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Rising Damp

Rising damp is caused by capillary suction of the fine pores or voids that occur in all masonry materials. The capillaries draw water from the soils beneath a building against the force of gravity, leading to damp zones at the base of walls.

There are various reasons buildings are effected by rising damp. The most common causes in the U.K. are dpc (damp proof course) failure, bridging due to the raising of external ground or internal floor levels, or in older buildings, the complete absence of a dpc.
Most building materials are porous allowing damp from the ground to
rise by capillary action. Brick, stone and mortar are particularly
susceptible to this form of absorption although levels of porosity vary.

This phenomenon also has the characteristic of carrying with it ground
salts including chlorides and nitrates. These salts are hygroscopic and
have the ability to absorb moisture from the atmosphere leading to wall
dampness in conditions of high relative humidity. In addition their
cyclical nature of crystallisation and rewetting causing internal decorations to become discoloured, plasterwork will crumble and skirting boards decay. Wet rot and dry rot can also be caused by rising damp.

Rising Damp Treatment

Remedial treatment for rising damp involves removing the defective plaster and skirting boards, installing a new chemical damp proof course, apply a sand & cement backing of 3:1 sand/cement
with waterproof & salt inhibiter additive min. 12mm thick, multi finish plaster - 3mm thick and re-fitting the original skirting boards or fitting new ones depending on condition.