Damp walls: finding and fixing the problem

There are numerous causes of damp walls. But, before tackling dampness in your home, make sure you're going after the actual cause — otherwise you might make things worse. Here's a helpful guide to finding and fixing some common problems that cause damp walls.

• If you have damp patches, bubbling paint, crumbling plaster or powdery deposits on wall surfaces close to the floor, rising damp is probably the culprit.
• Rising damp usually occurs in masonry walls because of the failure or absence of a damp-proof course, although poor sub-floor ventilation and bad site drainage can also contribute to the problem.

• Improve the drainage of the site. Make sure the surrounding ground slopes away from your home.
• Check that there's enough room under the floorboards for moisture to evaporate from the soil below and pass out through sub-floor wall vents.
• Install a damp-proof course.
• Installing a damp-proof course is best left to the professionals.

• If you're not sure of the cause of a damp patch on a wall, try the foil test.
• Dry the wall surface with a fan heater, then tape some aluminum foil tightly over the affected area.
• If the surface of the foil is wet after 24 hours, you have condensation to blame for the dampness.
• Condensation occurs when moisture-laden air builds up inside your house.
• Poor ventilation and overly efficient draft-proofing are often to blame.

• Install extractor fans or vents in kitchens, laundries and bathrooms so that moist air is expelled outside the house before it causes problems inside.
• Don't use moisture-producing portable gas heaters that are without flues to warm cold, damp rooms.

• Damp patches on walls are generally the result of penetrating damp, where water from outside gets into the brickwork through gaps and cracks.
• If the patches are clustered around windows and doors, then it's likely that rain is getting in through gaps around the frames.
• If the damp is below the opening, it may be because there is no drip groove below a projecting sill.
• Faults in the brickwork, including cracked pointing, are most likely the causes of any other patches of damp.

• Keep external walls, including the pointing and the paintwork, in good condition.
• Seal the gaps around window and door frames.
• Clear out or cut drip grooves below windowsills.

• Faults in your roof structure, including damaged or missing tiles, poor flashing and broken or cracked gutters and downpipes, can be the cause of dampness in your house.
• Dampness due to leaks is usually easy to spot, since it's generally located around either the ceiling or on sections of wall that line up with the external pipework.
• Damp patches may also be the result of leaks in plumbing work embedded in the wall or from poorly sealed bathrooms.

• Repair a faulty roof.
• Deal with leaky pipes.

Keep this helpful guide in mind to get a start on properly finding and fixing the problems behind your damp walls.