I noticed in your Q&A archive that someone else has written in about the black shadow problem on the exterior walls, under the Dust section. You mention to use specific paint to cover/clean it up. What is the underlying problem and how should it be solved so these shadows do not reoccur?
Answer:
The problem is a lack of vapour barrier over the insulation behind the plaster board in the area so condensation forms and stays longer than it does elsewhere. If there is less than adequate insulation, and more importantly, continuous vapour barrier on an exterior wall or ceiling, the ceiling shows dark shadows. These are the result of solid particles in the atmosphere having stuck to that part of the plastered surface that remained moist the longest after condensation soaked it from behind. The staining always follows strapping or other structural components behind the plasterboard because wood holds moisture better than insulation. This process normally takes years to show up as shadows. Rectification entails painting the stains with a stain deadener, prime painting the area and then giving it a finishing coat.
Courtesy of Ren Molnar, Construction Consultant at HomeFocus.com. I can also be reached at (613) 748-3003 and Home Focus – The Radio Show is broadcast live 8 to 10 A.M. (Ottawa, Ont. time) on Saturdays on www.cfra.com. In the interests of retaining credibility and in fairness to all, I cannot recommend prices, people nor companies for various projects.
Remember, even if you don’t do your own work around the house have to hire someone, you put yourself at a great advantage when you can intelligently discuss a project with the various trades people.
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