Top Signs of Mould Growth in Your Home and What to Do About It

At Water Damage Restoration Melbourne, we’ve been helping Melbourne homeowners and businesses for over 20 years, tackling mould safely and keeping homes healthy.

In this article, you’ll learn the top signs of mould, why they matter, what causes them, how to check safely, and when to call a professional. We’ll also share prevention tips straight from our technicians, so you know the advice comes from real, hands-on experience.

Why Identifying Mould Early Matters

Detecting mould (mold) early protects indoor air quality, building materials, and household health, it’s not just about appearance.

• Health risks: According to World Health Organization (WHO), exposure to mould spores can aggravate allergies, asthma, sinus infections, eczema, and even cause respiratory infections, especially in children, elderly people, and individuals with compromised immune systems.
• Property risks: Mould can degrade plaster walls, timber frames, gypsum board, insulation, floor coverings, and HVAC systems. Over time, unchecked moisture and biological growth can threaten the structural integrity of your home.
• Financial risks: Prompt remediation is far less costly than major water damage repairs, structural repairs, or insurance claims. Addressing mould promptly reduces mould removal costs, lowers property devaluation, and prevents escalating maintenance expenses.

Visible Signs of Mould Growth

Look carefully in your home, apartment, or commercial building for these signs:

1. Discolouration and stains

Yellow, brown, green, or black marks on plaster walls, ceilings, wallpapers, cornices, floor tiles, or skirting boards may signal mould or water intrusion.

2. Peeling or bubbling paint

Paint lifting, cracking, or blistering can indicate moisture retention behind gypsum boards, plaster, or wood panels.

3. Fuzzy or slimy growth on surfaces

Spotted or patchy growth on bathroom tiles, window sills, timber, fabric upholstery, or silicone seals often points to active mould colonies.

Invisible Signs You Shouldn’t Ignore

Not all mould is visible but some signs show up as air quality issues or health symptoms:

4. Musty, damp, or earthy odours

A persistent smell resembling wet socks, damp earth, or old books, especially in basements, bathrooms, or closed-off rooms can signal hidden mould.

5. Unexplained allergies or asthma

Frequent sneezing, coughing, runny nose, itchy eyes, or worsened asthma attacks indoors can result from inhaling mould spores or mycotoxins.

6. Ongoing headaches or fatigue

Feeling tired, mentally foggy, or experiencing recurrent headaches at home without clear cause may be linked to mould-induced indoor air pollution.

Common Hidden Spots Where Mould Thrives

Even in a clean-looking home, mould can hide in these high-risk areas:

• Behind kitchen cabinets and under sinks. Areas near leaky pipes, dishwashers, or sink plumbing are prone to moisture buildup.
• Under carpets and in subfloor spaces. Carpet underlays, timber subfloors, and concrete slabs can trap dampness, especially after spills or floods.
• Inside roof cavities, attics, and behind insulation. Poor ventilation, roof leaks, and condensation behind fibreglass or foam insulation create perfect mould conditions.
• Inside HVAC systems, air ducts, and air conditioning units. Air handlers, ductwork, and split systems can harbour mould, spreading spores throughout your home.

What Causes These Signs? (Environmental Triggers)

These environmental conditions often set the stage for mould growth:

• Leaking pipes or taps – Dripping from plumbing joints, water supply lines, or under sinks creates persistent moisture.
• Roof leaks or blocked gutters – Water intrusion from damaged roofing, flashing failures, or clogged gutter systems can seep into ceilings and walls.
• Condensation on windows or walls – Moisture build-up on single-pane windows, aluminium frames, or cold wall surfaces signals humidity problems. According to CSIRO, condensation is a major contributor to hidden dampness in Australian buildings and requires proper management to prevent long-term damage
• Poor ventilation in bathrooms, kitchens, or basements – Inadequate exhaust fans, rangehoods, or subfloor ventilation traps humid air indoors.
• Previous flooding or storm damage – Past flood events, stormwater ingress, or seepage through foundations can leave behind hidden damp zones.

Legal Steps for Tenants and Landlords Dealing with Mould in Melbourne

Mould isn’t just a nuisance, it’s a legal responsibility under Victorian tenancy law, especially in rental properties. Both tenants and landlords have rights and obligations under the Residential Tenancies Act 1997 (Vic).

For Tenants

• Report mould issues promptly: Notify your landlord or property manager in writing as soon as you notice mould, damp patches, or water leaks. Early reporting strengthens your legal position.
• Document evidence: Take photos, videos, and keep copies of emails, letters, or SMS. This provides proof if the landlord fails to act.
• Know your rights: Under the Residential Tenancies Act (Vic), landlords must provide and maintain a habitable property. Unresolved mould caused by structural or moisture issues may breach this duty. According to Consumer Affairs Victoria, tenants have the right to request urgent repairs, and landlords are legally required to act promptly to maintain a safe, habitable property.
• Seek help if needed: If the landlord doesn’t respond, tenants can contact Consumer Affairs Victoria or apply to VCAT (Victorian Civil and Administrative Tribunal) for a repairs order or rent reduction.

For Landlords

• Act quickly on reports: Landlords are responsible for repairing leaks, improving ventilation, addressing rising damp, and remediating structural defects that cause mould.
• Organise professional assessment: For serious or recurring mould, hire licensed mould remediation specialists to assess, treat, and issue a mould clearance certificate.
• Communicate transparently: Provide tenants with a clear action plan, including repair timelines, access arrangements, and updates.
• Understand legal obligations: Failure to address mould can lead to compensation claims, VCAT orders, fines, and even landlord insurance disputes.

Expert Tip: Mould disputes often escalate due to poor communication. Landlords and tenants should cooperate to fix both the visible mould and the underlying moisture source (e.g., leaking pipes, roof damage, poor ventilation) to prevent future problems.

How to Check for Mould Safely at Home

Follow these safe mould inspection steps before deciding on DIY or professional help:

1. Look
   Inspect walls, ceilings, floors, skirting boards, and hidden areas like under sinks or behind appliances for stains or discolouration.
2. Touch
   Check for damp spots, soft plaster, warped timber, or loose tiles that may signal hidden moisture.
3. Smell
   Trace any musty odours, similar to wet socks or damp earth, especially near basements, laundries, or bathrooms.
4. Tools (if available)
   Use moisture meters, thermal imaging cameras, or hygrometers to detect hidden damp areas behind surfaces.
5. Know when to stop
   If the mould patch is larger than 1 square metre, or you experience dizziness, allergic reactions, or breathing difficulties, call a professional mould removal service, DIY can be hazardous.

What to Do If You Spot the Signs

1.  Small patch (about the size of a dinner plate)
   For minor mould spots, you can tackle them yourself using white vinegar or a mild detergent mix but don’t skip safety gear! Always wear protective gloves and an N95 mask to avoid breathing in harmful mould spores.
2. Bigger area (over 1 square metre or spreading)
   When mould covers a larger area or keeps coming back, it’s time to call in the pros. At Water Damage Restoration Melbourne, we bring in specialised mould remediation tools, antifungal treatments, and containment systems to remove mould safely and stop it from spreading through your home.
3. Fix the cause, not just the surface
   Cleaning mould is only half the battle. To keep it from returning, fix what’s causing it: repair leaking pipes, boost ventilation with exhaust fans or dehumidifiers, and manage indoor humidity levels to create a dry, mould-resistant environment.

Natural Remedies vs. Chemical Treatments: What Works Best for Mould Removal?

When tackling mould (mold) at home, choosing the right method depends on the surface type, mould extent, and environmental safety needs. Here’s how natural treatments and chemical treatments compare and when each works best.

Natural Remedies

1. White vinegar – Effective against 80% of mould species. Apply undiluted to non-porous surfaces (tiles, glass, stainless steel), leave for 1 hour, scrub with a stiff brush.
2. Baking soda (sodium bicarbonate) – Mild antifungal and odour neutraliser. Mix with water, spray on affected areas, scrub, and rinse.
3. Tea tree oil (Melaleuca alternifolia oil) – Natural antifungal and antibacterial; mix 1 teaspoon per cup of water, spray on surfaces, leave without rinsing for continued protection.

When it works best:

• Small patches under 1m².
• Hard, sealed surfaces (e.g., bathroom tiles, kitchen splashbacks, sealed countertops).
• Households with children, pets, or people sensitive to chemical fumes.

Limitations:

• Ineffective on porous materials like plasterboard, timber frames, or carpet underlays.
• Doesn’t stop recurrence if underlying moisture (leaks, humidity) isn’t fixed.

Chemical Treatments

1. Commercial mould removers (sodium hypochlorite/bleach-based) – Kills surface mould and whitens stains; works best on non-porous materials.
2. Hydrogen peroxide (3%) – Antifungal and antiviral; penetrates slightly into porous surfaces like timber and fabric.
3. Professional fungicides / antimicrobials – Specialist treatments used by mould remediation experts; designed for deep mould removal in wood structures, gypsum boards, HVAC systems, and air ducts.

When it’s necessary:

• Large or recurring mould infestations.
• Mould on porous or semi-porous materials (e.g., plaster walls, timber skirting boards, HVAC ductwork).
• Post-flooding or after major water damage events.

Caution:

• Bleach is not recommended on porous surfaces; it may worsen mould spread. The US Environmental Protection Agency (EPA) notes that while bleach may kill surface mould on non-porous materials, it is ineffective on porous materials like drywall, wood, or carpets, where mould can quickly regrow.
• Always wear personal protective equipment (PPE); gloves, N95 mask, goggles and ensure good ventilation.

Expert Tip: Regardless of the product, fixing the moisture source (e.g., plumbing leaks, roof damage, high humidity, poor ventilation) is essential. Cleaning without addressing the cause means mould will keep returning.

How to Prevent Mould After Finding It

• Improve ventilation – Open windows regularly and use exhaust fans in kitchens, bathrooms, and laundries to reduce indoor humidity.
• Control moisture levels – Run dehumidifiers in damp-prone areas like basements, subfloors, or bathrooms to keep relative humidity below 60%.
• Fix leaks promptly – Repair plumbing leaks, roof leaks, or gutter blockages as soon as they’re detected to prevent hidden dampness.
• Schedule professional inspections – After any flooding, storm damage, or major water intrusion, book a professional check to ensure no hidden mould remains behind walls or under floors.

When Should You Call a Mould Expert?

Knowing when to stop DIY and bring in a professional can save your health, home, and wallet. Here’s when it’s time to call for expert help:

1. The mould patch is larger than 1 square metre
   Big or fast-spreading mould problems need professional remediation to ensure safe removal and prevent spores from contaminating other areas.
2. Health symptoms are getting worse indoors
   If you or your family are dealing with worsening allergies, asthma flare-ups, skin rashes, or difficulty breathing at home, hidden mould may be affecting your indoor air quality.
3. You suspect hidden mould behind walls or floors
   Mould loves dark, damp places and it can hide under floorboards, inside insulation, or in roof cavities, where only professional tools like moisture meters and thermal cameras can detect it.
4. There’s mould inside HVAC or air conditioning systems
   Once mould spreads into HVAC ducts, split systems, or air handlers, it can circulate spores throughout your home, making professional cleaning essential.

Worried about mould in your home or business? Water Damage Restoration Melbourne offers thorough mould inspections, honest advice, and expert solutions to keep your home or workplace safe, healthy, and mould-free.

Conclusion

Mould might be small, but it’s no small matter. Early action protects your health, your home, and your wallet.

If you’re seeing signs or just want peace of mind, Water Damage Restoration Melbourne is here to help. Reach out today for expert mould removal and prevention services across Melbourne.

Frequently Asked Questions

Will bleach kill mould permanently?

No, bleach will not kill mould permanently, especially on porous materials. Bleach can remove surface mould on non-porous materials like tiles, glass, or stainless steel, but it doesn’t penetrate porous materials such as plasterboard, timber, or carpets.

Most importantly, using bleach doesn’t fix the underlying moisture problem. Without addressing leaks, condensation, or high humidity, mould is likely to return, no matter how thoroughly you clean the surface.

Can I just dry out mould with a fan or heater?

No, drying out mould with a fan or heater will not kill mould spores or remove contamination. While fans and heaters can help reduce moisture, they do not eliminate mould. In fact, blowing air on a mouldy surface can aerosolize mould spores, spreading them through the indoor air and increasing risks of asthma attacks and breathing difficulties, respiratory exposure, allergic reactions (sneezing, itchy eyes).

How do I know if the mould is completely gone?

You’ll know mould is completely gone when professional remediators confirm it using clearance checks and air quality testing.

Experts use:

• Moisture meters to check for hidden dampness in walls, ceilings, and floors
• Thermal imaging cameras to detect moisture behind surfaces
• Air sampling tests to measure indoor mould spore levels

Simply wiping away visible mould stains is not enough, complete mould removal means:

• Eliminating hidden contamination in porous materials (like drywall, insulation, timber)
• Fixing water leaks and condensation issues
• Improving ventilation systems to control humidity
• Ensuring all affected areas are dry, stable, and safe