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Paints and Coatings: Tackling Tricky Applications
OTHER PARTS OF THIS ARTICLEPt. 1: Making Painting Projects WorkPt. 2: Understanding New-Generation Paints and CoatingsPt. 3: Paints and Coatings: Successful SpecificationPt. 4: This Page
One especially challenging paint and coating application involves applying epoxy coatings to masonry surfaces. Among the most common problems and errors involved in such projects are these.
Preparation. Poor preparation tops the list and shows itself by peeling and delamination of the coating. Workers can avoid this problem by thoroughly cleaning, drying and roughing the surface by acid etching or grinding. Roughing the surface is essential to open the concrete pores for better adhesion. This step is just as important with new concrete as with old.
Moisture. Workers can avoid moisture trapped after etching by making sure the concrete is dry before applying the coating. Do a moisture test by taping a square of aluminum foil on the surface. If water condensate is visible under it after several hours, moisture is wicking up through the slab. Workers must dry the substrate and seal it properly before applying the epoxy.
Thickness. Workers can avoid stretching epoxy too thin and allowing enough material for the job by figuring about 15 percent shrinkage. They also need to avoid scraping the bottom and sides of the coating tray because this material might not be thoroughly mixed, causing early failure.
Mixing. Workers can avoid faulty mixing by slowly mixing the coating with an electric paddle to prevent trapping air. Also, paying close attention to the part A and part B ratio can ensure more reliable results.
Weather. Workers must not apply the coating when temperature and humidity levels are outside those recommended by the manufacturer. Too much heat reduces pot life, and moisture in the mix causes early separation.
— Thomas A. Westerkamp