Rising dampness is where dampness rises up through the walls (both external and internal) of a building, by natural capillary action. In modern buildings (post 1950), this defect is prevented by the use of effective damp proof courses built into the base of the walls. However in older buildings, a horizontal layer of slate was used instead. With age, slate becomes porous (after approximately one hundred years), which allows dampness to rise up in the wall. This dampness can then cause rot/decay to nearby floor and other timbers and damage plastered wall surfaces. This defect is usually remedied by drilling a series of holes to the base of the affected wall/s and pressure impregnating the wall with a silicon solution, which then sets to provide a horizontal waterproof barrier. The damp affected internal plaster is removed and replaced with a special plaster. An inspection of any damp affected floor or other timbers should also be carried out at the same time, as it may be necessary to treat or repair/replace any timbers affected by rot/decay. While this method of remedying rising dampness defects is widely used and is accepted by most mortgage lenders, it is not always successful and much depends on the quality of the workmanship.