Damp proofing is a protective process to ensure moisture cannot pass through the walls of a building to the interior.
Rising damp in buildings may be defined as the vertical flow of water up through a permeable wall structure, the water being derived from ground water. The water rises through the pores (capillaries) in the masonry. In other words the masonry acts like a wick.
By natural evaporation from the surface of walls, rising damp seldom occurs above a height of 1.2 metres unless forced higher by being sandwiched between two impervious layers of render, gloss paint or wall paper. Temporary measures, like cleaning the surface, replastering or just repainting can actually make the situation even worse.
The rising damp also carries with it hydroscopic salts (nitrates and chlorides) and as dampness evaporates from the wall surface the salts are deposited in the plasterwork, which build up into a concentration, that can absorb moisture from the air making the situation critical.
Rising damp can be more serious than just causing aesthetic damage, structural damage to the base of the wall can also occur which if left unchecked could lead to dire consequences.