Donate SIGN UP

What, apart from a hit 1970's sitcom, is rising damp

01:00 Fri 18th Jan 2002 |

A. Rising damp is caused when water from the ground spreads into the brickwork by means of capillary action, i.e. rising through fine cracks in the masonry. It is usually found only in the first metre or so of the wall.

Q.� How common a problem is it

A.� It is actually quite rare. Since 1875 all new houses built were installed with a damp course, essentially a membrane, basically a waterproof barrier built into the walls to prevent the problem.

Actually rising damp is often misdiagnosed by either unscrupulous or inexperienced builders. The vast majority of problems that are mistaken by for rising damp are caused by things like leaking guttering, faulty or leaking plumbing, condensation caused by inadequate ventilation (the average family produces 50 litres of liquid vapour just by breathing every evening) or by people raising the ground level outside against an exterior wall by building a patio or creating a raised flowerbed.

Q.� So only houses built before 1875 will get rising damp

A.� Not quite. rising damp can affect any property, however well treated, if the damp protection is 'bridged'.

This essentially means that some sort of structural change like extending the plaster work too far down a wall or building that patio outside has created a route for moisture to penetrate the walls while circumnavigating the damp course.

Q.� What are the tell-tale signs

A.� Rising damp will almost always mean damp patches and stains up to about 1 metre up the wall. Only if it has been allowed to go unchecked will it have spread higher up.

To be sure you need to look at the exposed surface of the brick and check to see if there are salts forming, that the brick is actually wet (not just the wallpaper or paint) that there is no mould present and if the skirting board is showing signs of rot.

Q.� If we establish it definitely is rising damp how do we treat it

A.� The common treatment is to install a damp proofing course.

This generally involves stripping away the sodden skirting board and plaster to about a metre to expose the brick. Holes are then drilled and a silicone-based chemical is injected into the brickwork. The chemical seeps through the brick and the mortar and forms an new barrier to damp. When that is done the wall is re-plastered with sand and cement containing a waterproof additive.

If it is an external feature like the patio or flowerbed that is to blame the damp can be cured by lowering it below the level of the original damp course and then allowing the area to dry out naturally by opening windows and heating the room.

Q.� Who should we get in to do it

A.� There are thousands of damp coursing firms out there. Like any major structural work to your house it is worth getting at least two or three quotes before you commit to the work.

Whoever you chose make sure they offer a guarantee, usually 20 years, which is backed by the professional association The British Wood Preserving and Damp-proofing Association (BWPDA). For a list of members in your area call them on 01332 225 100.

If you've got a question about your home or garden, click here.

By Tom Gard

Do you have a question about Home & Garden?