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Rising damp is the action of water moving vertically through porous building material, which is in contact with the ground. This is brought about by the drying action of air on the upper surfaces which causes the wall to act like a wick, drawing water upwards from the ground by capillary action, which then evaporates from the surface into the atmosphere. The moisture will continue to rise until it reaches a height where, unless evaporation is possible, gravity pulls it down again.
Rising damp occurs because the building’s damp proof course (DPC) has broken down or is being bridged by high ground. A DPC installed during construction will be a physical layer of impermeable material. This can consist of slate, bitumen impregnated felt or plastic, for example. Many older properties do not have a DPC.
Where appropriate, PTL will install a chemical DPC system to control the problem. The chemical DPC is injected into the walls at regular intervals. There will often be a small level of moisture held in the substrate due to salt contamination even when rising damp is controlled. Re-plastering will replace the salt contaminated plaster and protect the decorated surface from any residual moisture held in the wall.