The short answer
After a flood or leak, mould testing answers two questions: are the walls, floors and subfloor dry yet, and has mould started to grow? Moisture mapping finds the materials that are still wet; air and surface samples show whether growth has begun. The results give your insurer, builder and drying contractor the same documented starting point.
Who books this
- Homes and businesses after floods, storms and roof leaks
- Burst pipes, failed hot water systems and overflowing showers
- Insurance claims that need independent moisture records
Methods used
- Moisture mapping with reference readings
- Thermal imaging
- Air and surface samples
- Dated photographic record
Why speed matters after water gets in
Queensland Health’s advice after a disaster is to dry the home quickly by opening doors and windows, and it notes that carpets that have been waterlogged for more than two days may need to go. Porous materials such as plasterboard, insulation, carpet underlay and particleboard joinery hold water long after the surface feels dry, and that is where mould usually starts.
Queensland Health also warns against dry-brushing mould, which releases spores into the air, and recommends a P2 mask, gloves and eye protection for anyone handling mouldy materials.
Mapping what is still wet
Readings are taken in a grid across affected walls and floors, from the water line upwards and outwards until they reach dry reference values. The result is a marked-up floor plan that shows the extent of wet materials, not just the visible tide mark. Repeating the map later shows whether drying is working.
Testing before walls are closed up
If wall linings have been stripped, the frame and slab can be checked before new linings go on. Sealing a wet frame inside new plasterboard is one of the most common ways a repaired home develops mould a few months later.
Records for an insurance claim
Insurers and loss adjusters work from evidence. A dated report with moisture readings, photographs, sample results and a floor plan is far easier to rely on than a description from memory. Mould Testing QLD only inspects and tests, so the report is independent of whoever carries out the drying or repairs.
Example moisture map
Wall behind a shower, floor to 1.5 m · relative readings
Questions people ask
How soon after a flood should I get a mould test?
Moisture mapping is useful as early as it is safe to enter, because it shows what needs drying. Air and surface sampling is more informative once the property has been dried and before walls are closed up.
Do I need a mould test if I can see mould after a flood?
Visible growth on porous flood-affected materials is usually a decision in itself. Testing is still useful to map how far moisture has spread and to document the property for an insurer.
References
- [1]Mould after a disaster fact sheet — Queensland Health
- [2]WHO guidelines for indoor air quality: dampness and mould (2009) — World Health Organization Regional Office for Europe
Checked against these references on 2 November 2026.