Damp Proofing

Rising damp refers to the natural process of dampness in the ground rising up through the structure of a building. The purpose of a damp proof course is to prevent this process by establishing a horizontal barrier sited near the base of a property which prevents the passage of moisture.

Damp proof courses are included in new buildings but this was not always the case with older ones. A damp proof course breaks down over a number of years and eventually needs replacing. Properties over 80 years old are particularly at risk of rising damp

As a damp proof course fails, damage occurs to lower wall areas. This includes disruption to plaster and decay affecting timbers in contact with the damp walls. Early signs of a damp problem may include discolouration of decorations on wall surfaces.

Rising damp brings with it destructive nitrate and chloride salts from the ground. These salts are often hygroscopic in nature. At times of high humidity the salts absorb moisture from the air adding to the overall damp problem.

The solution to rising damp in an existing property is a remedial damp proof course. This process involves removing the affected plaster and skirting boards, installing a new chemical damp proof course, re- plastering with salt resistant plaster and renewing the skirting boards. Existing skirting boards may be retained if they are in good condition.

Treatment can be carried out to individual walls or full properties. In recent years chemical damp proofing has gone through something of a revolution with a movement away from solvent- based injection fluids installed using high – pressure pumps to water- based creams installed using low- pressure cartridge guns.

Another main cause of damp is penetrative damp. This is where dampness enters a building laterally through the walls. This most often occurs when there is a building fault, such as a broken gutter or drainpipe, which causes water to pool against the exterior of the building and consequently seep through to the interior. Another main cause of penetrative damp is via an earth retaining wall (that is to say a wall whose exterior is below the level of the ground such as a basement or a building built into a slope).

Although the method of entry for penetrative damp differs to that of rising damp, the results are the same; stained decoration, mould and mildew, rotten skirting’s and woodwork, salt crystallization on walls, crumbling plaster and that overpowering mouldy stench of decay. Condensation problems are another leading cause of issues with dampness.

However, unlike rising and penetrative damp, condensation can be more easily dealt with. Condensation occurs when warm moist air meets a cold surface and the most common causes of condensation in domestic situations are bad ventilation and fluctuating temperatures. One of the worst culprits for condensation is gas fires, in particular the old style portable gas heaters.