What people usually mean by rising damp
Rising damp describes moisture moving upwards through a wall from the ground by capillary action, where there is no effective barrier to stop it. It is generally limited to lower parts of ground floor walls.
Common signs
- A horizontal tide-mark, typically within a metre of floor level
- Blown or crumbling plaster and lifting skirtings
- White, fluffy salt deposits on the wall surface
- Damp that is persistent rather than clearly weather-related
- Decaying skirting boards or floor timbers against the wall
Why similar symptoms can have different causes
Damp at the base of a wall can equally be caused by a leaking pipe under a floor, a path laid above the damp-proof course, water splashing back from a hard surface, a blocked gully, condensation on a cold wall, or cement render trapping moisture in a solid wall.
We do not assume rising damp, and we would rather find you a fifty-pound drainage fix than sell you a treatment you did not need.
Damp-proof course considerations
Most Colchester houses built from the later Victorian period onwards have some form of damp-proof course — slate, bitumen or engineering brick. Older buildings may have none at all, and were designed to manage moisture in other ways. A DPC can also be perfectly sound but bridged by render, plaster, debris or raised ground.
Ground levels and external conditions
- Patios, paths and drives raised above internal floor level
- Soil, planting beds or gravel piled against the wall
- Render carried down over the damp-proof course
- Blocked airbricks restricting subfloor ventilation
- Downpipes and gullies discharging against the base of the wall
Plaster and salts
Where moisture has moved through a wall over a long period, salts can be carried into the plaster. These salts attract moisture from the air, so the wall may continue to appear damp even after the source has been dealt with. This is often why plaster reinstatement forms part of the work.
Investigation and treatment options
Investigation comes first: external inspection, moisture readings, an understanding of the construction and the history of the problem. Where a genuine damp-proof course failure is confirmed, remedial DPC installation with localised replastering may be appropriate. Where it is not, the correct answer is the repair that stops the water arriving.
Not sure whether the signs actually point to rising damp? Start with our free homeowner damp check guide. Read the guide online or download the free PDF.