Indoor Air Quality Testing and Mould: Air Sampling, Surface Sampling, and What Each Tells You

What “Mould Testing” Actually Means

“I need my house tested for mould” is something we hear regularly — but what people mean by “tested” varies considerably. There are several distinct methods for assessing mould in a building, and they provide different information. The right test depends on what question you’re trying to answer.

This guide covers the four main methods: visual inspection, moisture mapping, air sampling, and surface sampling — what each involves, what it tells you, what it doesn’t tell you, and when to use each.

Method 1: Visual Inspection

What it involves: A trained technician systematically inspects all accessible areas of the property — bathrooms, kitchens, laundries, all rooms, subfloor, roof void, and any areas with reported concerns — for visible mould, mould-related staining, and conditions that indicate elevated mould risk (water staining, efflorescence, deteriorating sealants, plasterboard deformation).

What it tells you:

• The location and approximate extent of visible mould
• Conditions that indicate mould risk even where mould isn’t yet visible
• The building’s general moisture vulnerability

What it doesn’t tell you:

• Whether mould is present in concealed spaces (wall cavities, subfloor, roof void) where it isn’t visible
• The concentration of mould spores in the air
• The specific mould species present

When to use it: Always — visual inspection is the foundation of every professional mould assessment. It should always be the starting point.

Can you DIY visual inspection? You can look for visible mould yourself, but a professional inspection adds moisture meter assessment, knowledge of subtle indicators of concealed mould, and the experience to interpret what you find. For most significant mould situations, a professional visual inspection is worth doing even if you’ve already identified visible mould.

Method 2: Moisture Mapping

What it involves: A calibrated moisture meter is used to take readings at consistent locations across all wall, ceiling, and floor surfaces throughout the property. Readings are recorded and mapped to identify areas of elevated moisture — including areas where moisture is elevated in the building material even where the surface appears dry.

What it tells you:

• Where moisture is elevated in building materials — indicating current or past water damage and potential for existing or developing mould
• Moisture pathways — which direction moisture is moving through the building fabric
• The likely source of moisture where there is elevated reading clustering

What it doesn’t tell you:

• Whether mould is actually present in elevated-moisture areas (moisture creates the conditions for mould; it doesn’t confirm mould is there)
• The species of mould present

When to use it: As a component of every professional mould inspection, and particularly for:

• Post-flood properties (Lismore, Casino, Murwillumbah)
• Properties with musty smell and no visible mould
• Pre-purchase inspections
• Properties with known water damage history

Can you DIY? Moisture meters are available retail ($30–$150), but interpretation requires experience. The pattern of readings across a property is more diagnostic than any single reading, and knowing what “elevated” means in the context of different building materials requires training.

Method 3: Air Sampling (Air Quality Testing)

What it involves: A sampling pump pulls a measured volume of air through a collection medium (either a cassette with a sticky surface or an impinger liquid) over a set period (typically five to ten minutes). The sample is sent to an accredited laboratory for analysis. Results identify the genera of mould spores captured and their concentration (spores per cubic metre of air). An outdoor sample is always taken simultaneously for comparison.

What it tells you:

• The concentration of mould spores in the indoor air at the time of sampling
• The genera (types) of mould present
• How indoor concentrations compare to the outdoor baseline — elevated indoor levels indicate active indoor mould growth
• Whether specific mould types of concern (e.g., Stachybotrys, Chaetomium) are present

What it doesn’t tell you:

• The exact location of the mould source (air sampling detects spores in the air; it doesn’t show where they’re coming from — this requires visual inspection and moisture mapping)
• The absolute amount of mould in the building (only spore concentrations in air at the time and location of sampling)
• If mould is dormant (not actively sporulating, dormant mould may not contribute elevated spore counts to room air)

When to use it:

• When concealed mould is suspected and visual inspection doesn’t confirm it (a musty smell with no visible mould)
• Post-remediation clearance testing — confirming that spore levels have returned to background after remediation
• Pre-purchase inspections for flood-affected properties or those with musty smell
• Insurance claims requiring objective mould quantification
• Landlord-tenant disputes requiring objective third-party evidence
• Where household members have health symptoms and mould is suspected

Can you DIY? See our DIY test kit vs professional testing guide for a detailed comparison. In short: DIY air sampling kits have significant limitations that make them inappropriate for insurance, legal, or medical purposes.

Method 4: Surface Sampling (Swab and Tape Lift Samples)

What it involves:

• Swab samples: A sterile swab is rubbed across a suspected mould surface and sent to the laboratory for culture and identification
• Tape lift samples: A piece of transparent tape is applied to the surface and lifted — collecting mould cells directly — then applied to a glass slide for microscopic analysis

What it tells you:

• Whether mould is present on the sampled surface
• The specific genera (and sometimes species) of mould present on that surface
• The relative density of mould on the surface

What it doesn’t tell you:

• Whether mould is present elsewhere in the building
• The airborne spore concentration
• Whether mould that appears to be surface-level has penetrated the substrate

When to use it:

• When a specific surface is suspected and you need confirmation or species identification
• When visual inspection has identified a suspicious discolouration but mould can’t be confirmed visually
• When species identification is important — e.g., to confirm or rule out Stachybotrys chartarum
• Post-remediation verification on a specific surface

Putting It Together: Which Tests Do You Need?

What Results Mean

Interpreting Air Sample Results

Air sample results are typically reported as spores per cubic metre (spores/m³). Key points for interpretation:

Outdoor baseline is essential. All indoor results must be compared to the outdoor baseline taken at the same time. Outdoor mould spore counts vary hugely by season, weather, and environment. In the Northern Rivers wet season, outdoor counts are naturally higher than in drier months. An indoor result of 500 spores/m³ means something different if the outdoor baseline is 200 (elevated indoors, indicating a source) vs 800 (likely reflecting outdoor air).

Species matter as much as counts. Some mould species are very common outdoors and their indoor presence may not indicate an indoor source. Others — particularly Stachybotrys chartarum and Chaetomium globosum — are rare outdoors and their indoor presence almost always indicates indoor moisture damage.

No single number is “safe” or “dangerous.” The IICRC and other bodies provide guidance, but there are no legally established “safe” thresholds for all mould genera in all situations. A professional will interpret results in the context of species, comparison to outdoors, and the clinical situation.

Frequently Asked Questions

How long does it take to get mould air sample results? Laboratory turnaround for standard mould air sampling is typically three to five business days. Expedited processing (one to two business days) is available at higher cost. We’ll discuss turnaround options when scheduling your inspection.

Do I need air sampling as well as visual inspection? For significant residential investigations — particularly flood-affected properties, musty smell with no visible mould, and health-related situations — air sampling adds meaningful objective information that visual inspection cannot provide. For small, clearly visible surface mould situations, visual inspection and moisture mapping are usually sufficient. We’ll recommend what’s appropriate for your specific situation.

Can air sampling tell me exactly where the mould is in my house? No. Air sampling tells you how many spores of which types are in the air in the sampled room. It doesn’t locate the source. Visual inspection, moisture mapping, and thermal imaging are the tools for locating the source. Air sampling confirms whether active sporulation is occurring in the sampled space.

Are there any health risks from having air sampling done? The sampling process itself poses no health risk — it’s a pump drawing air through a cassette. In fact, professional air sampling is protective of your health — it provides objective evidence of air quality conditions that can inform decisions about whether the space is suitable for occupation.

Book a Professional Mould Assessment

Request a Free Quote — we’ll discuss your situation and recommend the right combination of assessment methods. We cover all of Northern Rivers with inspections typically scheduled within 24 hours.