Quick Answer
Bathroom mould on tiles, grout, and silicone is a common Melbourne winter problem — cold tiles plus condensation create ideal growing conditions. For patches under 1 m², white vinegar or a commercial mould killer like Exit Mould will clear it in under an hour. Always wear a P2 respirator and rubber gloves, treat the moisture source, and replace any mouldy silicone rather than scrubbing it — silicone is porous and scrubbing only removes the surface.
Melbourne winters bring exactly the conditions mould loves: cold tile surfaces, warm showers creating steam, and bathrooms that don’t dry out between uses. Homes in south-eastern suburbs like Berwick, Cranbourne, and Frankston — many built in the 1980s and 1990s with small, poorly ventilated bathrooms — are particularly prone to black grout lines and stained silicone beads by mid-June.
The good news: surface bathroom mould is one of the most straightforward DIY jobs in the house. This guide walks you through the process properly — including the step most people skip, which is why mould keeps coming back.
What You’ll Need
Safety gear (non-negotiable)
| Item | Cost | Where to get it |
|---|---|---|
| P2 respirator mask | $8–15 each | Bunnings, hardware stores, chemists |
| Safety goggles | $5–12 | Hardware stores |
| Heavy-duty rubber gloves | $8–12 | Supermarkets, hardware stores |
Tools and materials
| Item | Cost | Notes |
|---|---|---|
| Stiff-bristled grout brush | $5–10 | Mitre 10, Total Tools, hardware stores |
| Old toothbrush | $0 (reuse) | For tight corners and around tapware |
| Spray bottle | $3–5 | For vinegar solution |
| Microfibre cloths (4–6) | $8–15 per pack | Supermarkets, hardware stores |
| White distilled vinegar (2L) | $4–6 | Any supermarket — use undiluted |
| Commercial mould killer | $8–14 | Exit Mould, White King, Selleys Rapid Mould Remover |
| Bicarb soda | $2–4 | For stubborn grout staining — supermarket |
| Mould-resistant silicone sealant | $12–20 | For replacing mouldy silicone beads — Reece Plumbing, hardware stores |
| Grout sealer | $15–25 | Aqua Mix, Selleys — tile shops, Bunnings |
Step-by-Step: Removing Bathroom Mould
Step 1: Ventilate and Gear Up
Before you open any mould killer, ventilate the bathroom: open the window, turn on the exhaust fan, and prop the door open. If there’s no window, position a pedestal fan in the doorway blowing fresh air in. Then put on your P2 respirator, safety goggles, and rubber gloves — mould spores become airborne during scrubbing, and the chemicals in commercial mould killers are harsh on airways and eyes.
Step 2: Assess the Extent of Mould
Work around the room checking tiles, grout lines, silicone beads, the ceiling above the shower, and any painted walls near the shower rose. If the mould area totals more than 1 square metre, or if tiles sound hollow when tapped (suggesting water behind them), or if plasterboard walls feel soft or discoloured, stop — this is beyond surface DIY. See “When to Call a Professional” below.
For typical bathroom mould — black grout lines, stained silicone, and tile discolouration — proceed with the steps below.
Step 3: Apply Your Mould Treatment
White vinegar method (preferred for regular maintenance): Fill a spray bottle with undiluted white distilled vinegar and spray generously over all affected areas. Leave for 30–60 minutes — the acetic acid disrupts the mould’s cell structure. Don’t rinse before scrubbing.
Commercial mould killer (for heavier infestations): Products like Exit Mould Trigger Spray or White King Mould Killer typically require a 5–10 minute dwell time. Apply in a well-ventilated space. Note: these products contain bleach — they’ll discolour coloured grout.
Step 4: Scrub and Remove the Mould
Using your stiff grout brush, scrub in short circular motions along grout lines, tile faces, and around fittings. Use the old toothbrush for tight corners, tap bases, and the overflow drain area. For stubborn black grout staining that won’t shift, make a thick paste of bicarb soda and water, press it into the grout line, leave for 10 minutes, then scrub again. Rinse the area thoroughly with warm water and wipe dry with a microfibre cloth.
Step 5: Replace Mouldy Silicone — Don’t Just Scrub It
Silicone is porous. Once mould has penetrated the silicone bead (those rubbery strips at the base of the shower screen, around the bath, and at wall junctions), scrubbing only removes the surface layer — the mould inside the bead regrows within weeks. The only lasting fix is to cut out the old silicone and regrout with a fresh mould-resistant bead.
Use a grout saw or Stanley knife to cut along both edges of the silicone bead. Peel it out, clean the surface with sugar soap, and apply a new bead of mould-resistant bathroom silicone (Selleys 900 Mould Resistant, Bostik Waterproof Sealant, or similar). Smooth the bead with a wet finger or a caulk finishing tool. Leave to cure for at least 24 hours before exposing to water.
Step 6: Seal and Prevent Recurrence
Once the surfaces are dry, apply a mould-resistant grout sealer to all grout lines. This waterproofs the grout, dramatically reducing future mould penetration. Apply to clean, dry grout — sealing over dirty or mould-stained grout locks the problem in.
For ongoing prevention in Melbourne winters:
- Run your exhaust fan for at least 15–20 minutes after every shower
- Squeegee tile walls after each use
- Check your exhaust fan is actually venting outside — some older Melbourne homes have bathroom fans ducted into the ceiling cavity, which just redistributes spores
- Consider a mould-resistant paint on any painted bathroom walls (Dulux Wash & Wear + Bathroom/Kitchen)
Troubleshooting
| Problem | Cause | Fix |
|---|---|---|
| Mould returns within 2–4 weeks | Mould has penetrated silicone bead; surface scrubbing doesn’t reach it | Cut out and replace silicone with mould-resistant sealant |
| Black staining stays after scrubbing | Mould has penetrated porous grout | Re-grout affected sections with mould-resistant grout; seal after curing |
| Mould on bathroom ceiling | Exhaust fan insufficient — need ≥25 L/s output per AS 1668.2 | Upgrade exhaust fan or fit a timer switch; check duct is clear |
| Mould on large wall area (1 m²+) | Waterproofing failure behind tiles or within wall cavity | Call a licensed waterproofing contractor — not a DIY fix |
| Mould smell but no visible mould | Mould growing in wall cavity or behind plasterboard | Professional assessment required — probe tiles for hollow spots |
When to Call a Professional
DIY mould removal is appropriate for small surface patches on tiles, grout, and silicone. Call in a professional when:
- Mould covers more than 1 m²
- Mould is on or behind plasterboard/gyprock
- Mould returns repeatedly despite thorough treatment and ventilation fixes
- Tiles sound hollow when tapped (water behind them)
- Plasterboard feels soft, is discoloured, or is bubbling at the base of walls
- You suspect significant mould on porous substrates — this may require specialist remediation
In Victoria, large-scale mould remediation should follow Australian Mould Guideline (AMG) standards. For underlying waterproofing failures — failed membrane, cracked tiles over wet areas — you need a licensed waterproofing contractor. Verify registration at vba.vic.gov.au. For rental properties, tenants have rights to a mould-free home under the Residential Tenancies Act 2018 — notify your landlord in writing.
Top 10 Tips and Gotchas
- Never mix bleach and vinegar. Even residual vinegar on a surface can react with a subsequent bleach application — rinse thoroughly between treatments.
- Paper masks don’t protect against mould spores. Only P2 or N95 rated respirators provide adequate filtration.
- Vinegar damages natural stone. Don’t use vinegar on marble, travertine, or limestone tiles — it etches the surface. Use a stone-safe mould cleaner instead.
- Grout sealer must go on clean, dry grout. Sealing over even faint mould staining locks the problem in and accelerates regrowth.
- Check your exhaust fan is ducted outside. Fans ducted into ceiling cavities redistribute spores and moisture — a very common problem in pre-2000 Melbourne homes. The duct should vent through the roof or an external wall.
- Commercial mould killers bleach coloured grout. Test on an inconspicuous area first if your grout isn’t white.
- Cold walls in older Melbourne homes cause heavy condensation. If your bathroom is on an external wall with no insulation, adding wall insulation makes a bigger difference than any cleaning product.
- Don’t expose fresh silicone to water for 24 hours. Solvent-based silicones release strong fumes during curing — keep the bathroom ventilated.
- Mould killers don’t fix moisture problems. They bleach the staining, but if the exhaust fan is inadequate, mould regrows in weeks.
- A squeegee is the highest-ROI bathroom upgrade. A $15 window squeegee used after every shower removes 75–80% of the moisture mould needs — more effective than any spray treatment.
Local Melbourne Resources
- Reece Plumbing — mould-resistant silicone sealants, grout, bathroom products across Melbourne
- Bunnings — Exit Mould, White King, grout brushes, P2 respirators, and exhaust fans
- Mitre 10 — grout sealers, Selleys silicone range, cleaning tools
- Victorian Building Authority (VBA) — verify licensed waterproofing contractors and tradespeople
- Consumer Affairs Victoria — Renting: Repairs and Maintenance — tenants’ rights around mould and damp
Frequently Asked Questions
Does white vinegar actually kill bathroom mould?
Yes — undiluted white distilled vinegar (5% acetic acid) kills most common bathroom mould species on contact. The key is leaving it on for at least 30–60 minutes before scrubbing — a quick spray-and-wipe doesn’t give the acid enough dwell time to penetrate.
Can I use bleach on bathroom tiles?
Yes, diluted bleach (1 part bleach to 10 parts water) is safe on ceramic and porcelain tiles. However, undiluted bleach can damage chrome fittings, weaken silicone, and discolour coloured grout. Commercial mould killers like Exit Mould are formulated at the right concentration. Never use bleach on natural stone tiles (marble, travertine, limestone).
Why does mould keep coming back in my shower?
The three most common causes: (1) mouldy silicone that needs replacing rather than scrubbing — once mould is inside the bead it regrows no matter how thoroughly you clean the surface; (2) an exhaust fan that’s undersized or ducted into the ceiling cavity rather than outside; (3) cold external walls in older homes causing persistent condensation. Fix the silicone first, then address the ventilation.
How do I remove black mould from bathroom silicone?
Surface scrubbing only removes visible staining — mould regrows within weeks because the spores are embedded in the porous silicone. The correct fix is to cut out the old silicone bead entirely with a grout saw or Stanley knife, clean the area, and apply fresh mould-resistant silicone sealant. It takes about 30–45 minutes and a $15–20 tube of silicone.
Is bathroom mould dangerous to health?
Most common bathroom mould causes respiratory irritation, coughing, and allergy symptoms — particularly in people with asthma or immune conditions. Small surface patches on tiles are a manageable DIY job with proper PPE. Large infestations (over 1 m²) should be professionally assessed, especially if mould appears on porous materials like plasterboard.
What’s the best mould killer for Australian bathrooms?
Exit Mould Trigger Spray is widely recommended on forums like Whirlpool and r/AusRenovation — it’s effective on tiles and painted surfaces and the trigger-pack format makes application easy. For grout specifically, a bicarb paste followed by vinegar scrubbing penetrates more deeply than bleach-based products, which mainly bleach the staining without fully penetrating the surface.
Can I paint over bathroom mould?
No. Painting over mould traps it, but it grows through the paint within weeks — often causing visible bubbling and flaking. The surface must be fully cleaned, treated, and completely dry before painting. Use a mould-resistant paint product (Dulux Wash & Wear + Bathroom/Kitchen, or Taubmans Moisture Shield) for any repainted bathroom surfaces.
