Black mould on walls: how to remove it and stop it returning

Mould is a living organism that needs one thing to thrive: moisture. In homes that almost always means condensation — moist air settling on cold surfaces like window reveals, the corners of external walls, and behind furniture pushed against cold walls. Clean it off and, if the damp air is still there, it comes straight back.

For most people black mould is an irritant rather than an emergency, but prolonged exposure can aggravate asthma, allergies and breathing problems — and it's a particular risk for babies, older people and anyone with a respiratory condition. The tragic case behind Awaab's Law made the risks of leaving damp and mould untreated very clear. If anyone in the home is affected, treat it as a priority.

For small areas (less than about one square metre):

• Open a window and wear gloves and a mask — don't dry-brush it, as that spreads spores.
• Use a dedicated mould remover, or warm soapy water, and wipe (don't scrub hard) with a damp cloth, then dry the area.
• Bin the cloth afterwards. Soft furnishings with mould may need specialist cleaning or replacing.

For large or repeated growth, or if it's behind plaster, get professional help — and address the moisture, or it will return.

This is the part most people miss. Mould only returns if the damp air does. To break the cycle:

• Ventilate — extractor fans in the kitchen and bathroom, trickle vents open, and a window open when cooking, showering or drying clothes.
• Keep some gentle, even background heat in winter so surfaces don't get cold enough to condense.
• Pull the excess moisture out of the air with a dehumidifier — the single most effective way to hold humidity down so mould can't establish.

If the problem is bad, hiring an industrial dehumidifier for a week or two dries everything out quickly. Find your town for a local hire quote.