The essentials in 30 seconds
Mould grows where moisture meets cold surfaces: window frames, wall corners, behind furniture and in bathrooms. The most common cause is condensation from everyday life: cooking, showers and drying clothes indoors. To remove small patches, wear gloves, goggles and a mask, open the window, clean with a mould and mildew product or detergent and water, and dry the surface completely. Then tackle the moisture: ventilate, run extractor fans, keep humidity below 60 % and leave a gap behind furniture. Larger areas, mould that keeps coming back or signs of leaks or structural damp need a professional.
- Cleaning alone does not stop mould returning: the moisture source needs fixing.
- Avoid painting over mould: clean and dry first, then use a mould-resistant paint.
- Babies, older people and anyone with asthma, allergies or a weak immune system are most at risk.
Why mould grows on walls
| Type | What causes it | Typical clues |
|---|---|---|
| Condensation | Moisture from cooking, showers and drying clothes settling on cold surfaces | Black spots in corners, on window frames and behind furniture; worse in winter |
| Penetrating damp | Water entering through walls, roofs, windows or gutters | Patches that grow after rain, often on outside walls or ceilings |
| Rising damp | Ground moisture rising through walls in older buildings | A tide mark low on the wall, salts, crumbling plaster; often misdiagnosed |
| Leaks | Pipes, overflowing baths or sinks, burst pipes | A patch below a bathroom, kitchen or pipe run |
Condensation is by far the most common cause. If the patch grows after rain, sits low on the wall with salt marks or appears below a bathroom, look for the water source first.
What you need before you start
- Rubber gloves reaching the middle of the forearm.
- Goggles without ventilation holes.
- A well-fitting FFP2 or N95 mask.
- A mould and mildew cleaning product, or detergent and warm water.
- Disposable cloths and a bin bag.
- A dry cloth or towel.
How to remove mould from a wall step by step
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01
Photograph it first
Photos help a surveyor or landlord identify the source later.
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02
Ventilate the room
Open the window and close the internal door to keep spores in the room.
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03
Protect yourself
Gloves, goggles and mask on before you touch the mould.
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04
Clean gently
Apply the mould product as the label says, or scrub hard surfaces with detergent and water. Avoid dry brushing, which spreads spores.
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05
Dry completely
Wipe the area dry and keep the window open for a while.
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06
Bag the waste
Put cloths in a sealed bag straight away and wash your clothes afterwards.
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07
Deal with soft items
Mouldy carpets, soft furnishings or ceiling tiles may need to be thrown away if the mould cannot be removed.
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08
Fix the moisture
Follow the prevention steps below, or the mould will be back within weeks.
Painting a wall that has had mould
Wait until the wall is clean and completely dry. Painting or caulking over mould traps it: the paint will peel and the mould will come back. Once the moisture problem is solved, an anti-mould paint in bathrooms, kitchens and cold corners helps keep surfaces clean.
How to stop mould coming back
- Ventilate: open windows wide for a few minutes after cooking or showering, and keep trickle vents open.
- Use extractor fans: check they work; humidity-controlled fans or fans that keep running after the light goes off are ideal.
- Cover pans when cooking and close internal doors while cooking or showering.
- Dry laundry outdoors when you can; if not, in a ventilated room or with a dehumidifier.
- Keep humidity below 60 %, ideally 30–50 %. A cheap hygrometer tells you where you are.
- Leave a gap between furniture and outside walls.
- Keep the home evenly warm in winter: cold walls condense more. Good insulation helps, as long as ventilation is kept.
Common mistakes
- Scrubbing dry mould, which sends spores into the air.
- Painting over mould without cleaning and drying.
- Blocking vents and trickle vents to keep heat in.
- Treating the mould and ignoring a leak, a blocked gutter or a failed damp-proof course.
When to call a professional
- The mouldy area is larger than about 1 m², or keeps coming back.
- Patches grow after rain or sit low on the walls with salt marks.
- You smell mould but cannot see it: it may be behind panels, under flooring or in ventilation.
- Someone at home has asthma, a lung condition or a weak immune system.
A damp surveyor can find the cause. If you rent, tell your landlord in writing and include your photos.
Black mould: frequently asked questions
Is black mould dangerous?
It mainly affects the airways and lungs and can make asthma and allergies worse. Babies, older people and anyone with a lung condition are most at risk.
What kills mould on walls?
A mould and mildew product, or detergent and water on hard surfaces, then drying completely. The moisture source must be fixed too.
Why does mould keep coming back?
Because the moisture is still there: usually condensation, sometimes a leak or structural damp.
Can I paint over mould?
Not until it is cleaned and the wall is completely dry. Then use an anti-mould paint.
What humidity stops mould?
Keeping indoor humidity below 60 %, ideally between 30 % and 50 %.
Who should deal with mould in a rented home?
In the UK, landlords are responsible for finding and fixing the underlying cause. Report it in writing with photos.
Sources
Official health and housing guidance, checked on 24 October 2026.
- GOV.UK · Understanding and addressing the health risks of damp and mould in the home ↗Types of damp, who is most at risk, reducing condensation and removing surface mould.
- US EPA · A brief guide to mold, moisture and your home ↗Humidity below 60 %, cleaning hard surfaces, protective equipment and not painting over mould.
- WHO · Guidelines for indoor air quality: dampness and mould ↗Health effects of damp indoors.
Mould keeps coming back?
Measure the humidity for a week and take photos of every patch before calling a damp surveyor.