Quick Answer

Mould in Australian homes is almost always caused by excess moisture — from condensation, leaks, or poor ventilation. Small patches under 1 m² can be safely removed DIY using a white vinegar or dilute bleach solution with proper PPE. Patches larger than 1 m², mould inside wall cavities, or mould recurring after cleaning indicate an unresolved moisture problem that needs professional assessment. The cause must be fixed — not just the mould surface-treated — or it will return within weeks.

Treating a surface mould patch in a bathroom corner — P2 mask, rubber gloves and eye protection are
Treating a surface mould patch in a bathroom corner — P2 mask, rubber gloves and eye protection are essential, and the exhaust fan should be running throughout to carry spores outside rather than through the rest of the house.

Why Mould Grows in Australian Homes

Mould is a fungus that grows wherever moisture, a food source (dust, timber, paint), and moderate temperatures combine. In SE Melbourne, mould problems peak in autumn and winter when:

  • Homes are heated, raising indoor humidity through cooking, showering, and breathing
  • Cold exterior walls create condensation surfaces when warm air contacts them
  • Windows stay closed for weeks, preventing moisture from escaping
  • Leaking roofs, gutters, or plumbing go unnoticed in enclosed spaces

The most common mould species found in Australian homes is Cladosporium (green-black surface mould) and Aspergillus/Penicillium species (grey or green patches). The less common but more serious Stachybotrys chartarum (true black mould) grows on wet cellulose surfaces like plasterboard and timber when sustained wetness is present for weeks or months.

Health Risks by Mould Type and Exposure Level

Mould Type Appearance Health Risk Common Location
Cladosporium Green-black spots Low–moderate; triggers allergies and asthma Bathroom tiles, window seals, walls
Aspergillus/Penicillium Grey, blue-green patches Moderate; respiratory irritant Behind furniture, ceiling corners
Stachybotrys (black mould) Slimy black patches High; mycotoxins can cause serious symptoms Wet plasterboard, timber framing
Alternaria Dark grey-brown velvety Moderate; asthma trigger Shower grout, bathroom corners
Trichoderma White, light green Low–moderate Damp timber, subfloor spaces
Safety warning: Do not attempt to identify mould type by appearance alone — professional air quality testing is required for a definitive identification. If anyone in your household has respiratory symptoms, asthma, or allergies that correlate with time spent at home, arrange professional mould testing before attempting any removal.

Where Mould Hides in Melbourne Homes

Visible surface mould on walls and tile grout is only part of the problem. Mould frequently grows in hidden locations:

  • Behind vinyl wallpaper and paint blistering on cold exterior walls
  • Inside wall cavities where condensation drains onto bottom plates
  • Under carpets and vinyl flooring on concrete slabs (condensation from below)
  • Inside ducted heating and cooling systems (spores circulate through the whole house)
  • In subfloor spaces with inadequate ventilation — common in older Frankston, Mordialloc and Dandenong homes
  • Around window reveals and behind curtains on cold single-glazed windows

Checking under vinyl flooring for hidden mould growth — condensation from cold concrete slabs freque
Checking under vinyl flooring for hidden mould growth — condensation from cold concrete slabs frequently causes mould to develop beneath floor coverings without any visible signs on the surface.

DIY Mould Removal: Step-by-Step

For surface mould patches under 1 m² on non-porous surfaces (tiles, painted walls, glass), DIY removal is appropriate provided you follow correct procedure.

What You’ll Need

  • P2/N95 respirator mask (not just a dust mask)
  • Safety goggles (non-vented)
  • Nitrile gloves (not latex)
  • Disposable cleaning cloths or old rags (bag and bin after use)
  • White vinegar (undiluted) OR dilute bleach solution (1 part bleach to 10 parts water)
  • Spray bottle
  • Plastic bags for waste disposal

Removal Method

  1. Ventilate the room — open windows and run the exhaust fan throughout. This carries spores out rather than through the house.
  2. Mist lightly before disturbing — spray the mould patch lightly with water or vinegar to prevent dry spores from becoming airborne.
  3. Apply vinegar or bleach solution — spray generously and leave for 10–15 minutes. White vinegar (undiluted) kills approximately 82% of mould species; bleach solution is more effective on non-porous surfaces.
  4. Wipe with disposable cloth — work from the outside edge of the patch inward to avoid spreading spores. Bag the cloth immediately after use.
  5. Dry the surface completely — mould regrows on damp surfaces within 24–48 hours. Run a dehumidifier or fan heater in the room for several hours after cleaning.
  6. Address the moisture cause — if you don’t fix the humidity, ventilation, or leak that caused the mould, it will regrow within 2–4 weeks.
Pro tip: White vinegar is safer than bleach for use in enclosed spaces and is equally effective on most common household mould species. Use undiluted white vinegar (not cleaning vinegar concentrate) from a spray bottle. Bleach works better on non-porous surfaces like tiles but is ineffective on porous surfaces like timber, where it bleaches but doesn’t kill mould roots.

When to Call a Professional

Situation Action
Mould patch larger than 1 m² Professional remediation — risk of spreading spores through HVAC
Mould inside wall cavity or behind plasterboard Professional assessment — plasterboard may need replacing
Mould returns within 2 weeks of cleaning Moisture source not resolved — investigate with professional
Musty smell with no visible mould Hidden mould — consider air quality test
Household members with respiratory symptoms Vacate affected room; get professional mould testing first
Mould in HVAC ducts or air handler Professional duct cleaning required — DIY risks spreading spores

Preventing Mould Regrowth

Mould prevention requires keeping indoor relative humidity below 60% and eliminating cold surfaces where condensation occurs. In SE Melbourne homes, the most effective prevention measures are:

  1. Run bathroom exhaust fans during and for 15 minutes after showering — many people turn them off too soon
  2. Vent the clothes dryer outdoors — indoor drying dramatically raises humidity in winter
  3. Open windows briefly each morning — even 10–15 minutes flushes overnight moisture from sleeping and breathing
  4. Keep furniture away from external walls — the gap allows air circulation and prevents moisture pockets
  5. Insulate cold external walls — the warmest intervention; prevents condensation surfaces forming
  6. Use a hygrometer to monitor humidity — available from hardware stores for $15–$30; aim for 40–55% RH indoors

Running a bathroom exhaust fan during and after showering is the single most effective mould prevent
Running a bathroom exhaust fan during and after showering is the single most effective mould prevention step — it removes moisture before it can condense on cold walls and tile grout.

Mould Cleaning Products: What Works and What Doesn’t

Product Effectiveness Best For Limitations
White vinegar (undiluted) Good — kills ~82% of species Painted walls, grout, glass Strong smell temporarily; not for bleachable surfaces
Dilute bleach (1:10) Excellent on non-porous Tiles, glass, chrome Ineffective on timber/plaster (bleaches only, doesn’t kill roots)
Clove oil solution (1/4 tsp per litre) Good — prevents regrowth Painted surfaces Strong smell; stains some surfaces
Hydrogen peroxide (3%) Good — antifungal Tiles, grout, bathroom surfaces Bleaches some coloured grout
Anti-mould paint (e.g. Zinsser) Moderate — suppresses not eliminates High-humidity rooms Treats symptom only if moisture cause not fixed
Tea tree oil spray Moderate Light surface mould Expensive; strong smell; not as effective as vinegar
Expert advice: For bathroom tile grout specifically, a paste of bicarb soda and white vinegar applied with an old toothbrush is highly effective for light mould. Leave for 10 minutes, scrub, and rinse. For persistent grout mould, re-grouting with anti-fungal grout (contains mould inhibitors) is a better long-term solution than repeated cleaning.

Local Melbourne Resources

Frequently Asked Questions

Is mould in my house dangerous?

Most common household mould causes respiratory irritation, allergy symptoms, and worsening asthma in sensitive individuals. Prolonged exposure to high mould spore counts — particularly in bedrooms — is associated with chronic respiratory problems in children. True black mould (Stachybotrys) is rare but produces mycotoxins that can cause serious symptoms. If household members are experiencing unexplained health symptoms, professional mould testing is advisable before attributing the cause to mould.

Does bleach kill mould on walls?

Bleach kills mould on non-porous surfaces (tiles, glass, sealed paint) but does not penetrate porous materials like timber, plasterboard, or unsealed grout. On porous surfaces, bleach removes the surface colour of mould but leaves the hyphae (roots) intact, meaning it grows back quickly. For porous surfaces, white vinegar or clove oil solution is more effective. The critical step regardless of product is fixing the moisture source — without that, mould regrows within 2–4 weeks on any surface.

How do I stop mould coming back after cleaning?

The only reliable way to stop mould returning is to fix the moisture source. For condensation mould (the most common type), this means improving ventilation (exhaust fans, morning window-opening), reducing indoor humidity (no indoor drying of clothes, fitting dryer vents to outside), and insulating cold exterior walls. Anti-mould paint applied after cleaning helps suppress surface regrowth but won’t prevent it if humidity remains above 60%.

Do I need to replace plasterboard with mould on it?

If mould has penetrated into the plasterboard (you can see it through the thickness, or the board is soft and crumbling), the plasterboard should be replaced — cleaning the surface doesn’t remove mould that has grown through the paper and gypsum. Surface mould on intact, firm plasterboard can often be treated without replacement using anti-mould primers and repaint. A licensed builder or mould assessor can assess whether remediation or replacement is required.

What is the best mould-resistant paint for bathrooms in Australia?

Zinsser Perma-White Mould & Mildew-Proof interior paint is widely regarded as the most effective mould-inhibiting paint available in Australia. Dulux Wash&Wear and Wattyl I.D. Interior also offer mould-inhibiting formulations suitable for bathrooms. All anti-mould paints work best on previously mould-free surfaces — they suppress regrowth on clean painted surfaces but will not kill established mould beneath paint layers.

Here’s the Bottom Line

Mould in a Melbourne home is almost always a symptom of excess moisture, not an independent problem. Clean the mould with white vinegar and proper PPE, but identify and fix the moisture source — whether that’s condensation from poor ventilation, a roof or plumbing leak, or damp entering from the ground.

For small patches, a weekend DIY job with white vinegar, an exhaust fan, and some improved ventilation habits will permanently resolve most cases. For anything larger than 1 m², recurring mould, or mould in a hidden location, invest in a professional assessment — the remediation cost is almost always lower than the long-term health and structural damage from untreated mould.