Quick Answer
Black mould on bathroom grout responds to a baking soda paste or diluted bleach spray left for 30–60 minutes — most stains lift with a stiff brush and no professional help. Pink mould (Serratia bacteria) needs the same treatment. Mouldy silicone that has turned black all the way through must be cut out and replaced — no cleaner removes deep silicone mould permanently. Budget $20–$80 for DIY cleaning and $80–$250 to have silicone professionally re-done.
Melbourne’s humid winters and poor bathroom ventilation in older homes make mould on grout and silicone one of the most common maintenance problems homeowners face. Whether it’s the grout lines in your shower or the silicone bead along the shower screen, here’s how to treat it and prevent it from coming back.
Mould on Grout vs Mould on Silicone: Key Difference
The most important thing to know before you start cleaning is whether you’re dealing with surface mould on grout (cleanable) or deep mould inside silicone (not cleanable — replace it).
| Type | What It Looks Like | Fix |
|---|---|---|
| Surface mould on grout | Black/grey staining on grout surface; grout still firm | Clean with bleach or mould remover |
| Deep mould in grout | Black staining that doesn’t shift after cleaning; grout crumbly | Re-grout affected sections |
| Surface mould on silicone | Pink or grey film on silicone surface | Clean with bleach-soaked cotton wool; dry well |
| Deep mould inside silicone | Black specks visible through silicone; doesn’t lift with cleaning | Remove silicone entirely and replace |
| Pink slime (not mould) | Pink/orange film on silicone or tray | Bleach spray; improve ventilation |
How to Remove Mould from Grout
Method 1: Bleach Spray (Most Effective for Dark Mould)
Mix 1 part household bleach with 3 parts water in a spray bottle. Spray generously onto the mouldy grout and leave for 30–60 minutes — don’t rinse immediately. The longer the dwell time, the more mould spores the bleach kills. Scrub with a stiff grout brush (or old toothbrush for detail work), then rinse thoroughly with water.
Method 2: Baking Soda Paste (Gentler, Good for Light Mould)
Mix baking soda with a small amount of water to make a thick paste. Apply it to the grout lines and scrub immediately with a stiff brush. Add a few drops of white vinegar to the paste to boost the reaction (add the vinegar after the paste is in place — not before, or it neutralises). Rinse with water. This method is safer for coloured grout and won’t bleach surrounding surfaces.
Method 3: Commercial Mould Remover (Ready-to-Use)
Products like HG Mould Remover Foam, White King Bathroom Mould Remover, and Selleys No More Mould are available at Bunnings and most supermarkets. These contain bleach-based active ingredients in a gel or foam formula that clings to grout without running. Apply, leave 20–30 minutes, scrub, and rinse. They’re more expensive than DIY bleach solution but easier to apply in vertical grout lines.
How to Remove Mould from Silicone
If the Mould is Surface-Level
Soak cotton wool pads or cotton coils in neat household bleach (don’t dilute for this application). Press them tightly against the mouldy silicone bead and leave for 2–4 hours, or overnight for persistent staining. Remove the cotton, spray with bleach solution, scrub with a toothbrush, and rinse. Dry the silicone completely after cleaning — moisture is what feeds mould regrowth.
If the Mould is Deep Inside the Silicone — Replace It
No cleaner removes mould that has colonised the interior of a silicone bead. The silicone appears black through the surface and the discolouration doesn’t shift with any product. The only fix is to cut it out and replace it completely.
DIY silicone replacement steps:
- Score both edges of the old silicone bead with a sharp knife or silicone removal tool ($8–$15 at Bunnings)
- Pull or cut out the old bead — it should come away cleanly once both edges are cut
- Remove all residue with a silicone remover spray (Selleys, $12–$18) or methylated spirits on a cloth
- Dry the joint completely — wait 24–48 hours if possible
- Apply low-mould bathroom silicone (Selleys Wet Area or Parfix Bathroom Silicone) in a smooth bead
- Smooth with a wet finger or silicone tool; remove excess immediately before it skins
- Leave 24 hours before getting wet
Why Mould Keeps Coming Back in Melbourne Bathrooms
Melbourne’s cool, damp winters create near-perfect mould conditions in bathrooms that don’t have adequate ventilation. The most common reasons mould returns after cleaning:
- No exhaust fan, or a fan that doesn’t duct outside. Many older Melbourne homes have exhaust fans that recirculate into the ceiling cavity rather than ducting to the eaves — they move air but don’t remove moisture.
- Door closed during and after showering. Keeping the door closed during a shower traps humidity in the room for hours after.
- Ungrouted or cracked grout. Water wicking into the substrate behind tiles feeds mould at the root level — surface cleaning doesn’t reach it.
- Silicone older than 7–10 years. Old silicone loses its anti-mould additives and becomes porous, making deep colonisation inevitable.
Prevention: How to Stop Mould Coming Back
- Run the exhaust fan during every shower and for 20 minutes after. Check that your fan actually ducts outside — hold a tissue to the grille while it runs; it should pull toward the grille firmly.
- Leave the bathroom door ajar after showering. Air circulation dries the bathroom faster than any exhaust fan alone.
- Squeegee the shower walls after every use. Removing standing water from tiles and screens is the single most effective mould prevention habit.
- Re-seal grout annually. Grout sealer (penetrating or topical) dramatically reduces moisture absorption. Apply after cleaning and wait for the grout to be fully dry.
- Replace old silicone every 7–10 years. Modern mould-resistant bathroom silicone contains biocides that prevent mould colonisation — old silicone loses these additives over time.
- Use mould-resistant paint in the bathroom. If you’re repainting, specify bathroom/kitchen formulation paint with mould inhibitors.
Cost Summary
| Task | DIY Cost | Professional Cost |
|---|---|---|
| Clean grout mould | $5–$25 (bleach/products) | $80–$200 (cleaning service) |
| Re-grout shower (per m²) | $30–$80 materials | $150–$350/m² labour + materials |
| Remove and replace silicone (shower) | $20–$50 materials | $80–$250 per bead |
| Bathroom exhaust fan upgrade | Not DIY (electrical) | $150–$400 including fan |
Local Melbourne Resources
- Bunnings — Mould Remover & Bathroom Cleaning Products
- Selleys — Bathroom Silicone and Mould Remover Range
- Better Health Victoria — Mould Health Information
- hipages — Find a Tiler or Bathroom Specialist in Melbourne
FAQ
Does vinegar kill bathroom mould?
White vinegar is mildly antifungal and works on surface mould — spray undiluted, leave 30–60 minutes, scrub and rinse. It’s safer than bleach on coloured grout but less effective on heavy black mould staining. Never mix vinegar with bleach — the combination creates toxic chlorine gas.
Can I paint over mouldy grout?
Painting over mould does not kill it — the mould continues growing underneath the paint and eventually pushes through. You must remove the mould first, allow the surface to fully dry, then seal with a mould-resistant primer before painting.
When should I call a professional instead of DIY?
Call a professional if: the mould covers more than 1m² of grout (suggests systemic moisture ingress); the grout is crumbling and needs full re-grouting; the mould returns within a few weeks of cleaning (indicates a deeper moisture source); or you suspect mould is growing inside the wall cavity.
How long does new silicone last in a Melbourne bathroom?
Quality bathroom silicone (Selleys, Parfix, or similar brands) lasts 7–10 years in normal use before anti-mould additives deplete and the silicone begins to crack or discolour. Replace it proactively rather than waiting for it to fail completely.
Is the pink slime in my shower the same as black mould?
No — pink slime is usually Serratia marcescens bacteria, not mould. It responds to the same bleach cleaning approach. The real fix is reducing moisture: squeegee the shower after use, run the exhaust fan longer, and leave the door ajar. Unlike black mould, pink bacteria don’t indicate a structural moisture problem.
Final Thoughts
Surface mould on bathroom grout is a cleaning problem. Mould inside silicone is a replacement problem. Get that distinction right before you spend money on products that won’t fix the actual issue. For most Melbourne bathrooms, a $10 bottle of bleach, a stiff brush, and better ventilation habits will resolve most mould problems — and re-doing the silicone every 7–10 years prevents the deep colonisation that makes cleaning pointless.