Mould is one of the most common indoor environmental hazards in Australian homes. Estimates suggest between 10% and 50% of Australian dwellings have some degree of mould contamination — a range that reflects the country’s varied climate zones, from tropical Queensland to temperate Victoria. Yet many homeowners either ignore mould because they assume it is harmless, or panic because they assume all mould is toxic. The truth lies in the science: species identification through laboratory analysis is the only way to determine what you are dealing with and what it means for your health.

Why Mould Testing Matters

Mould is not merely a cosmetic issue. While the black spots on bathroom grout may seem like a minor nuisance, indoor mould growth is associated with a well-documented range of health effects. The World Health Organization’s guidelines on indoor air quality state that dampness and mould are consistently associated with respiratory symptoms, asthma exacerbation, and allergic rhinitis. In Australia, the CSIRO estimates that poor indoor air quality — of which mould is a major contributor — costs the economy billions annually in healthcare and lost productivity.

The health impact depends on two critical factors: the species present and the concentration of exposure. Some species, such as Cladosporium cladosporioides, are ubiquitous and generally cause mild allergic responses in sensitised individuals. Others, such as Aspergillus fumigatus, can cause life-threatening invasive infections in immunocompromised people. Stachybotrys chartarum produces trichothecene mycotoxins that are cytotoxic and immunosuppressive. You cannot determine species by looking at mould — laboratory analysis is required.

Beyond health, mould causes progressive structural damage. Fungal hyphae penetrate porous building materials — plasterboard, timber framing, carpet backing, wallpaper — breaking down cellulose and compromising structural integrity over time. Early detection and species identification through testing allows targeted, cost-effective remediation before damage becomes extensive.

Visible vs Hidden Mould: Why Testing Matters Even When You Can See It

A common misconception is that mould testing is only necessary when mould is not visible. In fact, testing visible mould serves a critical purpose: species identification determines health risk.

A patch of dark mould on a bedroom wall could be Cladosporium (common, allergenic but not toxigenic), Aspergillus niger (opportunistic pathogen, particularly concerning for those with respiratory conditions), Stachybotrys chartarum (toxigenic, requires specific remediation protocols), or any of dozens of other genera. Each has different health implications and may require different remediation approaches. Visual inspection cannot distinguish between them — even experienced assessors cannot reliably identify mould species by appearance alone.

Testing also provides actionable data. Settle plates analysed by an independent NATA-accredited laboratory will report the species identified and colony counts per plate. This information guides remediation decisions: low colony counts of Cladosporium suggest normal background levels, while colonies of Stachybotrys or Aspergillus on a settle plate indicate airborne spores from an active moisture source requiring investigation and remediation.

What a Proper Mould Air Test Kit Includes

A quality home mould air test kit, such as the Test Australia Mould Air Settle Plate Kit, should include the following components:

• 3× pre-poured agar settle plates — Laboratory-grade agar plates designed for passive air sampling. You place each plate open in a room for one hour, during which airborne mould spores settle onto the agar surface by gravity. After exposure, you seal the plate and return it for laboratory incubation and analysis.
• Sealable return bags — Pre-labelled, sealable bags for secure transport of exposed plates to the laboratory. Each bag corresponds to one plate and one sampling location.
• Instruction card — Clear, step-by-step guidance on where to place plates, how long to expose them, and how to seal and return them for analysis.
• Pre-paid return satchel — Postage-paid satchel for sending your sealed plates to our NATA-accredited partner laboratory (BMS Adelaide) for incubation and species identification.

How the Kit Works

The process is straightforward: open the plate lid, place the plate on a stable surface at approximately breathing height (~1 metre) in the room you want to test, and leave it undisturbed for one hour. Airborne mould spores settle onto the agar by gravity. After one hour, replace the lid, seal the plate in its return bag, and post all plates back to the laboratory using the pre-paid satchel. The laboratory incubates the plates for 3–5 days, then reports the species identified and colony count for each plate.

Where to Place Your Plates

For the three plates included in the kit, prioritise the rooms where you spend the most time or suspect the highest mould activity:

• Bedroom — Where you sleep for 6–8 hours per night, making prolonged inhalation exposure most significant.
• Living area — The room where you spend the most waking hours.
• Bathroom or kitchen — High-humidity areas where mould growth is most common.

Place each plate on a stable, flat surface at approximately breathing height (~1 metre from the floor) — a bedside table, shelf, or benchtop is ideal. Avoid placing plates directly on the floor, in direct airflow from fans or air conditioning vents, or in direct sunlight.

Limitations

Settle plate sampling is a useful screening tool for identifying what mould species are present in your indoor air. However, it is important to understand its limitations: settle plates provide qualitative species identification and indicative colony counts, but are not equivalent to professional calibrated impaction air sampling (such as Andersen or Zefon Air-O-Cell cassettes). Results from settle plates are influenced by air movement, particle size, and exposure conditions. Settle plate results are not suitable for insurance claims, legal proceedings, or tenancy disputes — these require quantitative air sampling conducted by a qualified assessor using calibrated equipment. For comprehensive, forensically defensible assessment, professional mould inspection is recommended.

Where to Test in Your Home

Strategic plate placement maximises the diagnostic value of your kit. Because settle plates capture airborne spores, focus on the rooms where you spend the most time and where moisture sources are present:

• Bedroom — You spend 6–8 hours per night breathing the air in this room. Place the plate on a bedside table or shelf at approximately breathing height (~1 metre). This is your highest-priority sampling location.
• Living area — The room where you spend the most waking hours. Place the plate on a shelf, side table, or benchtop away from direct airflow.
• Bathroom or kitchen — High-humidity areas where mould growth is most common. Place on a stable surface away from direct water splash. If you suspect a particular room, prioritise it here.

For each plate, choose a stable, flat surface at approximately breathing height (~1 metre from the floor). Avoid placing plates on the floor, in direct airflow from fans or air conditioning, near open windows, or in direct sunlight — these factors can affect which spores settle on the plate.

With 3 plates in the kit, the recommended approach is: one in the bedroom, one in the main living area, and one in the room you suspect has the worst mould or humidity issue (bathroom, kitchen, or laundry). This gives you comparative data across the spaces where you spend the most time.

Understanding Species Identification Results

Your laboratory report will identify the mould species present in each sample. Here is what the most commonly identified species mean for your property:

Cladosporium

The most common airborne mould genus in Australia and worldwide. Typically olive-green to dark brown or black. Found on almost every surface where moisture persists. Allergenic — can trigger hay fever, asthma, and sinusitis in sensitised individuals — but not classified as a primary toxigenic species. Its presence at low to moderate levels is expected; elevated indoor concentrations indicate excessive moisture.

Aspergillus and Penicillium

Often reported together as “Asp/Pen” because their spores are morphologically similar under standard microscopy. Both are extremely common indoors. Most species are allergenic. Aspergillus fumigatus is an opportunistic pathogen of significant concern for immunocompromised individuals. Aspergillus flavus produces aflatoxins (classified as Group 1 carcinogens by IARC in the context of ingested contaminated food). Elevated indoor Aspergillus/Penicillium levels almost always indicate a moisture source requiring attention.

Stachybotrys

Stachybotrys chartarum is the species commonly referred to as “toxic black mould.” It produces trichothecene mycotoxins and requires sustained water saturation of cellulose-based materials (plasterboard, ceiling tiles) for growth. Its presence is always significant and typically indicates serious water damage. Professional mould assessment and remediation by qualified specialists is recommended whenever Stachybotrys is identified.

Chaetomium

An indicator of severe, prolonged water damage. Like Stachybotrys, it colonises cellulose-based building materials under sustained wet conditions. Produces chaetoglobosins (cytotoxic metabolites). Its presence in a building should be taken seriously and investigated professionally.

DIY Remediation Limits vs Professional Intervention

Not all mould problems require professional intervention, but knowing the threshold is important.

When DIY Is Appropriate

You can safely manage mould yourself when the affected area is less than approximately 1 square metre, the mould is on non-porous surfaces (tiles, glass, metal, sealed benchtops), there is no suspected hidden mould behind walls or in cavities, and occupants are not immunocompromised or experiencing health symptoms. Use a microfibre cloth with household detergent — not bleach, which kills surface mould on non-porous materials but does not penetrate porous substrates and adds moisture that promotes regrowth.

When Professional Assessment Is Essential

Engage a qualified professional when mould covers more than 1 square metre, is growing on porous materials (plasterboard, timber, carpet), is present in HVAC systems (ductwork, air handling units), is suspected behind walls or in ceiling cavities (musty odour without visible growth), laboratory results identify toxigenic species (Stachybotrys, Chaetomium), occupants report health symptoms, or the results are needed for insurance claims, legal proceedings, or tenancy disputes.

Test Australia provides independent professional mould assessment including moisture mapping, air sampling, surface sampling, thermal imaging, and detailed reporting. We do not own, operate, or receive referral fees from any remediation company — ensuring our assessment findings are entirely impartial. For a professional assessment, contact us to discuss your situation.