Quick answer
Persistent mould on a wall is rising damp, condensation, or a slow buried-pipe leak, and the position tells you a lot. Mould confined to the lower metre of an external wall is usually rising damp. Mould in corners, behind furniture and around windows is usually condensation. Mould in a defined patch that keeps returning after cleaning is usually a leak. A moisture meter separates them quickly.
Common causes
- Rising damp where the damp-proof course has failed or been bridged
- Condensation from poor ventilation, worst in bathrooms, kitchens and closed bedrooms
- Slow internal pipe leak feeding one specific area
- Failed external waterproofing or a cracked wall letting driven rain through
- Blocked or missing air bricks preventing a suspended floor from breathing
- Furniture pushed hard against a cold external wall stopping air movement
What you can do now
- 1Note the pattern: low along an external wall, in corners and around windows, or one defined patch
- 2Improve ventilation — extractors in bathroom and kitchen, and open windows after showering
- 3Pull furniture a few centimetres off external walls to let air move behind it
- 4Clean an affected patch, then watch whether it returns in exactly the same shape, which indicates a leak rather than condensation
- 5Check the water meter with everything closed to rule a plumbing leak in or out
When to call a professional
If mould keeps returning in the same place after cleaning and improved ventilation, book a moisture inspection. A plumber can confirm or eliminate a pipe leak with a meter test and detection equipment, which is worth doing before you spend money on damp-proofing — treating rising damp that turns out to be a leaking pipe fixes nothing.
Typical cost in Johannesburg
Inspection R650–R1,200
Indicative ranges only. We provide written, itemised quotes before any work.
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