How to get mould out of shower grout (and keep it out)

By Adelaide Tile & Grout · Updated 2026-10-31 · Adelaide SA

Why shower grout goes mouldy

Mould needs three things: moisture, warmth and food. A shower supplies all three every day. Soap residue and skin oils settle into the grout lines, the room is warm, and if the window stays shut and the fan runs for a minute, the recess never dries out between showers. Adelaide bathrooms are worst in winter, when the house is closed up for months, but an internal ensuite with no window grows mould all year.

Cement grout makes it worse. It is porous, so it soaks up water and soap like a sponge, and mould roots into it rather than sitting on top. That is why a wipe-over lightens it for a week and then it comes back. Adelaide’s hard water adds a limescale film over the top that the mould grips even better.

How to clean mould off grout yourself

1. Ventilate and protect yourselfOpen the window, run the exhaust fan, wear gloves and keep kids and pets out. Never mix cleaning products: chlorine bleach plus vinegar or ammonia releases toxic gas.
2. Dry-brush the groutRun a stiff grout brush along the lines while they are dry to knock off loose growth and soap scum, then rinse.
3. Make a pasteMix oxygen bleach powder (sodium percarbonate, sold as laundry soaker) with a little warm water into a paste. 3% hydrogen peroxide from the chemist works too. Both are safe on cement grout and coloured grout.
4. Apply and waitWork the paste into the grout lines with an old toothbrush or grout brush. Leave it 10–15 minutes. Don’t let it dry out; mist it with water if it does.
5. ScrubScrub along the grout line, not across it, with a stiff nylon brush. Not a wire brush: it scratches tiles and tears grout.
6. Rinse and dryRinse with clean water, then dry the grout with a towel and leave the fan running. Mould regrows fastest in grout that stays wet.
7. Repeat if needed, then stopA second round shifts most surface mould. If the lines are still dark after two goes, the staining is in the grout, and more scrubbing won’t fix it. That is the point to book a professional clean.

Budget about 45 minutes for an average shower recess, longer if the grout hasn’t been done in years.

What not to do

• Chlorine bleach as your main cleaner. It bleaches the surface of the grout so it looks better for a while, but it doesn’t remove what has soaked in, it fades coloured grout, and the fumes are harsh in a small room. If you use it, use it last, diluted, and never with anything else.
• Mixing products. Bleach with vinegar or ammonia-based cleaners produces toxic gas.
• Wire brushes or abrasive pads. They scratch glazed tiles and tear soft grout out of the joints.
• Acids on natural stone or terrazzo. Vinegar, lemon and acidic tile cleaners etch marble, travertine, limestone and terrazzo permanently.
• Pressure washers indoors. They drive water behind the tiles.

Is it in the grout or in the silicone?

Look at where the black is. Grout lines run between tiles. Silicone is the flexible bead in the corners, along the base of the walls and around the screen. Mould in grout can be cleaned. Mould in silicone usually can’t: it grows inside the rubber, so cleaning only lightens it. Replacing the silicone is a tiler’s job, normally done as part of a shower regrout, which we quote after an inspection.

When DIY won’t fix it

• The grout stays grey or black after two proper rounds of paste and scrubbing
• The whole recess is affected, not just the corners and the bottom rows
• The tiles feel slippery or dull all over from soap scum and scale
• Someone in the house has asthma or allergies and the mould keeps returning

At that point the problem is staining inside the grout, and the fix is a proper clean: a treatment matched to the problem, every grout line scrubbed, and the dirty solution rinsed out and extracted rather than left to dry back in. Our shower and bathroom tile cleaning is $149 for a shower recess and $229 for a bathroom, with every price published.

Keeping it away afterwards

• Run the exhaust fan during the shower and for 20–30 minutes after. In winter, longer.
• Squeegee the walls and glass after each shower. Thirty seconds, and it removes most of the water mould needs, and most of the scale.
• Leave the door open so air moves through the room.
• Wipe the grout weekly with a mild bathroom cleaner. Little and often beats a big scrub twice a year.
• Seal the grout. Sealed grout absorbs less water and soap, so it dries faster and mould has less to hold onto. Clear sealing adds $69 to a shower clean.