Damp / mould / condensation / damp
What should I do about a damp wall?
Start with the observable symptom. This page explains possible causes; it is not a diagnosis. It covers both “mould” and “mold” wording for the same intent.
A damp wall is a symptom, not a diagnosis. Check whether moisture follows condensation, a leak, rain or a rising pattern, then stop cosmetic repairs until the source has been assessed.
Start with the pattern.
A wall has a wet-feeling patch, stain, tide mark, mould, peeling finish or a musty smell.
Possible causes, not a diagnosis.
- Condensation is forming on a cold internal surface.
- Water is penetrating from outside or escaping from plumbing or heating pipework.
- Moisture may be rising from below, although that should be professionally assessed rather than assumed.
Check what is safe to observe.
- 01
Record the height, shape and location of the patch and whether it changes after rain.
- 02
Look on the other side of the wall and around nearby pipes, windows and gutters.
- 03
Check for mould, salts, bubbling paint, soft plaster or a surface temperature difference.
Take the smallest useful step.
- Keep the area ventilated and avoid trapping moisture under coverings.
- Photograph and date the damage before cleaning or decorating.
- Report leaks and damp promptly if you rent.
- Do not buy a damp-proof treatment based only on an online diagnosis.
- Do not drill, seal or repaint the wall before the cause is understood.
- Use a qualified damp surveyor or building professional for a persistent or spreading patch.
- Get urgent help for active leaks, structural movement or water near electrics.
Professional requirements and rental responsibilities vary by location. Use the qualified local professional or housing authority that applies where you live.
UK example: GOV.UK repairs guidanceWhy this page says that.
This page separates an observable symptom from possible causes and keeps the recommended action within a safe household boundary.