Dealing with damp problems
Damp can be divided into rising damp and penetrating damp. Moisture from the air inside the house condensing on surfaces can also cause mould growth.
This is caused by moisture in the ground penetrating the lower levels of a house. Normally, a waterproof layer between the lower levels of bricks or blocks, called a damp-proof course, stops any moisture rising up the walls. A sheet of waterproof material, the damp-proof membrane, does the same job for any solid floors.
Older houses may not have a damp-proof course or it may have broken or breached - in which case, call in a specialist firm who can guarantee their work.
Rising damp may be caused by soil building up against the outside wall above the damp course. If the soil next to your house is less than 150mm (6in) below the level of the course, dig it away and let the wall dry out. If this doesn't work call in a professional damp treatment company.
Any water that finds its way from the outside of your house to the inside is classed as penetrating damp. This is usually a problem restricted to older homes build with solid walls.
You can often cure penetrating damp yourself if you can find the cause. If you find dark damp patches or mould growth on an interior wall, check on the outside of the house: the roof may have some missing or broken tiles or the lead flashing around a chimney may be damaged. Call in a roofing company to make the repair.
If you see isolated patches on a wall, check that gutters or downpipes aren't blocked or cracked, causing water to seep into the wall. The problem could also be the result of damaged render, badly weathered pointing or damaged brickwork. Repair as required.
Damp around windows and doors
If you see damp around a window, check the small round groove on the underside of the window sill isn't blocked, as it's there to stop rainwater seeping into the wall under the window. Unblock the groove or fit a new sill if rotten. Check for gaps between the window frame and the wall and seal with a flexible exterior mastic. If you have damp around a door, there may be a gap around the door frame and the exterior wall. This is easily sealed with a flexible exterior mastic. Also, check the sloped weatherboard at the bottom of the door isn't rotten.
For more information, see the British Wood Preserving and Damp-Proofing Association.