Contributed by Perry White, CSI, CCPR
When you think about painting drywall in commercial structures, everyone is a critic when it comes to how it looks. Anyone can see surface imperfections and usually people come back on the paint job and say what is wrong with it. In many cases that thought is incorrect!
Today’s drywall is usually recycled or imported and though there is nothing wrong with it, a 4’ by 8’ sheet can have different levels of porosity across the board. Drywall viewed under a microscope is very rough and imperfect. When installed, taped and mudded, you have different levels of porosity on those areas. If the installer hits the face paper when sanding the tape joints, little paper hairs will stick up and that is also visible to the eye.
What people are seeing is an optical illusion caused by light coming across the board which makes the final paint job look shaded or lacking in paint and sheen level. Since most commercial drywall is smooth without any texture, surface imperfections are highlighted. Porous drywall can suck the sheen out of the paint job and leave holidays, “flashing” or flat areas when a sheen like eggshell, satin or semi-gloss are used and will highlight these areas even more.
There seems to be a trend today for architects and specifiers to only specify a Level Four (4) finish leaving the final product to the paint contractor to make acceptable. A Level Five (5) finish includes a skim coat of drywall mud or texture. This is difficult to achieve since the paint contractor has to accept the drywall as is and the paint film is usually no more than 3 mils (0.003 inch) DFT (dry film thickness). For comparison, the human skin is only 7 mils DFT. Any rework to the drywall will also show where those patched areas are, especially if the patchwork was not primed prior to applying the final coat(s) of paint.
The key to creating a homogeneous looking surface is multi-faceted. Many primers used by drywall or painting contractors are low-cost, calcium carbonate or clay based primers with little or no acrylic resin to seal up the different levels of porosity in the face paper and tape joints. This is a critical component to creating a finished system due to the lack of a sealed substrate. These low-cost primers make the surface look prepared, but they remain porous. There are better, resin-rich primer/sealers that all paint manufacturers sell, but many contractors don’t want to pay the higher price.
If the first coat of paint has a sheen, it will disappear into the primer where there are higher levels of porosity. Those areas will look flatter and can be viewed at a low angle to the wall. That first coat in reality becomes the sealer. It now takes two coats of finish paint to get to that 3 mils DFT to achieve the sheen level necessary to touch up the wall if damage is done by other trades. The Painting and Decorating Contractors Association has standards to describe what a finished wall should look like.
The second key to getting the finished paint system to look acceptable is to back roll each coat of paint immediately as it is sprayed. This method is preferred and achieves three key things. First, it evens out the spray pattern across the board as it is not always done correctly to overlap each pass by 50% with your spray gun. Most spray tips wear out inside of 100 gallons so that the spray pattern is reduced from a cat’s eye pattern to one that looks like a water hose. Back rolling will even out a poor spray job to ensure that the paint is consistent across the whole wall.
Back rolling also forces the paint into the substrate to maximize the paint or primers ability to seal up the surface, making it easier to achieve the desired final paint millage. Back rolling will leave a slight stippled pattern on the smooth surface that will help hide any other surface imperfections. This will allow for the painted finish to be touched up easily with a roller with that same knap. Many painting contractors don’t back roll, but this leaves the finished surface hard to touch up since just spraying leaves a smooth profile and any applicator applying paint will show up either as brush marks or the stipple from a roller. It costs more to have that second person back rolling behind the person spraying, but the final result will eliminate most punch list issues due to poor sheen evenness or rework.
The open bid process could be improved to require that back rolling be part of the specification, but application methods are usually left to the contractor and are not part of the specification. If painting contractors understood that the finished product will stand up to more abuse during the final construction process and reduce touch up issues during punch out, maybe more would apply the paint this way. It certainly leaves the owner and their maintenance team with a more manageable substrate to work with and with the ability to touch up the surface in the future.
The Paint Quality Institute (www.paintquality.com) has a problem solving section that speaks to these issues on substrate porosity, surface imperfections, application and touch-up. Temperature variations of even 5°F can change how the paint film cures, creating issues when the paint was originally applied that can affect how the touch up looks.
Many people want to blame the paint or applicator for the finished product, but we can see that the answer has many moving parts.
Let's Fix Construction is an avenue to offer creative solutions, separate myths from facts and erase misconceptions about the architecture, engineering and construction (AEC) industry.
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