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November 20 - 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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From Zenith Czora of Parex Davco 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: Building Envelope; Concrete masonry units (CMU); North America

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