American Painting Contractor Magazine

APCMay16

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such as the difference in coverage between a repaint and bare drywall. For that rea- son, many manufacturers provide a rec- ommended thickness to achieve 250 sf/gal and a thinner spec for 400 sf/gal. HOW THICK DO YOU APPLY? Think about paint in terms of "millage" or mil thickness. This term refers to the thickness in the coating, measured in mil- limeters. When you check a TDS, you'll find that many waterborne or latex products are recommended to be spread at around 4 mil wet thickness of product. As the paint off-gases and ingredients evaporate dur- ing the drying process, the product will produce a dry thickness that's significant- ly less than the wet thickness. In some cases, a paint will have a recommendation of 4 mil wet, resulting in a 1.5 or 2 mil dry thickness. That is a reduction of 50 percent or more as the product transitions from liquid to solid on a surface. Obviously, when the paint dries, it's the solids in the can that are left on the wall. Some of the more popular interior products, such as Behr Premium Plus Ultra, Benjamin Moore Regal Select and Sherwin-Williams Cashmere, fall in this application range. If you review their TDS, you'll notice they "dry to touch" within as little as an hour, and can be recoated in the two-to-four-hour range. Of course, these recommendations depend on temperature, humidity and thickness, all uncontrollable variables, making painter judgment and awareness (education) very important. Conditions can vary from day to day, so painters need to be observant and make adjustments every day. We all would love to be paint- ing machines working exactly the same way every day, but the human factor is an important part of the craft. PER COAT? TDSs are a helpful resource, but painters can misinterpret them. It's important to understand that manufac- turer TDSs calling for a particular thick- ness in the coating are referring to the total of all the coats required to do the job, not just one coat. In other words, the manufacturers are not saying the products are recommended to be applied at 4 mil wet thickness; if you can do that (for example, on a horizontal surface), great! But whether it takes you one, two or four coats to do your project, the total thickness of all coats required when using a product should add up to the recommended dry mil thickness. Many painters probably don't measure their coating thicknesses at all. They may go by coverage, color intensity or sheen; however, the manufacturer recommenda- tions are a good guideline to use to check yourself. It's best to do it before you push a product the wrong way and have a prob- lem. You may be using too much paint, or you may not be using enough. AMERICAN PAINTING CONTRACTOR • May 2016 13 From the Field

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