Problems
Why damp and mould keep coming back
Written by Martin, M24/7 Bathrooms
Last updated:
How to tell condensation from a leak, and what to fix before decorating again.
Repainting a mouldy bathroom wall is the most commonly repeated mistake in home maintenance. The mould returns because the cause was never addressed, only covered.
This guide explains how to distinguish condensation from a leak or moisture entering from elsewhere, so the cause can be addressed before bathroom finishes are renewed.
Condensation, the usual culprit
Warm wet air meets a cold surface and water forms. It shows as black spotted mould in corners, on cold external walls, around window reveals and on ceilings. It is worst in winter and in rooms with no working extraction.
Leaks behind tiles
A failed seal at a shower tray or a pinhole on a pipe produces damp in one localised area that does not improve with ventilation. Grout going dark in a single patch, or a stain on the ceiling below, is the usual first sign.
Moisture entering from elsewhere
A low tide mark, salts on plaster or a patch that worsens after rain points away from bathroom condensation. The source needs to be identified and resolved before bathroom surfaces are repaired or covered.
How to tell them apart
A rough diagnostic before anyone opens a wall.
- Black spots in corners and on cold walls: condensation
- One localised damp patch near a shower or pipe: leak
- Tide mark low on the wall with salting: rising damp
- Damp worsening after heavy rain on one elevation: penetrating damp
- Damp only in winter: almost certainly condensation
Fixing it properly
Condensation needs extraction that actually clears the room, plus warmer surfaces. Leaks need the seal or pipe repaired and the substrate dried. Moisture entering from elsewhere needs its source resolved before replastering or bathroom finishes begin.
Only then is it worth decorating, and only then will tiles stay put.
Want a professional to handle it?
Get a quote from M24/7 Bathrooms.
Questions
Frequently asked
Will mould resistant paint solve it?
It slows the symptom. If the wall is still cold and wet, the mould returns.
Is an extractor fan enough on its own?
Often yes for condensation, provided it is the right size, vented outside and left running long enough after showering.
Should damp be treated before a new bathroom?
Always. Treating it first is far cheaper than taking a finished bathroom back apart.
Should moisture problems be resolved before a renovation?
Yes. The source should be identified and resolved before new plaster, decoration or bathroom finishes are installed.
Why does my bathroom only go mouldy in winter?
Cold surfaces. That is condensation rather than a leak, and the fix is ventilation and insulation.