PaintPRO , Vol. 6, No. 6
November/December 2004
PaintPRO Vol 6 No 6

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Related Readings:
Primers & Topcoats
Coating Drywall
Drywall Priming
Priming Interior Woodwork
Effective Surface Preparation
Drywall Repair & Painting
Other articles in this issue:
Coating Drywall
Masonry Stains
Primers & Topcoats
Education Focus: Faux Masters Studio
Estimating, Etc.
Contractor Profile: John W. Dee
Manufacturer Profile: UGL
Product News
Painting Tips
 
PaintPRO Archives
pg 1 of 2
dry wall 1

 

 

Drywall, Primers
and Coatings

Drywall, Primers and Coatings. Experts offer their thoughts on using primers, skim-coats or surfacers to get the best possible finish.
by John Strieder

Drywall is just dried gypsum plaster in a sandwich of thick paper. But it gets a lot of love.

Code enforcers like drywall because of gypsum’s ability to retain water. It steams when exposed to flame, so it’s a solid fire retardant.

Builders like it because hanging gypsum board takes only a fraction of the time needed to plaster a wall. Just nail it up, set joint compound and tape in the valley created by the slabs’ tapered edges, and slather in more joint compound to fill the valley. Presto! A finished wall. Well ... almost.

dry wall 2Even after sanding or sponging, a gypsum-board wall is not ready for paint. The soft crown of joint compound looks nothing like paper, and doesn’t accept paint the same way either. How does a contractor create a smooth, attractive surface from such muddy beginnings?

Primer is primary
The biggest problem is porosity. Drywall paper and joint compound absorb moisture at different rates, and the paper accepts paint unevenly from one square foot to the next. So the first coat of paint will likely result in a very patchy finish, with shiners and dead spots. The glossier the paint, the bigger the problem.

A coat of semigloss on drywall can turn satin or flat, says Steve Revnew, architectural coatings marketing director at Sherwin-Williams Inc. That’s why, like most experts, Revnew says a preliminary coat of primer is essential when painting drywall with anything other than flat paint. “If you do not use primer, you’re not going to get full gloss and sheen development,” he says.

Levels of Drywall Finish
Thanks to four trade groups, including the Painting and Decorating Contractors of America and the Gypsum Association, there is a standard chart of five “levels’ which, when used by architects, contractors and customers, describe exactly to what specification a gypsum-board wall is expected to be finished.

Level one, the roughest on the chart, is for temporary construction. It requires simply “tape set in joint compound” on joints and interior angles. Tool marks and ridges are “acceptable,” and the surface need only be “free of excess joint compound.”

Contractors working toward smooth painted surfaces or the use of light- or medium-weight wall coverings will be more interested in level four or level five.

Level four, recommended where flat paints, light textures or wall coverings will be applied, calls for joints to be covered with two extra coats of joint compound after taping. Interior angles get one extra coat, while accessories and fasteners get three. The surface must be “smooth and free of tool marks and ridges.”

Level five, for gloss, semi-gloss, enamel or flat-textured paints and severe lighting, mandates a uniform surface with minimal joint and fastener show-through. The standards require everything in level four with one addition: “A thin skim coat of joint compound, or a material manufactured especially for this purpose, shall be applied to the entire surface.”

A coat of drywall primer prior to the application of final finishes is recommended in levels three, four and five.

Jeff Broker, who markets interior finishing systems for U.S. Gypsum Co., agrees. “To ensure a better finish, it’s always recommended to prime it,” he says. “A good heavy-bodied primer will equalize those surfaces.”

It’s true, multiple coats of high-end paints will also smother the flashing problem. “Two to three coats of eggshell may be enough for holdout,” says Ron Boyajian, product marketing manager for California Paints. “More often than not another finish coat gets the job done.”

But a primer will promote adhesion, a good reason to use one even with a flat, Revnew says. “Could you get away with not using it? Yes. But standard flats will not always have great adhesion to drywall.”

Primers create a protective barrier against stains, odors, and in some cases moisture vapor. They even protect a finish from the drywall itself. The paper in drywall is often recycled paper, saturated with waxes and inks that bleed onto the finish coat, Boyajian says. “It’ll look like a little shadow.”

As for application, primers spray just like paint, with only the same difficulties posed by spraying paint. “You’re subject to all the pitfalls in primer that you would find in a finish coat,” he says.

Skim-coats
Gypsum board manufacturers promote another method of sealing drywall: skim-coating. A thin layer of joint compound, spread with a trowel across the entire surface of the drywall, solves the porosity problem. It plasters a smooth textured finish over paper and joint and masks other imperfections in the drywall.

When it comes to drywall, smoothness is a big deal. So big, in fact, that industry trade groups have devised a chart that describes five grades of finish and how each is achieved. Thanks to the chart, contractors, architects and building owners know they are speaking the same language when they spec drywall. (See sidebar.)

A skim-coat of joint compound or specially made skim-coat material is mandated at level 5, the top level of drywall finishes. But skim-coating is costly, says Lee Jones, spokesman for the Gypsum Association, a manufacturers’ trade group. “If it’s not necessary, it’s truly expensive, an unnecessary expense.”

So its no surprise that manufacturers are busily developing spray-on, high-build products that offer the benefits of both primer and skim-coat in one surfacer.

 
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