Quick answer: Mould keeps returning because the spore load in the surface wasn't adequately removed, the moisture source wasn't fixed, or both — wiping visible mould leaves the hyphae root system embedded in the surface, and the mould regrows from it, often faster than the original growth. Surface treatment alone is not sufficient if mould has grown on plasterboard for a prolonged period — the correct approach is to remove and replace the affected section using a contractor with H-Class extraction to contain spores during strip-out.
If you've cleaned mould off a wall and it's come back — possibly within a few weeks — you're not alone and you haven't done anything wrong. Recurring mould is one of the most common complaints in UK homes, and it almost always has the same underlying explanation: the visible mould was removed but the spore load in the surface wasn't, the moisture source wasn't fixed, or both.
Why mould comes back
The spore load in the surface wasn't removed. Mould has a root system — called hyphae — that penetrates into the surface it's growing on. When you wipe or spray the visible growth, you remove what you can see but leave the hyphae embedded in the plaster, paint or grout. Effective removal requires a biocidal product that kills the mould at the root, not just removes the surface appearance. Apply it, leave to dwell for the time specified, then wipe. A second application a few days later on stubborn patches improves results significantly.
The moisture source hasn't been fixed. Mould grows where moisture is present. If the conditions that allowed mould to establish haven't changed, the mould will come back regardless of how thoroughly you clean it.
The affected material needs replacing, not treating. On plasterboard, porous plaster or timber with significant mould growth, surface treatment doesn't reach deep enough into the material to remove the spore load. The correct approach is to remove and replace the affected section rather than treat the surface — using a contractor with H-Class extraction (rated to 99.995% with sealed disposal) to contain spores during strip-out. Standard vacuums used on mould remediation spread spores rather than containing them.
What the law says
Recurring mould is not a successfully resolved repair. Under the Homes (Fitness for Human Habitation) Act 2018, the property must be maintained in a fit condition throughout the tenancy. Under Awaab's Law, a repair that results in mould returning within weeks is not a completed repair. Under the Renting Homes (Wales) Act 2016, recurring mould is ongoing non-compliance with the fitness standard, not a series of separate incidents.
What you can do now
Identify and address the moisture source first. Use a biocidal mould spray or wash with at least 15–20 minutes dwell time. Improve ventilation consistently — use extractor fans, ventilate rooms daily, keep trickle vents on windows open. If mould is in plasterboard that keeps returning despite surface treatment, the material needs to come out with a contractor using H-Class extraction. If you rent and your landlord's treatment hasn't resolved recurring mould, put this in writing and request the underlying moisture source is investigated and fixed. Keep a photographic record of each recurrence with dates.
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