How to clean grout: what works, what doesn’t, and when to stop

By Adelaide Tile & Grout · Updated 2026-11-01 · Adelaide SA

First, work out what you’re cleaning

Grout is a cement sponge. What darkens it is one of four things, and each wants a different cleaner: grease and dirt (kitchen and living-room floors; wants an alkaline degreaser), mould (showers; wants oxygen bleach or peroxide), hard-water scale (Adelaide showers; wants a scale remover, never on stone), or staining that has gone right through (old grout; no cleaner fixes it, colour sealing does). A dab of 3% peroxide that fizzes means mould; no fizz means dirt. Our guide to why grout goes black has the one-minute test. And check the surface: terrazzo, slate, marble and travertine are damaged by anything acidic, so only neutral or alkaline products near them.

Method 1: baking soda and hydrogen peroxide paste

The best all-round home method for cement grout, floors or showers. Cheap, safe on coloured grout, and the peroxide deals with mould while the baking soda gives you a mild abrasive.

1. Vacuum, then dry-brushGet grit and loose dirt out first so you are not grinding it into the lines. Run a stiff nylon grout brush along the dry lines.
2. Mix the pasteThree parts baking soda to one part 3% hydrogen peroxide, into a thick paste. For greasy kitchen grout add a squeeze of dishwashing liquid. Nothing acidic on terrazzo, slate or natural stone.
3. Apply and wait 10 to 15 minutesWork it into the lines with an old toothbrush or grout brush. Keep it damp; mist it with water if it dries.
4. Scrub along the lineStiff nylon brush, along the grout line rather than across it. Not a wire brush and not an abrasive pad: both scratch tiles and tear soft grout.
5. Rinse, then remove the waterRinse with clean water and towel or wet-vac the floor dry. Leaving dirty rinse water to dry on the floor puts some of the dirt straight back.
6. Judge it dry, then decideWait until the grout is fully dry before deciding. If it is still patchy after two rounds, the staining is inside the grout and more scrubbing will not fix it.

Budget about an hour for a shower recess or a small kitchen floor. It is hard on the knees; a long-handled grout brush helps on floors.

Method 2: oxygen bleach soak (floors)

Sodium percarbonate, sold as laundry soaker or “oxygen bleach”, is the strongest home option for greasy, grey floor grout and it is safe on coloured grout. Dissolve it in hot water per the packet, mop it on generously so the grout lines are flooded, leave it 15 to 30 minutes without letting it dry, scrub along the lines with a deck brush, then rinse with clean water and wet-vac or towel the floor dry. Two rounds on a neglected floor. Not for natural stone (it is alkaline, which is fine, but the soaking can mark some stone), and keep it off timber skirtings.

Method 3: steam cleaners

Handheld and upright steam cleaners are popular and the national search numbers show it. Here is the honest picture. Steam loosens surface grime and kills mould on contact, so on grout that is already fairly clean and sealed, a steam mop is a decent way to maintain it. On neglected grout it has two problems: it makes dirty water and has no way to remove it, so the grime tends to go deeper; and the heat and wetness shorten the life of any sealer that is there. If you own one, use it after a chemical clean to rinse, and wet-vac or towel behind it. Don’t buy one to fix black grout.

Method 4: hire a grout cleaning machine

Hire rotary scrubbers do the agitation well and save your knees. What most hire units lack is extraction: they scrub the loosened dirt into a slurry that you then have to mop up, and mopping puts some of it back into the lines. Hire for a day plus chemicals usually lands close to the cost of a professional clean of one room, and the result depends on the pre-treatment you use, not the machine. If you hire, pre-treat with an alkaline cleaner, let it dwell, scrub, then rinse with clean water and remove it with a wet-vac rather than a mop.

Bottled grout cleaners: what matters on the label

• Alkaline (degreaser-type) cleaners suit floors, kitchens and general grime. This is what professionals use on floors.
• Oxygen-based (percarbonate, peroxide) suit mould and organic staining, and are safe on coloured grout.
• Acidic cleaners and “grout haze” or scale removers dissolve hard-water film and cement haze. Never on terrazzo, slate, marble, travertine or limestone, and not repeatedly on cement grout, which they slowly erode.
• Chlorine bleach products whiten the surface and kill mould but don’t remove soaked-in dirt and fade coloured grout.
• “Shine” or polish products leave a film that holds dirt. Skip them.

Price and brand tell you little; the chemistry on the back tells you everything. Test any product in a hidden spot first.

What wrecks grout

• Wire brushes and abrasive pads: they scratch glazed tiles and tear grout out of the joint
• Vinegar, lemon and acidic sprays on terrazzo, slate or natural stone: permanent etching
• Mixing bleach with vinegar or ammonia cleaners: toxic gas
• Pressure washers indoors or on grout outdoors: water driven behind the tiles, grout blown out
• Leaving dirty rinse water to dry on the floor: it goes straight back into the lines
• Sealing grout before it is clean and fully dry: the dirt is locked in

When to stop and call someone

If the grout is still grey or patchy once fully dry after two proper rounds, the staining is inside the cement and more scrubbing only wears the grout. At that point a professional clean does three things you can’t at home: a stronger pre-treatment matched to the soiling, machine agitation of every line, and extraction of the dirty solution so nothing dries back in. In Adelaide our grout cleaning is $149 for a shower recess, $229 for a bathroom and $8 per square metre for floors, with every price published. Where a shadow remains, colour sealing gives one even colour; where grout is cracked or crumbling, it is a regrout, not a clean.

Once it is clean, seal it. Sealed grout is the difference between mopping and scrubbing next year.