The short answer
Check what is still wet, not just what looks mouldy. Plasterboard, insulation, carpet underlay, joinery and wall frames hold water long after surfaces dry, and that is where mould starts. Map moisture before rebuilding, and don't close up walls over materials that haven't dried.
Queensland Health’s key advice
Queensland Health’s Mould after a disaster fact sheet sets out the basics for households:
- Dry the home quickly — open doors and windows.
- Carpets waterlogged for more than two days may need to be thrown out.
- Don’t dry-brush mould — it releases spores into the air.
- Bleach may not work on porous surfaces, and should never be mixed with vinegar.
- Protect yourself with rubber gloves, safety goggles, a P2 face mask, protective clothing and enclosed footwear.
- See your doctor if anyone in the household has health effects from mould.
What stays wet
Floodwater wicks upwards through porous materials, often well above the visible water line.
| Material | Typical behaviour |
|---|---|
| Plasterboard | Wicks water up; paper face supports mould; soft to the touch when wet |
| Wall insulation | Holds water for a long time and slows drying of the frame |
| Carpet and underlay | Underlay stays wet beneath a dry-feeling carpet |
| Particleboard joinery | Swells and rarely recovers |
| Timber frames and floors | Dry slowly; need readings to confirm |
| Concrete slab | Can take weeks to dry through |
When to test
Early: moisture mapping as soon as it is safe to go in shows how far water has travelled and gives drying contractors a baseline.
Before rebuilding: check frames, slab and subfloor are back to dry readings before new linings, flooring or joinery go in. Sealing wet framing inside new plasterboard is one of the most common causes of mould appearing months after a repair.
After drying and any mould works: an independent clearance check — visual, moisture and air samples compared with outdoors — confirms the house is ready to live in.
Keep a record
For insurance, keep dated photos of the water line, damaged items before they are thrown out, and any moisture readings. An independent inspection report pulls these together in one place.
Questions people ask
How quickly does mould grow after a flood?
It can start within days in warm, humid conditions on wet porous materials. That is why Queensland Health stresses drying the home out quickly.
Is it safe to stay in a flood-affected home with mould?
That depends on the extent and the people living there. People with asthma, allergies, lung disease or weakened immunity are more likely to be affected. Ask your GP, and follow Queensland Health's protective advice when handling mouldy materials.
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.