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Question posted - November 20 to November 24, 2017:

Do I need to pay attention to the permeability of the coating when specifying coatings for the exteriors of CMU walls?

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Selected Answers

From Zenith Czora of Zen Consultancy on November 20, 2017:
Breathable paints ( high water-vapor permeability) enable humidity within the CMU walls to escape quickly unhindered into the environment, preventing moisture build-up between the coating and the substrate. Breathability allows a coating system to perform well, free of defects, because paints with high vapor permeability allow moisture to pass through, rather than being trapped behind the coating. If moisture becomes trapped, it will build up behind the coating, eventually leading to blistering, flaking and delamination of the paint layer (adhesion failure). Moisture being trapped will saturate in the substrate, which may lead to a friable substrate and will be costly to repair.The higher the number of the moisture vapor transmission rate, the more moisture vapor that the coating material will allow to pass through and the better the drying the coating material allows. This is only applicable for breathable coating. A coating should be breathable enough to allow moisture to escape through as temperature and humidity change, but does not permit bulk liquid water to penetrate the wall and withstands penetration by wind-driven rain.

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Tagged categories: Concrete masonry units (CMU)

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