Rising damp is moisture that travels upward through masonry from the ground by capillary action. It occurs in walls that lack an effective damp proof course, or where an existing damp proof course has failed or been bridged. Rising damp is most common in older properties, particularly Victorian and Edwardian buildings that were constructed before damp proof courses became standard practice.
The most common signs of rising damp include tide marks on lower sections of walls, peeling paint and wallpaper, white salt deposits on plaster known as efflorescence, damp or wet patches on lower walls and a distinctive musty smell. Rising damp rarely rises above one metre from floor level.
The standard treatment for rising damp involves injecting a silicone-based chemical damp proof course into a continuous line of holes drilled into the mortar course at the base of the wall. The silicone material lines the pores of the masonry and prevents further moisture movement. Salt-contaminated plaster is removed and replaced with a specialist waterproof rendering system and final skim coat.
A professional rising damp survey uses calibrated moisture meters to measure moisture levels in walls at various heights. Surveyors also check for salt contamination, assess the condition of existing damp proof courses and look for contributory factors such as bridged cavities and high external ground levels.
The cost of treating rising damp depends on the length of affected wall and the additional works required. A typical rising damp treatment for a terraced house costs between 500 and 1500 pounds. This includes damp proof course injection, plaster removal and specialist replastering. Free surveys are available in most UK locations.