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Damp-proof course / Electro-osmosis / French drain / Air drain

- (Dpc) An impervious layer built into a wall a little above the surface of the ground in order to prevent moisture rising up the wall by capillary attraction, the process known as rising damp. Also used below cills above lintels and at wallheads to prevent water penetration. Rising damp is a complaint which usually affects older property, damp proof courses became compulsory in Britain in 1875. Dpc's are usually bitumen, but can be slate or on occasion lead, in older buildings.

Damp, can be a problem in old buildings, but solutions to rising damp can often lie in simply reducing ground level, common sense should always prevail. The most straightforward approach is to investigate if it is possible to saw through a bed to insert a dpc in stages. Gravity feed of waterproofing chemical is currently popular but can lead to unsightly row of holes if nobody takes the trouble to insist on work being done from inside. Also, it can take an awful lot of fluid to form a barrier in a large porous core. The fluid should never be pumped, but always gravity fed.

Electro-osmosis, a strange system of earthed wires which were secured to the base of buildings, working on the potential difference between natural electric charge, was used at one time, mainly during the 1970's. It appeared to work but was vulnerable to mechanical damage.

A french drain is a trench filled with gravel, stone, tile etc. They can be used to collect ground water and deflect it away from buildings, and are therefore often found where buildings are built into sloping ground.

Air drains, found at a number of great houses, are chambers, which can be lined in brick or stone slab which collect water, which then evaporates off. Harder stones or denser bricks are sometimes used at the base of walls in an effort to prevent rising damp.