Typical signs
- Black, green, grey or white spotting on materials.
- Persistent basement, wet cardboard or earthy odour.
- A surface that stains again after cleaning.
Where it is often found
- Basements, window reveals, behind furniture on cold walls, under sinks, around showers and near roof/leak areas.
What it can mean
- Leak, intrusion, condensation or chronic humidity.
- Poor ventilation, thermal bridging or a porous material that remained wet.
What to check next
- Find and correct the water source before cleaning.
- Determine visible and hidden extent.
- Assess whether the material should be replaced instead of cleaned.
Reasonable immediate actions
- Limit dust spread; avoid dry brushing.
- Protect sensitive occupants and dry the area quickly.
When to stop and call a professional
- Large area, contamination inside a cavity, strong odour without a clear source, mould in HVAC or vulnerable occupants in the home.
Prevention
- Control humidity, ventilate, maintain seals and repair leaks quickly.