Damp and mould.

Damp means unwanted moisture. Mould is a fungus that can grow where materials stay damp..

01 / SPOT THE PATTERN

Where does damp and mould appear?

Record what you see before cleaning. Patterns are clues; the same mark can have different causes.

02 / UNDERSTAND THE MOISTURE

Four routes to a damp home.

Condensation: water from the air

Think of a cold drink misting up. Moist air touching a cold enough surface leaves water behind. Cooking, bathing and breathing all add moisture. A home needs a way to remove it. Cold walls, weak extraction and inadequate heating can combine to create the problem. It is not simply a sign of poor housekeeping.

Penetrating damp: rain getting in

Rain can enter through a damaged roof, leaking gutter, cracked wall or failed window detail. A patch that grows after rain is an important clue. Wind direction may matter too.

Leaks: water escaping indoors

Supply pipes, wastes, heating pipes and shower seals can leak into walls or floors. Some leaks are hidden and continue even in dry weather.

Ground moisture: water entering at low level

Rising damp is ground moisture drawn up through porous walls. Moisture can also enter floors in contact with the ground. Raised soil or paving can also bridge a damp-proof barrier. Check these possibilities alongside drains, plumbing and condensation before choosing treatment.

03 / ASSESS BEFORE BUYING A TREATMENT

Start with evidence, not a quick sales pitch.

1. Make a simple record. Photograph the patch, note the room, date and approximate size. Does it follow rain, showers or cold mornings? Has anything changed, such as new windows or insulation?
2. Look safely inside and outside. From ground level, check gutters, downpipes and visible roof or wall defects. Indoors, check accessible pipework, sealant, heating and fans. Do not climb onto a roof or open electrical equipment.
3. Check how the home handles moisture. Are extract fans working and discharging outdoors? Are vents clear? A recirculating cooker hood filters cooking smells but does not send the moisture outside.
4. Use measurements as clues. A room humidity monitor shows moisture in the air; a surface thermometer helps locate cold spots. Log readings over time. One reading cannot identify the source of a leak or diagnose a wall.
5. Ask for a reasoned survey where the cause is unclear. The report should explain likely causes, evidence, limits of inspection and repairs, with further tests where needed.

A damp meter is not a diagnosis. Electrical readings on plaster or masonry can be affected by salts and other materials. A high reading alone does not prove rising damp or justify chemical injection. Ask how the reading fits the building and the other evidence.

Further reading: PCA investigation and control of dampness code.

04 / CLEAN SAFELY

Removing mould without spreading the problem.

For a very small patch on a washable hard surface, cleaning may be manageable if you are well enough and can follow the product instructions. If you are unsure, ask a competent mould-removal professional. Do not wait for major repairs to be finished before arranging safe mould removal.

1. Photograph the area. Keep other people away, close internal doors and ventilate the room to outside.
2. Wear suitable gloves, eye protection and respiratory protection appropriate to the task and cleaner. Follow the product’s safety instructions.
3. Use an appropriate mould-and-mildew cleaner on suitable surfaces, following its label and contact time. Never mix cleaning products, especially bleach with other cleaners.
4. Avoid dry brushing, sanding or disturbing mouldy wallpaper. Wipe carefully, deal safely with used cloths and waste, and allow the surface to dry completely.
5. Mouldy absorbent materials, such as carpet, insulation or plasterboard, may need professional removal and replacement. Surface wiping may not reach the growth inside.

Do not paint over active mould or wet materials. Anti-mould paint is a finishing product, not a repair for a leak, cold wall or failed ventilation. A clean-looking surface does not prove the moisture problem has gone.

Further reading: EPA guidance on mould cleanup.

Further reading: UK guidance on safe removal.

05 / REPAIR THE CAUSE

The right fix depends on the source.

A dehumidifier can help remove moisture from the air while a problem is being managed. It cannot repair a leak or replace a suitable ventilation system. If heating costs are a barrier, seek support rather than accepting a persistently damp home.

Understand ventilation · Explore insulation · Find funding and support

06 / CHECK THE RESULT

Has it actually been solved?

Keep dated photographs and compare the same places after wet weather and during colder periods. Check that repairs are complete, fans work and surfaces are drying. Revisit the problem after a few weeks and through the conditions that originally caused it.

If staining, moisture, mould or a musty smell returns, reopen the investigation. Do not keep paying to repaint the same patch. The original diagnosis may be incomplete, or there may be a second source.

Common questions