Quick Answer

Mould in your Melbourne home is caused by excess moisture — most commonly from poor ventilation, condensation, rising damp, or roof/plumbing leaks. Black mould (Cladosporium or Stachybotrys) is the most common type found on walls, ceilings, and grout in Australian homes, and while surface mould can often be removed with vinegar or commercial cleaners, widespread or recurring mould indicates a moisture problem that must be fixed at the source. Health risks include respiratory irritation, allergic reactions, and worsened asthma — particularly serious for children, elderly, and immunocompromised residents.

What Causes Mould in Melbourne Homes?

Melbourne’s climate creates ideal conditions for mould growth. Cool, damp winters combined with older housing stock (many homes built before 1980 have no vapour barriers or ceiling insulation) mean moisture accumulates in wall cavities, under floors, and behind wall linings. Understanding the cause is the only way to solve the problem permanently — cleaning mould without fixing the source means it returns within weeks.

Poor Ventilation

The most common cause in Melbourne homes, especially in bathrooms, laundries, and kitchens. When warm, moist air from showers, cooking, and laundry can’t escape, it condenses on cool surfaces — walls, ceiling, window frames, and grout. Homes built with aluminium windows from the 1980s and 1990s are particularly susceptible because the frames conduct cold and attract condensation.

Condensation on Walls and Windows

In winter, indoor air is warmed by heating while exterior walls remain cold. Water vapour in the air hits the cold wall surface and condenses. Over time this saturates the wall lining and mould establishes behind paint or in the plaster. Thermal bridging through brick veneer or weatherboard with minimal insulation makes this worse in SE Melbourne suburbs like Berwick, Narre Warren, and Officer where overnight temperatures regularly fall to 5–8°C from June to August.

Rising Damp

Common in homes over 40 years old, particularly brick construction. Ground moisture wicks upward through masonry foundations when the damp-proof course (DPC) has failed or was never installed. Signs include a waterline stain 300–900mm above floor level, salt deposits (efflorescence) on brickwork, and persistent musty smell even after cleaning. Rising damp is a structural moisture problem requiring a licensed waterproofing specialist — it cannot be solved by painting over it.

Roof or Plumbing Leaks

A slow roof leak or a dripping pipe inside a wall cavity creates exactly the warm, dark, wet environment that mould needs. You may not see water — just a growing damp patch, stained paint bubbles, or mould appearing in a location that makes no sense for condensation (e.g., the middle of a wall, away from windows). If mould recurs after cleaning in the same spot, suspect a hidden leak.

How to Identify the Type of Mould

Not all mould in Australian homes requires professional remediation. Identifying the type and extent guides your response.

Mould Type Appearance Common Location Risk Level
Cladosporium Dark green or black spots, powdery texture Bathroom grout, window seals, tile surfaces Low–Medium (allergenic)
Aspergillus Green, yellow or brown patches, velvety Walls, ceiling, air conditioning vents Medium (respiratory irritant)
Penicillium Blue-green, fuzzy growth Wet walls, carpet, wallpaper Medium (allergenic)
Stachybotrys (Black Mould) Slimy black/dark green, wet appearance Persistently wet surfaces, flooded areas High — professional removal recommended
Pink/orange growth Pink or orange slimy patches Shower floor, grout, silicone Low (bacteria, not mould — different treatment)
Pro tip: You cannot reliably identify mould species by colour alone — only laboratory testing can confirm type. For practical purposes: if the mould is larger than an A4 sheet, appears slimy/wet rather than dry/powdery, or returns within a week of cleaning, treat it as high-risk and consider professional assessment.

Health Risks of Mould Exposure

The Victorian Government and Australian Department of Health recognise indoor mould as a significant health risk. Exposure via breathing airborne spores or skin contact can cause:

  • Nasal congestion, sneezing, and runny nose
  • Eye and throat irritation
  • Skin rashes and itching
  • Worsening of asthma and chronic respiratory conditions
  • Headaches and fatigue in sensitised individuals
  • In severe cases (Stachybotrys exposure): haemorrhagic lung disease, neurological symptoms
Safety warning: Children under 5, the elderly, pregnant women, and people with asthma, allergies, or compromised immune systems are at significantly higher risk. If any household member has respiratory symptoms that improve when away from home and worsen on return, mould exposure should be investigated immediately.

How to Remove Mould — Step by Step

Step 1: Prepare Safely

Before touching mould, put on an P2 respirator mask (not a dust mask), rubber gloves, safety glasses, and old clothes you can wash immediately. Open windows to ventilate the room. Turn off any recirculating air conditioning to avoid spreading spores through ductwork. Seal the doorway to the rest of the house with plastic sheeting for large remediation jobs.

Step 2: Choose the Right Cleaner

For surface mould on non-porous materials (tiles, glass, painted walls with intact paint):

  • White vinegar (undiluted): Most effective for bathroom mould — apply, leave 30 minutes, scrub with a stiff brush, rinse. Safe for most surfaces.
  • Clove oil solution: Quarter teaspoon clove oil per litre of water — a traditional Australian method that kills mould spores and reduces regrowth. Do not rinse after application.
  • Commercial mould cleaners (Selleys, White King Mould Killer): Effective but check surface compatibility. Follow label dwell times.
  • Bleach (sodium hypochlorite): Kills surface mould on non-porous surfaces but does NOT kill mould in porous materials (grout, plaster, timber). Also bleaches staining, giving a false impression the problem is solved.
Safety warning: Never mix bleach with vinegar, ammonia, or other cleaning products — toxic chlorine gas is produced. Use one product at a time and rinse thoroughly between products.

Step 3: Remove Surface Mould

Scrub the affected area with your chosen cleaner using a stiff brush. For tile grout, a grout cleaning brush or old toothbrush reaches into the joint profile. Work from the edges of the mould growth inward to avoid spreading spores. Place used cloths and brushes in a sealed bag immediately after use.

Step 4: Treat Porous Surfaces Differently

Plasterboard (gyprock), MDF, carpet, and soft furnishings absorb mould into the material — surface cleaning only removes what’s visible. If mould has penetrated more than 2mm into plasterboard or you can see discolouration through the other side of thin gyprock, the affected section should be cut out and replaced. This is a job for a licensed builder or plasterer if structural framing is involved.

Step 5: Address the Moisture Source

This is the step most homeowners skip, and why mould returns. After cleaning, fix the moisture problem:

  • Install or upgrade bathroom exhaust fans (minimum 25L/s airflow for a standard bathroom — check the capacity printed on your current fan)
  • Run exhaust fans during AND for 20 minutes after showers
  • Seal window frame gaps with silicone
  • Improve subfloor ventilation if rising damp is confirmed
  • Fix dripping taps, leaking shower bases, or roof leaks

When to Call a Professional

DIY mould removal is appropriate for contained surface mould on non-porous surfaces. Call a licensed mould remediation specialist when:

  • Mould covers more than 1 square metre in total
  • Mould is inside wall or ceiling cavities (you can smell it but not see it)
  • Mould returns within 2–3 weeks of cleaning, indicating a hidden moisture source
  • Any household member has unexplained respiratory symptoms or allergic reactions
  • Stachybotrys (slimy black mould) is present on porous surfaces
  • Rising damp has been confirmed (requires a licensed waterproofing contractor)

Mould remediation by a professional in Melbourne typically costs $300–$800 for a single room and $1,500–$4,000+ for whole-of-house remediation including structural drying. This does not include fixing the underlying moisture source, which is quoted separately by the relevant trades (plumber, roofer, waterproofer).

Troubleshooting: Why Does My Mould Keep Coming Back?

Symptom Most Likely Cause Fix Required
Returns within 2 weeks in bathroom Exhaust fan undersized or not used long enough Upgrade fan to 25L/s minimum; run 20 mins post-shower
Appears on external wall only, 600mm above floor Rising damp — failed DPC Licensed waterproofing contractor to inject silicone DPC
Spreading patch on ceiling, not near bathroom Roof leak or condensation in roof cavity Roofer to inspect for cracked tiles or failing flashing
On window frames and glass Condensation from cold surfaces — poor glazing Draught-proof window seals; consider secondary glazing
Behind furniture on external walls Cold bridging through wall; insufficient air circulation Move furniture 50mm from wall; improve room heating and ventilation
In wardrobe on external wall Cold, still air in wardrobe with no airflow Leave wardrobe door ajar; use desiccant sachets; improve insulation

Tips and Gotchas

  1. Never paint over mould. Paint is not a mould treatment — mould will grow through the new paint layer within weeks. Always remediate first, then repaint with anti-mould primer.
  2. Silicone sealant hides mould. Black silicone around baths and showers is usually mould that has colonised the sealant, not the silicone colour. You cannot clean mould from silicone — it must be cut out and replaced.
  3. Humidity above 70% triggers growth. A $25 indoor hygrometer lets you monitor moisture. Target below 55% relative humidity in living areas and bedrooms.
  4. Air conditioning can spread mould. Spores circulate through ducted systems. If you have mould and ducted AC, have the ductwork inspected before running the system.
  5. Thermal imaging finds hidden mould. Plumbers and building inspectors use thermal cameras to find cold, wet spots inside walls without opening them up. Costs around $200–$400 for an inspection.
  6. Renters have legal rights. Under the Victorian Residential Tenancies Act, landlords must maintain rental properties free of mould caused by structural defects. Report in writing and keep records.
  7. Insurance coverage is limited. Standard home insurance excludes gradual moisture damage and mould. Sudden and accidental water damage (burst pipe, storm leak) may be covered — check your policy’s water damage definitions.
  8. Clove oil prevents regrowth. After treating mould, spray diluted clove oil solution (1/4 teaspoon per litre) on cleaned surfaces and do not rinse. This significantly extends the period before regrowth.

Local Resources for Melbourne Homeowners

For mould removal products, testing, and professional remediation in Melbourne’s south-eastern suburbs:

Frequently Asked Questions

Is black mould in my bathroom dangerous?

Most black mould in Melbourne bathrooms is Cladosporium — a common allergenic mould that causes respiratory irritation but is rarely life-threatening for healthy adults. True Stachybotrys chartarum (toxic black mould) requires persistently wet conditions (not just humid) and is less common. However, any recurring black mould should be treated promptly — if household members experience respiratory symptoms, consult a GP and arrange professional testing.

Can I stay in my house while mould is being removed?

For small DIY jobs (bathroom tile grout, window seals), staying home with good ventilation is fine. For professional whole-room or whole-house remediation, contractors typically recommend vacating during the work and for several hours after — the containment, HEPA vacuuming, and air scrubbing process disturbs significant quantities of spores. Ask your contractor for specific advice based on the extent of the job.

How much does mould removal cost in Melbourne?

Professional mould remediation in Melbourne costs approximately $300–$800 for a single bathroom or room, and $1,500–$4,000+ for extensive whole-house treatment. These costs do not include fixing the moisture source (plumbing, roofing, waterproofing), which adds $200–$2,000+ depending on the cause. DIY products for a bathroom job cost $20–$60.

Will a dehumidifier stop mould?

A dehumidifier helps manage moisture in problem rooms but does not fix structural moisture sources. Running a dehumidifier in a room with rising damp or a roof leak is like bailing a boat with a hole — it reduces visible symptoms without solving the cause. Use dehumidifiers as a temporary measure while you identify and fix the moisture source, not as a permanent solution.

How do I know if I have rising damp or condensation?

Rising damp shows a waterline stain at a consistent height (typically 300–900mm above floor level), salt deposits on brickwork, and may appear on internal and external wall faces simultaneously. Condensation appears on cold surfaces — windows, window frames, upper walls near ceilings — and is worse in winter mornings. Rising damp is typically worse in winter as ground moisture levels increase, and appears on lower sections of walls regardless of ventilation.

Does vinegar really kill mould?

Yes — white vinegar (acetic acid at 5–8% concentration) kills approximately 82% of mould species on non-porous surfaces, according to research cited by the Environmental Protection Agency. It is effective, inexpensive, and safe for most surfaces. Apply undiluted, leave for 30–60 minutes before scrubbing, and do not dilute with water — this reduces effectiveness. Follow up with a clove oil solution spray (do not rinse) to inhibit regrowth.