Rising damp is 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 control this process by establishing a horizontal barrier positioned near the base of a building which prevents the passage of moisture.
As a damp proof course fails, damage affects the lower wall areas. Symptoms include disruption to plaster and decay affecting timbers in contact with the damp walls. Early signs of dampness may include discolouration of decorations. Rising damp brings with it destructive nitrate and chloride hygroscopic salts from the ground. At times of high humidity the salts absorb moisture from the air, adding to the damp problem.
The solution to rising damp in an existing building is a remedial damp proof course. This process involves removing the affected plaster and skirting boards, installing a chemical damp proof course, re-plastering with salt resistant plaster and replacing skirting boards.