Hygroscopic Salts or Salt Dampness
Firstly what is hygroscopic plaster? One of the main causes of salt dampness is the ‘roof garden’. Weed within a chimneystack is a guaranteed bet that due to the long term water ingress the internal wall will be affected by salt dampness, and the chimney structure will require Rebuilding, more often than not a general builder, will simply scrape out the weed, and repoint. A few months later, the weed will be back and the internal wall will look like the examples below.
Salt dampness ‘The movement of hygroscopic organic salts into the plaster surface’ this results in staining, and persistent dampness of the applied plaster, due to these salts constantly absorbing moisture from the atmosphere. If not corrected the plaster will turn, deliquescent state which means they are dissolved within the moisture they have absorbed from the atmosphere, this becomes more prevalent where there is an increased moisture source as in this case by high relativity levels (Condensation).
The hygroscopic salts can migrate through capillary action into other areas some distance from the source of the dampness. It is of the up most importance that the correct remedial works are undertaken, to install the correct remedial systems. In the image above the contractor simply replastered the chimneybreast and installed standard plasterboard to the ceiling, six month earlier. Dry lining The installed dry lining in the image to the left, by an unqualified contractor who undertook a property refurbishment, this works were only completed a week, before and the salts are striking through the installed plasterboards, note he hasn’t even had time to remove his tools and post his bill.
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