Black mould: what to know
Black mould on windows, cold corners and external walls commonly accompanies condensation, but recurring mould can also follow leaks, thermal bridging or hidden moisture.
What to check first
- Note whether the surface is visibly wet or simply cold.
- Check whether growth is concentrated behind furniture, around windows or in bathrooms.
- If mould follows rain or sits below a plumbing fixture, investigate that source first.
What not to assume
Cleaning visible mould without reducing the moisture that supports it usually leads to recurrence.
Sensible next step
Deal with the moisture source first, then clean or remediate the affected surface using an approach appropriate to the extent and material.
The clues that matter most
Use several clues together rather than treating one mark, smell or meter reading as proof.
Note whether the surface is visibly wet or simply cold.
Check whether growth is concentrated behind furniture, around windows or in bathrooms.
If mould follows rain or sits below a plumbing fixture, investigate that source first.
Cleaning visible mould without reducing the moisture that supports it usually leads to recurrence.
Deal with the moisture source first, then clean or remediate the affected surface using an approach appropriate to the extent and material.
Could it be something else?
These routes help separate common causes that can create similar visible damage.
Useful products for this stage
Only products that support the investigation or an appropriate fix are shown here. An active leak or building defect still needs repairing.
