Certain salts, nitrates and chlorides are left behind when soil water evaporates (rising damp) on the surface of walls. A meaningful analysis can be carried out provided plaster on a wall has not been disturbed for several years. Rising damp can be caused by a missing damp proof course but it may be due to other defects including bridging, plumbing leaks, rainwater penetration, condensation, and other factors.
Salt can build up to high concentrations particularly in plaster which makes it damp. You can also detect the salt and moisture with an electronic moisture meter. If chlorides and nitrates are present in the stonework or plaster it may indicate rising damp.
Blistering, corrosion, decay, delamination, efflorescence and freeze/thaw damage are just a few of the common defects associated with moisture in a building. Delamination applies to laminated materials, composite materials and reinforced concrete structures. It means repeated impact can cause layers to separate, forming a mica-like structure of separate layers, which reduces the mechanical toughness of the material. Efflorescence is a crystalline deposit of salts often seen on the surface of concrete, brick, stucco or natural stone surfaces. It occurs when water leaves behind salt deposits and is present on or in the masonry surface.
Salt Tests test the presence of nitrates and chlorides
All you need to do a salt test is the correct amount of two chemicals packed in sachets for each test, a bottle of distilled water, and two measuring beakers. The test is very simple and takes just a few minutes. A colour change will indicate whether or not certain nitrates and chlorides are present.
You can test a sample of the wall covering or plaster by removing it from the wall and mixing it with distilled water to form a solution. You add chemicals in the form of pill, one nitrate 1 tablet to a 10cc vial of distilled water. This turns the solution yellow. Then you add a nitrate 2 tablet, shake for 30 seconds and leave to stand for 5 minutes. If nitrates are present, the solution will change colour, brown for traces of nitrate, red for significant amounts of nitrate. If the solution remains yellow, nitrates are not present.
To test for chlorides you add one chloride tablet to the 50cc solution and shake the container until the tablet dissolves. If the solution is brown, there are no chlorides present but if the solution turns yellow, it means the solution contains chlorides.
The diagnosis of the origin of salts should not be made on the presence of salt alone, but considering other information available such as the moisture distribution within the building. A high reading of nitrates may signify that evaporation of soil water has continued for a long time. Soil salts are hygroscopic which means they absorb water directly from the air.
Be careful to distinguish nitrates in tap water from rising damp
However, when running the test, you must be careful because tap water often has nitrates in it too. For this reason, it is advisable to test your tap water first to establish a baseline nitrate level before testing your walls for rising damp. If the level in your plaster or wall covering is higher than the level in your tap water, this suggests you have rising damp caused by soil water on the surface of your walls.
You also need to take care when choosing your nitrate test kit. The most common kit is the Protimeter kit but the solution it provides simply reacts to nitrates present. Some of the other kits provide a colour chart such as a test kit manufactured by Salifert so you can compare the colour of the solution mixed with tap water and compare this with the solution mixed with wall coverings.
Salt tests are just a small part of the service that CPL t/a Rainbow International can offer to customers. DOFF, TORC and other media blasting techniques such as ice blasting, soda blasting, water blasting and pressure washing can all restore your building to a pristine condition.