Salt contaminated plaster patching around an electrical socket highlights the importance of using salt resistant plaster on old brickwork to avoid damp problems.
One of our surveyors was recently asked to explain the cause of dampness affecting plaster around an electrical socket in a Victorian terrace house. The wall was re-plastered several months earlier but more recently the electrical socket and back box had been replaced. The electrician had plaster patched when making good.
The electrician had unfortunately used gypsum plaster for the patching work rather than cement or lime based plaster. Gypsum plaster has a low resistance to the salt contaminants often found in brickwork in older properties and a high moisture retention. Hygroscopic salts had consequently contaminated the plaster and caused the dampness. The plaster around the patch was unaffected as it was a cement based and salt resistant.
Dampness affecting plaster around sockets, light switches and where electrical chases have been plaster patched is all too common due to a lack of awareness of the potential for damp problems and therefore the use of inappropriate plasters.
The solution in this case was to remove the salt resistant plaster and re-plaster with RendX salt resistant plaster.