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August 31 - September 6, 2019

What is an acceptable level of moisture in concrete walls before painting with an acrylic system, and how is the moisture level measured?

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From Zenith Czora of Durotech Industries, Inc. on September 4, 2019:
Depending on the type of the water-based acrylic coating and its breathability, the setting and bond of these coatings are more forgiving to the presence of moisture than the solvent- based coatings,  but the presence of moisture will retard the film formation ( Water-based acrylic coatings dry by water evaporation.). The concrete wall is deemed dry enough to coat when the moisture content is not more than 5.5%. Using an electrical impedance moisture meter, moisture content is measured not only on the surface layer, but the measurements are made to a depth of several centimeters. It is not only the presence of moisture in the concrete wall that would be a concern, but also the salt component. which is inherently present in cement. The moisture within the concrete wall will dissolve the salt and the "salty" water migrates through concrete to the surface where water can evaporate, leaving the salts behind on the surface, forming efflorescence. The inherent alkalinity and the salt content of the concrete/cement can cause problems to coatings. It is most important to apply a highly-alkaline-resistant, water-based primer to inhibit the occurrence of efflorescence. A breathable wall coating is best recommended. A failure to 'breathe' can quickly cause a coating to blister and lose adhesion.

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Tagged categories: Asia Pacific; concrete; EMEA (Europe, Middle East and Africa); Good Technical Practice; Latin America; North America

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