Surface mould

Start here

Mould on walls, ceilings and window frames in UK homes is almost always a condensation symptom: warm, moist air meeting a cold surface until the surface stays damp enough for spores to grow. Building standards use about 80 per cent humidity at the surface, sustained, as the risk threshold. That is why it appears in the same places every winter: behind wardrobes on outside walls, the top corners of bedrooms, bathroom ceilings and the bottom of window frames. Cleaning removes what you can see. Only fixing the moisture stops it returning; Oxford City Council puts it plainly: removing mould will not solve the problem if excess moisture remains.

Two rules run through every guide here. First, small patches on hard surfaces are a reasonable job for most households, using a mould and mildew product as its label says, with gloves, mask and goggles, wiping when wet and binning the cloth; GOV.UK prefers these products to bleach for health and safety reasons. Second, larger areas, mould that keeps returning, soft plaster, textured ceilings in pre-2000 homes and any home where someone is in a higher-risk group (GOV.UK lists people with lung and heart conditions, weakened immune systems, pregnant women, children and older people among them) are for a professional and, if you rent, the landlord. Never mix cleaning products, and never use one after another on the same patch.

Which guide do you need?

Before you clean anything

• Size. GOV.UK says tenants could reasonably be expected to remove condensation and very small amounts of mould; larger areas are for qualified professionals. Retailers commonly use “under one square metre” as a rule of thumb.
• Who is in the home. If anyone is in a higher-risk group, do not clean it yourself with them in the room, and report it rather than manage it.
• The surface. Hard painted plaster, tiles and uPVC clean well. Soft or crumbling plaster, wallpaper that lifts, bare timber and textured coatings in pre-2000 homes need a different route; HSE warns that textured coatings may contain asbestos and must not be sanded or scraped.
• The product. One purpose-made mould and mildew product, used as its label says. For large areas Oxford City Council points to a fungicidal wash with an HSE approval number. Do not brush or vacuum dry mould; it releases spores.
• Bleach. It can work on non-porous surfaces such as tiles and glass and it lightens stains, but GOV.UK prefers mould products for health and safety reasons, and on porous walls bleach tends to whiten the mark while growth in the surface survives.

Why it comes back

Mould returns because the surface is still cold and the air is still wet. The condensation hub covers the three levers: less moisture, more ventilation, steadier warmth. The two fixes that matter most in practice are running the bathroom extractor fan for at least 15 minutes after a shower (Energy Saving Trust) and leaving a gap between furniture and outside walls so air can move. Anti-mould paint is for after the cause is fixed, on a cleaned and dry surface; Oxford City Council says never to paint or paper over untreated mould.

Coming next in this topic

Guides in preparation: mould in or behind a wardrobe, mould out of clothes and fabric, and mould in the bathroom (a room-by-room prevention plan). Added as sources are checked; no fixed dates. Black mould on silicone now has its own guide in the silicone and grout topic, and peeling paint over mould is covered under paint and moisture-damaged surfaces.