Mould analysis and identificationair, surface and bulk samples

Mould is a type of fungus that grows as a network of fine filaments and reproduces by releasing microscopic spores into the air. Mould spores are everywhere, indoors and out, and in normal numbers they are part of the environment we live in. Problems begin when spores land on a damp surface inside a building and find the moisture and food they need to grow.

Building materials are an ideal food source. Plasterboard paper, timber, carpet, fabrics, ceiling tiles, wallpaper paste and household dust all contain the organic material mould digests. Add moisture from a roof leak, a failed shower seal, rising damp, condensation or a flood, and visible growth can appear within days.

The moulds most often found indoors in Australia include Cladosporium, which is also the most common mould outdoors, Penicillium and Aspergillus, which colonise damp building materials and dust, and Stachybotrys, the slow growing dark mould often called black mould, which needs materials to stay wet for an extended period.

Mould is not only a matter of what can be seen. Growth often starts inside wall cavities, under flooring, behind cupboards and inside air conditioning systems, where it can spread for months before anyone notices a stain or a musty smell.

Every mould type produces spores with a characteristic size, shape, colour and surface texture. Aspergillus and Penicillium produce small, round spores in long chains. Cladosporium produces olive brown spores in branching chains. Stachybotrys produces dark, oval spores in sticky clusters that do not become airborne as easily, which is why its presence in the air can be significant even in modest numbers.

Air sampling draws a measured volume of air through a spore trap cassette, which captures particles on a sticky slide. In the laboratory, spores are counted and identified under the microscope, and the result is expressed as spores per cubic metre of air. Surface tape lifts and swabs show what is growing on a specific surface, while bulk samples of plasterboard, carpet or insulation show whether a material itself is colonised.

The single most important comparison in mould analysis is indoor against outdoor. Because outdoor air always contains spores, an indoor result only has meaning when it is read beside an outdoor control collected at the same time. A healthy building usually has indoor levels lower than outdoors, with a similar mix of mould types. Indoor levels well above outdoors, or indoor types that are rare outside, point to a source inside the building.

Moisture is the root cause of every indoor mould problem. Analysis tells you what is there and how much. It is the moisture investigation, and the repair that follows, that stops it coming back.

Australia's climate makes mould a common problem. Humid summers in Queensland and northern New South Wales, cold, poorly ventilated homes in the southern states and repeated flood events have all brought mould to the attention of owners, tenants and insurers.

After major floods, mould can affect thousands of homes at once, and analysis is used to show when a building has dried and been cleaned well enough to reoccupy. In rental properties, mould is a frequent source of disputes between tenants and landlords over whether the cause is a building defect or the way a property is being lived in.

There is no single national numeric standard for acceptable indoor mould levels in Australia. Mould assessment and remediation practice commonly refers to international guidance such as the IICRC S520 standard for professional mould remediation, and results are interpreted by comparison with outdoor controls and the condition of the building.

Mould affects health, damages property and creates financial and legal exposure, often before it is visible.

Cleaning visible mould with bleach may remove the stain without removing the growth in the material below it, and it does nothing about the moisture that caused it. Analysis before and after remediation is the only way to know the problem has actually been solved.

We analyse the full range of mould samples and report results digitally, so assessors, remediators, property managers and home owners can act quickly and with confidence.

Each report identifies the sample type, location, volume of air sampled where relevant, the total spore count and the mould types identified, with indoor results presented beside the outdoor control.

Mould results give remediation companies a map of where growth is, how far it has spread and when the job is genuinely finished.

A successful clearance usually shows indoor levels at or below the outdoor control, with a similar mix of mould types and no growth on the surfaces that were remediated.

Good results start with good sampling. We recommend that mould sampling is carried out by a NATA accredited company, because the right combination of air sampling cassettes, tape lifts, swabs and bulk samples depends on the building and the question being asked.