Q: We have finished and painted a drywall job where there is often direct sunlight beaming on the walls through large windows. In many places, but not all, both the butt joints and the tapered joints can be seen. All walls have a Level 5 finish, using the joint compound applied with a trowel to the whole wall. All walls were primed and then sanded. In addition, a lot of walls had more than Level 5, as we went back in and made further visits once the walls were primed and lit with a lamp to try and make the finish near perfect before applying the finish paint. The top coats were not watered down but applied straight out of the bucket. We suspect that the premium eco-friendly paint might be a bit thin. We have some units where we were able to use different paints, and they are a lot better in terms of the banding.
A: As for the vertical butt joints, that condition is typical with drywall viewed under critical lighting conditions unless you use some type of device that pulls the ends of the board into the wall cavity before finishing (see this topic discussed more thoroughly in our July 2013 issue). You can apply wider swaths of compound at the joint to diminish the effect, but there will likely still be some shadowing. Perhaps the only way to avoid this is to use a veneer plaster system in which the whole surface is leveled out with almost a 1/8-inch of plaster by someone who’s been doing it for a long time.
As for the tapered joints, it sounds like you’ve answered your own question. If a different paint gives a better result in near-identical conditions, there’s not much else to discuss. A light sanding and dusting of the offending surfaces and a recoat with a paint product that has already demonstrated better performance—shot to the desired color—should do it. I would absolutely have the paint manufacturer’s factory representative look at both applications first.
That said, this situation is one that I saw many times during my tenure as a tech rep for a regional paint manufacturer years ago. While you would expect to detect the butt joints in critical lighting, generally the edge joints are not so easily seen if treated properly and then a Level 5 finish is applied prior to decorating. The first thought that comes to mind is that the paint is not hiding the joints as well as you would expect due to the color difference between the joints and the drywall. Even with a trowel-applied skim coat, the joints are likely to be a lighter color that the surrounding paper facing on the wallboard. Many primers designed to seal drywall and joint compound do not offer much in the way of hiding; they’ll obscure the surface but won’t totally hide the color change from paper to joint.
But there are several reasons that a finish coat of paint may reveal the finished joints. First, as described above, there’s not enough paint on the wall to hide the difference between the color of the bare drywall and the joint compound; second, the color of the finish paint is one that does not hide well (clean colors, particularly those containing yellow, can be infuriatingly transparent and are best applied over a good, solid coat of white); third, the joints have been finished and sanded in such a way as they have a different profile/porosity from the drywall, which is why a skim coat is often recommended in severe lighting conditions; fourth, the finish paint was applied directly over the drywall surface without a primer, which has resulted in a sheen developing over the joints different from that of the wallboard facing (also a reason to skim coat and then prime). Oddly, this final condition is more likely to occur when using a high-end flat than a cheap "maintenance” flat.
In this case, we know a skim coat and extra joint compound were necessary to bring the surface into the same plane, so the likelihood that it’s profile/porosity difference is all but eliminated—unless the additional joint compound was applied over a primed surface and then another coat of primer was applied over the whole surface. In that case, there are two coats of primer in certain areas and only one over the new work, and that could lead to a smoother surface where there is now a double thickness of the primer and a duller surface where there is only one coat of primer. But again, in this case, we know that different finish paints over otherwise identical substrates yielded different results.
There are a couple of things that might fix a problem like this: pole sand the surface with 150 grit to get a uniform profile on the wall and apply another coat of finish, and/or apply a coat of good (acrylic undercoater) primer, which can be tinted to the final color provided it’s not one of transparent ones, and then apply another coat or two of the finish. Ideally, do a test patch of either or both to see if it works before doing the whole surface. And it’s always best to have the tech rep from the paint company take a look before attempting a job like this.
Lee G. Jones is AWCI’s director of technical services. Send your questions to firstname.lastname@example.org, or call him directly at (703) 538.1611.