brown stians in plaster

4 Feb 2008
Reaction score
United Kingdom
help please!!
we have had a new damp course cream injected into our property walls and the internal walls were stripped bear of plaster up to approx 12000mm because of previous damage to the plaster from damp.
our plasterer scratch coated and rendered then finished plaster the walls upto the 1200mm mark. he added a waterproof chemical into the render.
we are now 4 months later getting a gravy like colour coming through the paint above the line where the new plaster was this old damp coming through from the brick work ? can any one explain or help?
we have put approx four coats of paint onto the wall and it is still showing.
we are also getting marks on other walls some are brown spots approx 10mm diameter.
thank you.
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It could be coal tar that has been in the sand used to make mortar/render

Or the chemical waterproofer itself is not mixed thoroughly...this is less likely. Just noticed it`s not actually on the new render so this is not applicable. Maybe something transfering through the existing brick.


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