Natural soluble mineral salts are commonly found in soil. When rising damp occurs, nitrates, chlorides and efflorescent salts migrate through the masonry in solution and accumulate on the wall surface as a white powder.
These salts are hygroscopic and attract moisture from the atmosphere, particularly during periods of high humidity, and give the effect of persistent dampness and associated damp smells.
Salt contaminated solid plaster will continue to attract atmospheric moisture even after the rising damp has been stopped.
To prevent this secondary damp problem the affected area of solid plaster must be removed. The removal and replacement of plaster forms part of the F.G. James system.