Mould Testing and Air Quality Assessment — What IICRC Certified Contractors Do

Professional mould assessment uses multiple testing methods, selected based on the purpose of the assessment — initial scoping, species identification, or post-remediation clearance. Each method provides different information:

• Visual inspection — The foundation of any mould assessment. A trained inspector examines the property for visible mould growth, water staining, moisture intrusion points, condensation, and building conditions that support mould (high humidity, poor ventilation, leaks). Visual inspection guides where sampling is most useful.
• Tape lift and surface swab sampling — Tape lifts collect a sample of surface growth for microscopic analysis. Swabs collect material from within mould colonies for culture and species identification. These methods identify what species are growing on a particular surface and confirm whether a stain is mould or another substance.
• Bulk sampling — A small section of affected material (plasterboard, timber, carpet) is removed and sent to the lab for analysis. Used when surface sampling is insufficient to characterise the growth, or when material condition needs to be assessed for disposal versus retention decisions.
• Air cassette sampling (spore trap) — A calibrated pump draws a known volume of air through a cassette containing a sticky surface that captures airborne spores. The cassette is analysed by a mycology laboratory to identify and count spore types per cubic metre of air. This method measures the airborne spore load — the primary exposure risk — and is the standard method for clearance testing.
• ERMI (Environmental Relative Mouldiness Index) — A DNA-based dust sampling method that sequences mould species from settled dust. ERMI is used in some research and high-sensitivity assessments but is not standard in Australian remediation practice and is not required by IICRC S520.

Laboratory analysis of mould samples provides two key pieces of information: species identification and concentration. Both matter for assessing health risk and remediation scope.

• Species identification — Not all mould species carry the same health risk or indicate the same cause. Water-damage indicator species — Stachybotrys chartarum (“black mould”), Chaetomium, and Ulocladium — require prolonged wet conditions to establish and are rarely present in outdoor air. Their presence indoors strongly indicates a water damage event. Common environmental species — Cladosporium, Penicillium, Aspergillus — are ubiquitous and their presence must be interpreted in context of their concentration relative to outdoor levels.
• Spore concentration per m³ — Air sample results are expressed as spores per cubic metre (spores/m³). Concentration alone is not sufficient for interpretation — the species composition and the outdoor control sample are essential context. Indoor Stachybotrys at 50 spores/m³ is more significant than indoor Cladosporium at 5,000 spores/m³ if outdoor Cladosporium is 4,500 spores/m³.
• Comparison to outdoor control sample — Every professional air assessment should include an outdoor control sample taken at the same time as indoor samples. This establishes the baseline for the specific location and day, accounting for seasonal variation, regional climate, and proximity to vegetation. Indoor results are interpreted relative to this baseline.

Post-remediation clearance testing is the confirmation step that proves remediation was effective. It is not optional for any significant remediation project.

• Independent third-party requirement — Clearance testing should be performed by an assessor who was not involved in the remediation work. This independence prevents conflicts of interest — a contractor cannot reliably certify the quality of their own work. Insurers increasingly require third-party clearance certification.
• Outdoor control comparison — Clearance testing uses the same air cassette method as initial assessment, always including an outdoor control sample taken on the same day. Indoor spore concentrations are assessed relative to that day’s outdoor baseline.
• IICRC S520 clearance criteria — The IICRC S520 standard requires that after remediation, the property shows no visible mould, no mould odour, and indoor spore concentrations that do not significantly exceed outdoor baseline. Water-damage indicator species should be absent or at trace levels. The assessor issues a written clearance certificate confirming these criteria are met.
• Failed clearance — If clearance testing reveals elevated spore concentrations or visible growth, the remediation scope must be reviewed and additional work undertaken before re-testing. A failed clearance is not unusual — it simply means the initial scope did not capture all affected materials, and further investigation is required.

A common question is whether testing is necessary before remediation, or whether visible mould is sufficient to proceed directly to removal. The answer depends on the purpose of the assessment.

• Obvious visible mould over 0.1m² — The IICRC S520 standard considers any mould growth exceeding 0.1m² as requiring professional remediation regardless of species. If visible growth of this scale is present, remediation should begin without waiting for testing results. Testing before remediation helps scope the work but does not change the outcome — remediation is required.
• Testing before remediation to scope the work — Pre-remediation testing is useful when the extent of contamination is unclear, when hidden mould is suspected behind walls or under floors, or when the client or insurer requires documented pre-remediation conditions. Air sampling can detect elevated spore concentrations even when visible growth has not yet appeared.
• Testing after remediation is required — Post-remediation clearance testing is not optional for any professionally conducted remediation. It provides the documented evidence that work was completed to the IICRC S520 standard — required by insurers, landlords, and property purchasers. Skipping clearance testing leaves the property owner without proof that the remediation was effective.
• Testing for health concerns without visible mould — When occupants report health symptoms consistent with mould exposure but no visible growth is present, air sampling can confirm or rule out elevated spore concentrations. This scenario often reveals hidden mould within wall cavities, under flooring, or in HVAC systems.