Mould in grout comes off with the right method: a bicarb paste or a diluted bleach solution for surface stains, plenty of ventilation, and a stiff brush. The harder truth is that if it keeps returning, cleaning is not the answer. The grout has usually lost its seal, and the real fix is better airflow and, in many cases, a regrout.
This guide covers how to remove mould from grout safely, why it keeps coming back in Adelaide bathrooms, and how to tell when scrubbing is a waste of time and regrouting is the fix. It sits within our Tile Repairs, Regrouting and Restoration in Adelaide guide.
How to remove mould from grout safely
Most bathroom mould is surface mould sitting on top of the grout, and it responds to a gentle approach before you reach for anything harsh.
Start with the gentle method
Mix bicarb soda with a little water into a thick paste. Spread it along the mouldy grout lines, leave it for 10 minutes, then scrub with a stiff nylon brush (an old toothbrush works for corners). Rinse with warm water and dry the surface with a cloth. This lifts most light mould without fumes and is safe around children and pets.
For a bit more punch, white vinegar in a spray bottle left for 30 minutes before scrubbing kills many mould types. Do not mix vinegar and bleach, and do not mix bleach with any other cleaner. The combination releases toxic fumes.
Step up to bleach only when needed
For stubborn black staining, use a diluted bleach solution (roughly 1 part bleach to 4 parts water) or a dedicated bathroom mould spray. A few safety rules that matter in a small Adelaide bathroom:
- Open the window and run the exhaust fan the whole time.
- Wear gloves and old clothes, and keep the door open for airflow.
- Apply, wait a few minutes, scrub, then rinse thoroughly.
- Never mix cleaning products.
If the grout looks clean while wet but the black returns the moment it dries, the mould is inside the grout, not on it. No amount of scrubbing will fix that, and you are into repair territory rather than cleaning.
Why mould keeps coming back
Scrubbing the same grout lines every few weeks is the most common complaint we hear, and it is almost never a cleaning-product problem. It is an environment problem. Mould needs moisture, warmth and something porous to grow into, and a typical bathroom hands it all three.
Poor ventilation is the number one cause
Adelaide gets cold, damp winters and humid summer stretches, and a lot of older homes in areas like the inner west and the Hills have bathrooms with a tiny window and no working exhaust fan. Steam has nowhere to go, so it settles on the coldest surfaces (the grout and silicone) and stays wet for hours. That is a perfect mould nursery.
Practical fixes that make the biggest difference:
- Run the exhaust fan during the shower and for 20 to 30 minutes after.
- Leave the door open after showering so the room dries out.
- Squeegee or wipe the walls and screen after a shower.
- If there is no fan, an extractor fan is one of the highest-value bathroom upgrades you can make.
Unsealed or failing grout lets moisture in
Grout is porous. When the sealer wears off (or was never applied), water soaks into the grout, sits there, and mould grows from the inside out. This is why sealing matters. Keeping grout sealed is far cheaper than repairing water damage later, and you can see typical figures in our guide to grout sealing cost in Adelaide.
If the grout is also cracked or crumbling, sealing will not save it. Cracks let water straight through to the substrate, and our guide on whether to repair or replace cracked grout walks through how to judge which situation you are in.
When cleaning stops working and regrouting is the fix
There is a clear line where cleaning becomes a waste of effort. Use this quick comparison to work out which side you are on.
| Situation | What it means | The right fix | | --- | --- | --- | | Surface mould, grout intact | Cosmetic, sealer is holding | Clean and reseal | | Mould returns within days | Poor ventilation or worn sealer | Fix airflow, then reseal | | Black staining right through the grout | Mould is embedded in porous grout | Regrout the affected area | | Cracked, crumbling or missing grout | Seal has failed, water getting behind | Regrout | | Mould across a whole wall or floor | Possible moisture problem behind tiles | Inspection, then regrout or repair |
Regrouting means raking out the old grout, cleaning the joints, and laying fresh grout that can be sealed properly. It is the point where the problem actually stops, because you are removing the mould-infested material rather than bleaching over it. Grout pens and paint only coat the surface and peel in a wet area, so they are a false economy in a bathroom.
The cost depends on the size of the area and how much old grout has to come out. Our regrouting cost in Adelaide guide has current price bands, and as a rough guide a standard bathroom regrout typically lands in the $400 to $900 range depending on size and condition, less than the cost of repairing water damage that embedded mould can hide.
If the mould keeps returning across a large area, or you can smell damp behind the tiles, that can point to a waterproofing failure rather than a grout problem. That is worth having a licensed tiler inspect before you spend money on cosmetic fixes, and it is exactly the kind of job our tile and grout regrouting service is built to sort out.
Keep mould from coming back
Once the grout is clean or freshly laid, a simple routine keeps it that way:
- Ventilate every shower and dry the surfaces.
- Reseal grout on the recommended schedule for your sealer.
- Deal with cracks and gaps early, before water gets in.
- Wipe silicone corners weekly, since they hold moisture longest.
Get the mould sorted properly
If you have scrubbed the same grout lines more than a couple of times, the grout is telling you something. Tell us about your bathroom and we will connect you with vetted, licensed Adelaide tilers who can inspect the grout, tell you honestly whether it needs cleaning, sealing or a full regrout, and quote it properly. Get free quotes with no obligation.