It is important to identify the correct cause in order to treat the problem and not spend cash unnecessarily
Rising Damp is the transfer of moisture from the soil to the foundations of a wall. The absorption continues into the bricks via Capillary Action. The Rising Damp carries natural ground salts such as nitrates, chlorides and sulphur, which can sometimes be seen on the surface of the plaster as white crystals.
What is capillary action ?
Bricks are generally full of tiny fissures, some are narrow and some are wide. The water gets into these fissures and the surface tension created allows the water to rise. The more narrow the fissure the higher the rise of dampness.
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How high will damp travel up a wall ?
There is a common misconception that Rising Damp only travels 1 metre high. In fact the height that damp can travel depends on many factors such as the density of the brick (as stated above, narrow fissures result in water rising higer) or whether the evaporation of the water is only possible from one side.
A good indication of how high Rising Damp has travelled is the white salt band that can some times be seen because the salts are carried with the water.
The ground salts carried up via the Rising Damp contaminate the wall plaster. As the damp evaporates, the salt migrates to the surface of the plaster and can sometimes leave a salt band.
These salts are sulphates, nitrates and chlorides. The nitrates and chlorides are hygroscopic, which means they have the ability to absorb moisture from the atmosphere, where it will condense to form water. The wall plaster will always appear damp, although the bricks under the plaster may be dry.
Sulphates are not hygroscopic but they can attack and break down cement. This is a real problem if sand and cement render has been applied.
The installation of a Chemical Damp Proof Course (DPC) into the base of the wall, supplemented with (a) a Vertical Damp Proof Course, and (b) replastering will cure the problem.
The chemical is installed either as a cream or liquid into the base of the wall. The walls of the fissures are lined with silicone to make them very slippery, reducing the surface tension of the water and stopping its ability to rise.