Rising damp (structural)

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Rising damp is a condition caused by ground moisture rising up a masonry wall by capillary action. It occurs where there is no damp-proof course (DPC) or where the DPC has been damaged or bridged. Where present, moisture can rise up the wall to a height of a metre and it will often leave a characteristic horizontal 'tide mark'.

[edit] Symptoms

Rising damp tends to cause secondary damage to a building. The unwanted moisture enables the growth of various fungi in wood, causing rot. Plaster and paint deteriorate and wallpaper loosens. Stains, from the water, salts and from mold, mar surfaces. Externally, mortar may crumble and salt stains may appear on the walls. Steel & iron fasteners rust. It may also cause respiratory illness in occupants. In extreme cases, mortar or plaster may fall away from the affected wall.

[edit] Prevention

Well built modern houses include a synthetic damp-proof course (DPC), about 15cm above ground level, to act as a barrier through which water cannot pass. Therefore the problem is mainly related to older structures, where no water proof barrier was utilised, or where ill designed building modifications have been performed. However, slate or "engineering bricks" with a low porosity were often used for the first few courses above ground level, and these can minimise the problem.

[edit] Treatment

Effective treatment is a specialized job and is expensive and labour intensive. The cause of the damp must first be eliminated, by installing a physical or chemical DPC. Then, any affected plaster or mortar must be removed, and the wall treated with a solution of acetic acid, before replacing the plaster and repainting. The major Rising damp treatment authorities within the U.K. are The British Wood Preserving and Damp-proofing Association (BWPDA) and The Property Care Association.