Exterior Paint, Enamel Paint, Enameling Smooth Wall Surfaces
Achieving a uniform enamel finish over a smooth or lightly textured wall surface is no easy task. But for a seasoned paint professional able to recognize and solve potential problems before beginning the job, it's all in a day's work.
Achieving a uniform enamel finish over a smooth or lightly textured wall surface is no easy task. But for a seasoned paint professional able to recognize and solve potential problems before beginning the job, it’s all in a day’s work.
Several factors make enameling smooth or lightly textured gypsum wall surfaces one of the most difficult applications within the painting profession. The essential problem is the porosity of the drywall, or, more precisely, the difference in porosity between the face paper and the drywall mud, which when painted dry to different sheens.
For this reason, it is important to understand how gypsum board finishes are specified, so you can be sure that the surface to be painted is prepared for an enamel or gloss paint. The sidebar, Levels of Gypsum Board Finish on page XX, shows the five standards of drywall preparation.
“From a paint contractor’s perspective, it’s important to understand the five levels for gypsum board finish. You need to take some time to understand the standards of the other professions so you can intelligently discuss them,” says Mark Robson, president of Ram-Mar Painting Inc.
“When a paint specification calls for a smooth surface, it’s important that the level of gypsum board finish correlates,” adds Steve Shephard, president of Shephard and Son Incorporated. “If a high-gloss paint is requested, I usually try to put disclaimers into the specifications—the higher the gloss, the more chance that imperfections on the drywall will show through,” he says. And if the job calls for a high-level paint finish, then the specifications should call for a level five gypsum board finish. The fifth level finish is the most effective method to provide a uniform surface and minimize the possibility of joint photographing and of fasteners showing through the final decoration. (See page 29 for descriptions of the five levels of gypsum board finish.)
However, even when the gypsum board finish does correlate to the job at hand, “It’s important to do a preliminary check” on the finish, says Robson. Spotting potential problems before beginning a job can save both time and money, not to mention preventing an unhappy client. Both Robson and Shephard suggest a good general inspection of the wall surface prior to beginning a job. The tools required for this inspection are a good high-powered flashlight and a level. Robson uses them to check for imperfections that will show with a high gloss finish or in critical light areas. “Look for sanding dust, over- and underfilled joints, uneven wall surfaces, over-sanding and bad framing. A good high-powered light will help to highlight several surface problems,” says Robson.
Both Robson and Shephard also advise paint contractors to begin a job by painting a mock-up wall for the client. This small test wall provides clients with an example of how the finished product will look under the specified conditions. “It’s important to show the client what the wall would look like using the current specifications. This will highlight any problem areas and provide ample opportunity for the contractor to repair the wallboard or to re-specify the job before beginning to paint,” says Shephard. “The warning signs to look for in job specifications are variable.”
Once the gypsum finish has been inspected and a mock-up wall has been completed, the next step is application. However, there remains one important thing to look out for in applying enamel paints to drywall. When drywall sheets are all from the same manufacturer and the same production lot, the coating’s finish will probably be relatively uniform. However, it’s not unusual for drywall from different manufacturers, or from different production-run lots from the same manufacturer, to be installed on a job, especially if it’s a large job. “The more brands and lots used, the greater the chances for different sheens,” says Robson.
This means that the finish across the entire painted surface—a hallway wall, for example—may vary from panel to panel. These problems are compounded when strong, direct lighting is added to the equation. Not only are the differences in sheen more readily noticed, but small imperfections such as uneven joints, nicks and scratches are highlighted. The coat may also be flatter than expected.
“It’s important to take steps that will provide for uniform porosity over the entire surface, and that means a good primer,” says Robson. Without a good primer, the face paper sucks in the paint, which stands up at the joints, cau
sing a shadow because of the different textures. “Priming will equalize the porosity between the wall board and the joint compound,” he says.
There are several good primers that will level the topcoat, providing excellent holdout on multiple substrates of different porosity, while they maximize gloss. William Zinsser Co. Ltd’s B-I-N® Primer, Sherwin Williams’ Problock Interior Alkyd Primer/Sealer, and Kelly Moore Paints #971 Acrylic Acry-Prime Interior Latex Primer-Sealer are all good all-purpose primers which seal surfaces and provide a smooth base for finishes.
The application method also depends on client wishes. “If a client wants a perfectly smooth wall, a painter will have to skim coat over the surface, then sand it. The coats of application from that point will have to be sprayed. “There is no panacea for application,” says Robson.
Tip sizes for this application range from 11 to 17, and factors such as the ambient temperature should be taken into consideration. “The manufacturers recommendation for application should always be followed,” says Shephard.
Potential problems while using spray applications include over and under-atomizing. Over-atomizing results in a non-uniform cell thickness across the face of the surface, while under-atomizing will pile up paint on the wall. Under-atomizing, as well as a worn spray tip, tends to result in center shooting, leaving two heavy sidelines, and results in a checkerboard pattern.
On the other hand, if the client wants a lightly textured finish, that requires several coats of paint and a high enough fill-primer to begin the light texture process,” says Shephard. “Application comes down to a painter’s capability. A good roller man can put a surface on as uniformly as a good airless spray applicator,” he says.
High-build or fill primers are used to fill and eliminate minor surface defects such as paper fuzz, scuffs, nicks, pinholes and sanding grooves. “These primers are generally designed to equalize porosity of new construction wallboard paper and drywall compound. High-build primers allow for a consistent topcoat with no telegraphing tape joints or flashing enamels over mud seams,” says Andrew Kinnen, Product Manager, Architectural Coatings, for The Sherwin-Williams Company.
US Gypsum’s Sheetrockâ First Coat is one example of a high-build primer. “This latex basecoat is formulated to equalize differences between porosity and texture variations of gypsum board face paper and the finish joint compound to minimize problems,” says Van Perrine, of US Gypsum. The product is designed to go on with a brush or spray equipment and dries to a white finish in 30 minutes.
There is no quick or easy method to enamel a smooth or lightly textured gypsum surface. It takes advance planning and clear lines of communication with the general contractor regarding specification, as well as a good inspection, the right primer, and careful application. But with all these elements in place, the painting contractor will be able to guarantee smooth results.