What is salt damp
Nitrate, chloride, sulphate and ammonium salts are found in building structures.
Nitrate and chloride salts most commonly originate in the ground. Their presence in plasterwork is usually an indication of rising damp, lateral penetrating damp or flood damage. Nitrate and chloride salts are hygroscopic, causing them to retain moisture and absorb additional moisture at times of high humidity. Coastal properties may suffer from chloride salt contamination due to the salt water carried in the air.
Sulphate salt contamination of cement based plasters results in the cement content expanding up to 3 times its original mass and the plaster breaking down. Sulphate salts however are not typically hygroscopic.
Ammonium salts are a by-product of the burning of fossil fuels and are commonly found in chimney flues and chimney breasts. Nitrate and chloride salts are also found where ammonium salts are present. Ammonium salts are generally hygroscopic.
It is important when re-plastering a wall affected by salts that careful consideration is given to the type of plaster used. The water content of new plaster encourages salts to migrate from the underlying wall structure to the new plaster resulting in further problems. Chemicals are available to neutralize problematic salts before re-plastering work is undertaken.
Salt damp is closely associated with rising damp. When a new damp proof course is installed the lower wall areas are re-plastered with salt resistant plaster. Where damp proof course plaster has not been taken high enough a salt band may occur.
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Sat February 18, 2012, 10:05:17