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 does break 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 often 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.
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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.
