When assessing isolated or sporadic dampness, an experienced surveyor can identify the cause and request further specialist investigation if required. In normal circumstances, once the original source of the dampness has been repaired, a short drying out period will be sufficient to resolve the damp but when salts are present reoccurring dampness remains, causing damage to decoration and adjacent joinery.
Hygroscopic salts are minerals found in masonry which rapidly absorb moisture from the air. This results in repeat wetting to the affected areas. In attempt to reduce heat loss, homeowners commonly block ventilation pathways and combined with the increasing use of hot water appliances, room humidity levels in the average home are high. High humidity is particularly problematic when hygroscopic salts are present, making salt-dampness a persistent defect.
Salts are drawn to the surface of walls during the drying process and can saturate plasterwork. Affected areas will normally show salts on the surface of the plaster which is bitter to the taste (although we do not advise tasting salts!). Affected areas may not always show salt residue on the surface, but they will feel greasy to touch. The problem can be particularly obvious in chimney breasts when the products of combustion combine with salts lining the flue causing continuous dampness.
Naturally increasing ventilation will go part of the way to remedying the problem of salt-dampness however there is invariably the need for replastering to and around affected areas. Gypsum based plaster should be avoided as salts will continue to be drawn into the material and the problem will not be rectified. The use of a suitable, vertical damp proof membrane or cement based waterproof coating is considered suitable as remedial action. Alternatively the damp wall can be completely isolated from the internal wall surface making it impossible for salts to migrate through capillary action.
It should be noted that the presence of salts in masonry complicates damp detection: Chlorides and nitrates (salts) conduct electricity which can fool a damp test with an electrical capacitance meter, which is calibrated to test the relative moisture content of timber. This may lead to false readings being displayed and the tested area appearing damper than it actually is. Having a surveyor inspect the property will ensure that salt dampness is identified and the appropriate remedial action is carried out.