WHAT IS RISING DAMP?

Most people associate rising damp with water, but moisture (not water) is the key to understanding rising damp. 

Here is why. The ground is always moist. Brickwork is naturally porous and absorbent. Moisture from the ground creeps up through the pores, or capillaries, in the masonry. Without a damp proof barrier to stop the moisture from rising in this way, the brick or other materials will continue to draw moisture form the ground until it eventually reaches its own level. That level depends on conditions such as humidity, temperature, evaporation, and the type of construction and insulating materials used. 

Masonry with fine pores, for example, will allow moisture to rise higher than a more coarse material. A humid environment slows evaporation, which also allows the moisture to rise higher. Where evaporation is severely inhibited (for instance, because of the use of sealants) moisture can sometimes rise more than two metres. Most often, rising damp will reach a level of about one metre.

SALT IS THE CULPRIT

Ground water contains soluble salts, such as chlorides, nitrates and sulphates. These salts in solution with the ground moisture rise up the wall and are left behind when the moisture evaporates. Over time, large quantities of these salts are deposited in the masonry and decorative surface of the building. Salts (not dampness) cause most of the damage.