When rising damp occurs and it makes its way onto internal wall plaster, it will deposit salts which are carried upwards from the ground with the damp. As damp continues to rise into a wall, it carries more and more salt with it and, as the damp evaporates, it deposits the salt, causing a gradual build up. When these salts are deposited on surfaces, primarily walls, this presents a further problem which has to be addressed in addition to the Rising Damp. Salts such as these are hygroscopic meaning that they will attract and hold any moisture from the internal air of a property which they come into contact with. The effect is that, even though the cause of the Rising Damp may have been cured, the wall on which the salts sit may still appear damp. In cases where salts are present on internal wall plaster, the most suitable remedy is to remove and dispose of the plaster, replacing it with a suitable decorative plaster. Rising damp remedial treatment(s) will always consider salt deposits.
When dampness has been rising in a wall for some time, the soluble salts contained in the ground become concentrated where the water evaporates, i.e. within the plaster and within the wall itself near the apex of rise. These deposits of salts can absorb water directly from the air to such an extent that the wall can become visibly wet. This dampness effect is entirely separate from that caused by capillary rise of water and is usually referred to as hygroscopic dampness.