If you want to know how to clean grout without wrecking it, the short answer is: start mild, and only climb as far as the dirt forces you to. Most grout is cement with pigment in it, and cement is porous. It drinks up soap scum, body oil, grease and dirty mop water, which is why the lines darken even when the tiles look fine. Most of that dirt sits near the top, not all the way through. Reaching for the strongest chemical first is the usual mistake — the products that strip grout fastest often destroy it slowly.

The approach below is a ladder. Start at the mildest rung, give it a fair dwell time, and only climb if the dirt is still there. Every rung assumes ceramic or porcelain tile with cement-based grout, which covers most homes. Epoxy or pre-mixed grout is less porous and usually needs nothing stronger than the first two rungs.

Read this before you mix anything

  • Never mix bleach with vinegar, any acid, or ammonia. Those combinations release toxic gases. Use one cleaner at a time, and rinse thoroughly with plain water before trying a different one.
  • Open a window or run the exhaust fan, and wear gloves for anything stronger than dish soap.
  • Test every method in a hidden spot first — behind the toilet, inside a closet, under the bath mat. Wait for it to dry before judging, because wet grout always looks darker than it really is.
  • Natural stone changes the rules. Marble, travertine, limestone and slate are etched by acids, including vinegar and acidic brighteners. If your tile is stone, stay with a pH-neutral cleaner made for stone and skip every acid step. Grout manufacturer MAPEI is blunt about this in its tile and grout care guidance: acidic solutions should never be used for routine cleaning of tile and grout.

What you need

Prices are approximate US retail prices as of November 2026.

  • A stiff nylon grout brush or old toothbrush ($3–$8)
  • Baking soda (about $1–$2 a box) and 3% hydrogen peroxide (about $1)
  • Powdered oxygen bleach — sodium percarbonate, or an “oxy” stain remover ($10–$15 a tub)
  • A pH-neutral tile and grout cleaner for maintenance (about $8–$12)
  • A bucket, spray bottle, sponges or microfibre cloths, and a towel
  • Optional, for later rungs: a commercial grout cleaner ($8–$15) and a penetrating grout sealer ($15–$30)

Step zero: work out what the dirt actually is

Thirty seconds of looking saves a lot of scrubbing, because the three usual problems respond to different things.

  • Grey or brown, worst in walkways and around the hob: ground-in dirt, grease and soap film. The ladder below is built for this.
  • Black, green or pink spots in the shower, worst in corners and along the bath edge: mould or mildew in a damp film. That needs the mould section further down, not just a stronger cleaner.
  • White, chalky crust that feels rough: mineral deposits or efflorescence, salts wicking out of cement grout. This is the one case where a brief, targeted acidic cleaner can help — on ceramic or porcelain only, never as a routine.

Whatever it is, start dry. Sweep or vacuum first so you are not grinding grit into the grout, then wet the area with warm water so the cleaner does not soak straight in.

Level 1: Hot water, detergent and a brush

For light dinginess, this is genuinely enough. Mix a few drops of washing-up liquid in hot water, work it along the lines in short strokes, and rinse with clean water. Change dirty rinse water as you go; mopping grout with grey water just puts the dirt back. Dry with a towel so you can see the true colour, and only move up if the lines are still dark.

Level 2: Baking soda and hydrogen peroxide paste

This is the workhorse for soap scum and general yellowing. Stir about ½ cup of baking soda with ¼ cup of 3% hydrogen peroxide and a teaspoon of washing-up liquid into a paste the texture of toothpaste. Spread it along the lines with a gloved finger, an old knife or the brush, and let it sit for 10 to 15 minutes. Scrub along each line, rinse well, and dry.

Two cautions. Peroxide is a mild bleach, so on coloured grout it can lighten the pigment — this is what your test spot is for. And do not spray vinegar over this paste to make it fizz: acid and peroxide neutralise each other, so the fizz is both cleaners cancelling out, and the vinegar adds acid damage on top.

Level 3: An oxygen bleach soak

For large floor areas or uniformly grey grout, powdered oxygen bleach does more work with less scrubbing. It is a different chemical from chlorine bleach: sodium percarbonate releases hydrogen peroxide when it dissolves, and it is generally colour-safe, though the test spot rule still applies.

Dissolve the powder in warm-to-hot water at the strength on the tub — the label ratio governs, because products vary. Pour or sponge the solution along the lines so they stay flooded, and let it dwell for 20 to 30 minutes, misting if it starts to dry out. A cleaner that has dried has stopped working. Scrub, then rinse twice. On wall tiles, use a thicker paste so it clings.

Level 4: Commercial grout cleaners

Purpose-made cleaners come in two families, and the label matters more than the brand.

  • Alkaline heavy-duty cleaners attack grease, soap scum and ground-in soil. Aqua Mix Grout Deep Clean, made by Custom Building Products, is typical: its data sheet calls for a 5 to 10 minute dwell, agitation with a nylon brush, a thorough rinse, and about two hours of drying before any sealer goes on.
  • Acidic brighteners (Zep’s Grout Cleaner and Brightener is the best-known) dissolve mineral staining fast, with a label dwell of only about two to three minutes. That speed is why they are risky: the label excludes marble, terrazzo, travertine, natural stone and metal fittings, and repeated use eats into cement grout itself. Treat them as a one-off rescue on ceramic or porcelain, rinse very thoroughly, and never make them your weekly cleaner.

Follow the product’s own label over any article — including this one.

Level 5: Steam

A steam cleaner with a small nozzle and brush attachment loosens embedded dirt with heat and water alone. Work slowly along each line in short passes and wipe the loosened slurry away at once, otherwise it resettles in the pores as it cools. Two limits: steam will not fix cracked or crumbling grout, and MAPEI’s care FAQ warns that some pre-mixed grouts can be damaged by heat held on them too long. Keep the nozzle moving.

If it is mould, treat it differently

Mould on shower grout usually feeds on the soap and skin-oil film on the surface, which is why it scrubs off — and why it comes back if the film and the damp come back. The US Environmental Protection Agency’s mould cleanup guidance is deliberately unglamorous: scrub mould off hard surfaces with detergent and water, and dry completely. The agency does not recommend bleach as a routine part of household mould cleanup, and chlorine bleach has a real drawback on porous grout — it can fade the surface colour while growth inside the pores survives, so the line looks clean and reappears within weeks.

Work through it like this:

  1. Ventilate, glove up, and scrub with detergent and hot water, as in Level 1. For stubborn staining on white grout, the Level 2 peroxide paste is a reasonable next step.
  2. Rinse, then dry properly — towel it and leave the fan running. The EPA’s guide to mould and moisture in the home puts moisture control, not chemistry, at the centre: clean the mould and fix the water problem, or it returns.
  3. Never paint, caulk or seal over mouldy grout. That traps growth underneath a clean-looking skin.

Know the limits of a DIY job. The EPA suggests homeowners can usually handle a mouldy area of less than about 10 square feet (roughly 3 ft × 3 ft). A bigger area, a musty smell from behind the wall, mould returning within days, or growth on crumbling grout all point to water behind the tiles — a repair problem, worth a professional look.

Cleaners and tools that quietly do damage

  • Vinegar and other acids, used routinely. Acid dissolves the cement binder in grout. MAPEI states that even diluted vinegar can damage cement-based grout, and that regular use discolours and weakens it. One targeted use on mineral crust, on ceramic only, is a judgement call; a weekly vinegar spray is slow vandalism.
  • Chlorine bleach as a habit. MAPEI’s FAQ allows occasional diluted bleach (about one cup in a gallon of water, when disinfecting is genuinely needed), but warns that regular use can discolour and weaken grout. On coloured grout the fading can be permanent. Never on stone, and never mixed with anything.
  • Wire brushes and aggressive drill brushes. Bristles harder than the grout sand it away a little every time, widening the line and giving future dirt more room. A stiff nylon brush is as hard as you should go.
  • Oil-based soaps and wax-heavy cleaners. They leave a film in the pores that grabs new dirt, so grout looks worse sooner. MAPEI recommends pH-neutral cleaners for routine care.
  • Toilet-bowl cleaners and other strong acids. Far too aggressive for grout joints; they can etch tile glaze and burn skin. If it is sold for descaling sanitaryware, it does not belong on a grout line.

Dry it, then seal it: the step that makes the clean last

Unsealed cement grout starts re-absorbing dirt the first time you mop. A penetrating sealer soaks into the pores and slows that down. It does not waterproof grout, and sealing over grime locks the grime in — so the sequence matters:

  1. Clean first, then let the grout dry fully. After a deep clean, give it at least 24 hours, longer in a steamy bathroom; run a fan to help. Custom Building Products’ instructions for its TileLab Grout Sealer start from the same point: clean, dry and free of waxes or old finishes. (Brand-new grout is different — it must cure first, typically 48 to 72 hours.)
  2. Apply the sealer to the joints only, liberally, with the bottle’s applicator, a small brush or a sponge applicator. Let it penetrate for about five minutes, then wipe off all the excess from the tile face — sealer left to dry on glazed tile leaves a residue.
  3. If the first coat soaked straight in, apply a second the same way. Porous grout often drinks two coats.
  4. Test it. After about two hours, put a few drops of water on a joint. If the water darkens the grout as it soaks in, it needs another coat; if it sits on top, the joint is sealed.
  5. Keep the area dry while it cures — the same data sheet gives about two to three hours’ drying before normal use.

Expect to repeat this every year or two in a shower, less often on a dry floor; use the water-drop test rather than the calendar.

If the grout is clean but still stained: recolour it

Sometimes the scrubbing works and the colour does not come back. Staining can soak deeper than any cleaner reaches, and more scrubbing just wears the joint down. A grout colorant is the middle step between cleaning and regrouting. MAPEI’s UltraCare Grout Refresh is typical: a ready-to-use colourant and sealer in one that bonds to cement, epoxy, urethane and acrylic grouts and seals against common stains as it goes.

The rules are simple. Clean first and let the grout dry — colourant over dirt seals the dirt in. Apply a thin coat along the joint with a small brush, keep it off the tile face, and wipe away excess before it sets. Dark-to-light changes may take more than one coat, an hour or two apart, and the surface needs about 24 hours for its initial cure. Grout pens work the same way, in a smaller package.

Habits that keep grout clean longer

How often should you clean grout? Lightly, as part of the weekly bathroom or kitchen clean, with the deep ladder above kept for when the lines actually darken — that rhythm beats one brutal annual session. The appliances living in the same damp room follow the same clean-it-then-dry-it logic — see how to clean a washing machine.

  • Squeegee or towel shower walls after use. Grout that dries fast grows far less mould.
  • Run the extractor fan during a shower and for 20–30 minutes after, and keep indoor humidity below 60% where you can — the EPA’s moisture-control range.
  • Clean weekly with the pH-neutral cleaner, and wipe up coloured spills — curry, red wine, hair dye — promptly.
  • Fix dripping taps and failing silicone promptly — a leaky faucet left dripping keeps one patch of grout permanently wet, and constantly wet grout never gets the dry spell that keeps it clean.

When cleaning will not fix it

Sometimes the honest answer is that the grout itself has failed:

  • Lines that are cracked, crumbling, powdery or falling out in chunks
  • Grout that rocks or sounds hollow, or tiles that move — water is likely behind them
  • Black staining that returns within days of a proper clean
  • Joints worn well below the tile edge, leaving sharp tile corners exposed

That is regrouting territory: the old grout is raked or ground out, the joint repacked with fresh grout, cured and sealed. It is a dusty, slow job — on a small bathroom wall a realistic weekend project; floors with widespread failure are better handed to a tiler. Diagnose before you spend: if the grout is sound, the ladder above will clean it; if it is failing, cleaning is polishing a repair bill.