Hygroscopic Salts Flashcards
What are hygroscopic salts?
Salts from the fossil fuels burnt in a chimney can be deposited in the brickwork. This salt can attract moisture through osmosis. The moisture can appear as colourless staining on the chimney/ finishes around the chimney
Hygroscopic salts can also cause damp issues in other areas of buildings, for example rising damp
How did you determine the defect was hygroscopic salts?
The dampness was in the shape of the chimney on the newly plastered wall.
I asked the homeowner about any work which had been done to chimneys in the area. A chimney had been removed however no DPC or other barriers had been put on the brickwork before plastering.
The area wasn’t exhibiting any of the signs I would expect of damp coming in from externally e.g. damp from above etc.
What was the proposed remedial solution for the hygroscopic salts?
Prevent the water from reaching the area of the hygroscopic salts
Remove any finishes, for example plaster
Replaster with a plaster containing a salt inhibitor and water proofing
Air gap membrane systems can also be used to deal with the issue (e.g. similar to used in damp proofing/ tanking systems)
Did the hygroscopic salts return?
What methods could be used to determine conclusively the salt content of the wall?
