Rising Damp is not the most common form of dampness found in buildings but is possibly the most discussed. In modern days, Condensation is the most common form of dampness but positive identification and appropriate remedial action for both is essential. Rising damp in buildings may be defined as the vertical flow of water up through permeable wall structure, the water being derived from the ground. The water rises through the pores (capillaries) in the masonry. In other words, the masonry acts like a wick.

Water rises up through the mortar beds and through the bricks. The mortar forms the only continuous pathway for water to rise up the wall. Even if a house is built from impervious bricks then water can still rise through the mortar beds, but if an impervious mortar is used then no water will rise, even if the bricks are very porous. It follows that the mortar beds are an important element in the chemical treatment for rising damp.

Ground water contains small amounts of soluble salts including chlorides, nitrates and sulphates. These pass with the water in solution up the wall and are left behind when the water evaporates during drying. Over a period of time these salts accumulate and leave a ‘salt band’ towards the maximum height of the rising damp. Both chlorides and sulphates absorb moisture from the environment. In general the greater amount of salts the greater the absorption of moisture especially under humid conditions. Therefore even if the rising dampness has been controlled by the insertion of a damp proof course these salts alone can cause the wall and any contaminated decorations to remain damp.