warn against using it on grout, and its directions fit the steps above.
Finished the steps? How does it look?
Nice work. Let it dry completely and check it again in good light. Here is what done looks like:
How to tell it's really gone →A faint mark usually needs one more round, not a stronger product.
Heavy buildup usually takes more than one round.
Heavy or long-standing buildup →When to call a professional →How to tell it's working
Clean grout looks even in color once it's fully dry, with no dark shadows left in the joints. The rinse is complete when the surface no longer feels slick, and any mark that remains after that is probably a set-in or damage case.
What changes for yours
Adjust for your grout
Shower grout
Shower grout stays damp, so black marks there are usually mildew, and they return quickly if the grout stays wet. The same brushing and warm water scrub applies, but let the grout dry fully before you judge the result.
After your rinse, dry the walls and grout with a towel and leave the bathroom ventilated for a while. If the marks come back quickly, the grout probably needs the set-in options below rather than another round of scrubbing.
Epoxy grout
Epoxy grout is the one type that can take the mildew wash from the second step, along with the hot water rinse. Use the wash only once you've confirmed the grout is epoxy.
Everything else in the steps stays the same. If the mark is still there after drying, the set-in options apply, and a bleaching cleanser for tough soil is only an option on epoxy.
Sealed cement grout
Cement grout changes the plan more than anything else. Skip the mildew wash entirely and keep to warm water, the nylon pad, the toothbrush and an enzyme cleaner.
If you're not sure whether the grout is sealed, treat it as sealed and use only those tools. When you do reach for a cleaner, choose one made for grout rather than a general-purpose product.
Soot and greasy residue
Soot is easiest to deal with dry, so brush or vacuum as much of it away as you can before any water goes near the grout. Greasy residue usually needs the full scrub and the enzyme step, so give it the time the steps allow.
Soot and grease can share the same grout lines, so don't skip the toothbrush pass. Check the grout after each rinse before you decide the job is finished.
Manganese from well water
Black marks from well water look like mildew, but they keep returning until the water source is dealt with. Use the same scrub and rinse, and judge the result by whether the mark comes back.
Expect the set-in notes to describe the realistic result for these marks. One cleaning may not end the problem, so plan to check the grout again after a few uses.
Heavy or long-standing buildup
Old black marks are the hardest to shift, because they've had time to soak into the grout. On cement grout, a stain can become part of the grout itself, and some black marks are damage rather than dirt, which cleaning can't reverse.
If a stain has dried, repeat the nylon pad scrub and the toothbrush scrub before trying anything else. Pressurized steam can clean stains that don't respond to conventional cleaners, and a commercial mildew stain remover can be used following the package directions when the other steps fail. Chlorine bleach is an option only on epoxy grout, and only after you've ruled out manganese and iron; use it last, after everything is rinsed out.
Epoxy grout can usually be cleaned back to its original color, but cement grout may keep some discoloration after heavy staining. Manganese from well water keeps coming back until the source is dealt with, so a clean result may not last there.
Vinegar, baking soda, peroxide and more
Do home remedies work on black stains on grout?
Plenty of household remedies get suggested for black grout, but most are written for fabric or other surfaces. Only a few are worth using, and the others should be left alone.
Works1Skip5
Chemical safety
Never mix these
Some products in this guide react dangerously with each other. Use them one at a time and rinse with water in between.
Enzyme cleaner + Vinegar
Some enzyme and pet stain removers' makers say not to mix them with vinegar or acidic cleaners, or with other household chemicals.
If they mix by accident: Don't use the mixture; ventilate the room and avoid breathing fumes or touching it; call Poison Control at 1-800-222-1222 for disposal advice or if anyone feels unwell.
What makes it worse
Mistakes to avoid
Don't use chlorine bleach on manganese or iron stains.
Bleach intensifies those stains, so a dark mark from well water can get darker. If you haven't ruled out manganese or iron, leave the bleach on the shelf.
Don't mix bleach with vinegar or ammonia.
Never mix bleach with acids such as vinegar, and never add ammonia or ammonia-containing detergents to it, since that forms a toxic gas. Rinse thoroughly between any two products.
Don't paint over mildew.
Paint over mildew and it keeps growing underneath the coat. Clean the grout first and let it dry completely before you think about any coating.
Don't use vinegar or ammonia on sealed cement grout.
Acids etch cement-based grout, and general bathroom cleaners break down the sealer that protects it. Bleach-containing cleaners are off limits here too.
Don't use oil- or wax-based cleaners.
They leave a film in the grout that makes the surface harder to clean. Stick to water-based cleaners on grout.
Don't use strong acid solutions on grout.
Strong acid makes grout lose its color or turn powdery or sandy, and it dulls glazed tile around it.
When to call a professional
Acid cleaning needs extreme care, so leave it to a professional. For deeply set or especially stubborn grout stains, contact the grout manufacturer's technical support team.
Questions
Can black grout be cleaned without harsh chemicals?
Usually, yes. Brushing and warm water with a nylon pad handle many marks, and an enzyme cleaner is the next step if they don't lift.
What usually causes black spots in shower grout?
Mildew is the most likely cause in a shower, since the grout stays damp. Manganese from well water, soot and greasy residue can cause the same look, so check where and how the mark appeared.
Why do black marks come back?
Mildew returns when the grout stays wet, so drying the area matters as much as cleaning it. Manganese from well water also keeps coming back until the source is dealt with.
How long should a grout cleaner sit?
Several minutes is typical, and some heavy-duty grout cleaners can be left up to 10 minutes. Keep an eye on the time and rinse it off in good time.
Can steam remove black stains from grout?
Pressurized steam can clean stains that don't respond to conventional cleaners, so it's a reasonable next step. It's a set-in option, so try the steps above first.
What if the black mark is damage in the grout?
Some black marks are damage rather than dirt, and cleaning can't reverse that. If a mark is still there after the steps and set-in options, it's probably damage and won't come out completely.
Black Stains on other materials
Other stains on grout
Start from the bigger picture
How we know this
Every method, amount and warning here comes from university extension services, industry bodies and product makers. We read them, check every step for unsafe combinations and changed amounts, and write it up so you can follow it.