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Best Practices:
The Pain in Painting Drywall

Tuesday, February 4, 2014

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Question: Can an ASTM Level 5 Drywall Finish produce a satisfactory painted finish in critical lighting areas and/or when using higher sheen paints?

Answer: It depends—on a variety of factors, including whether you ask a painter or a drywall finisher.

Here’s a history lesson. Not so long ago, walls finished with an ASTM Level 4 Drywall Finish could be finished with one coat of latex sealer followed by a very different intermediate than we commonly use today: namely, an enamel (alkyd) undercoat such as that approved under MPI #46.

Painted Drywall
Photos unless indicated: MPI

Today's coatings have changed the game of drywall finishing.

This enamel undercoat was thick enough to mask fine surface irregularities and fill the paper texture. It was also inexpensive and sandable, versus the latex intermediates we use today that don’t buff down like an alkyd can.

That enamel undercoat could then be topcoated with an eggshell or semigloss alkyd, especially on walls subject to abrasion, marking or wet areas (bathrooms, showers, janitor closets). And there was no discussion of texture imperfections telegraphing through the surface.

Flash forward to today: Alkyd undercoat enamels are, in our experience, virtually never specified for new construction, and a sandable, inexpensive, VOC-compliant replacement does not appear to exist.

Meanwhile, regulations have moved the industry to virtually eliminate alkyds for interior walls, replacing them with multiple coats of latex at a higher cost and lower volume solids—which means less material is deposited to smooth out the surface.

What Level 5 Does...

So now, we specify a Level 5 Drywall Finish to guarantee an acceptable surface in areas of critical lighting or where a glossier finish is required.

And although Level 5 consistently provides better results than Level 4, it’s no guarantee of a perfect finish.

MPI Painted Drywall

Two drywall surfaces are primed with latex sealer. Paper texture is on the left; skimcoat is at right.

Here’s the defining clause in a Level 5 Drywall Finish as described in ASTM C840’s Standard Specification for Application and Finishing of Gypsum Board:

“A thin skim coat of joint compound shall be trowel-applied to the entire surface. Excess compound is immediately sheared off, leaving a film of skim coating compound completely covering the paper. As an alternate to a skim coat, a material manufactured especially for this purpose shall be applied.”

...And Doesn't Do

So, yes, a properly executed Level 5 finish will eradicate the drywall paper texture. But there’s a popular misconception that it can also repair "proud" or "poor" seams, humps, bumps, or other defects.

It cannot. Level 5 can’t level the surface of the wall or eliminate many of the defects that plainly show in critical lighting areas, or where higher-gloss finishes are used.

In fact, the often-cited Gypsum Association’s GA-214-10E Recommended Levels of Gypsum Board Finish says that the Level 5 finish "is highly recommended where paint is specified or where severe lighting conditions occur” and that it’s the most effective method to minimize visible defects."

But the guide also warns that “a skim coat will not approximate a plastered surface. Once the skim coat dries, the gypsum board paper may show through, and the treated joints, filled voids, and spotted fastener heads will likely be visible.”

GA-214-10e
Gypsum Association

So, essentially, the Level 5 drywall finisher is telling the painter “the paper texture may be eliminated, but other abnormalities or variations [which we in the painting industry would call ‘defects’] may still be present."

Issues with Skim Coating

The overall quality of the skim coat plays a substantial role.

First, no specific mil thickness is specified in the standard. GA-214-10e points out that “a skim coat is essentially a ‘film’ of joint compound and is not a readily measurable thickness. There is no specific mil thickness that constitutes a proper skim coat.”

The quality may also depend on how the skim coat was applied.

Even though the ASTM standard says “trowel applied,” GA-21-4-10e cautions that “a skim coat is described as trowel-applied with the intent that the consistency (viscosity) of the joint compound be such that it can be applied by a trowel. Other tools may be used for application so long as the trowel consistency is achieved.”

Application Options

And in fact, with the joint compound skim coat materials currently on the market, there are three ways to apply them:

Skimcoating
www.wisegeek.org

The quality of the skim coat is critical and will depend on several factors.

  • Troweled on. This is the slowest and most labor-intensive method, but it effectively accomplishes what a Level 5 should do. The trowel allows a skilled applicator to create a level surface by applying an appropriate amount of material to the paper areas only, since adding more material on top of the seams or repaired areas is likely to create humps.
  • Roller application. Drywall surfacing compounds are also available for roller application. However, most drywall finishers do not have the roller skills and experience that painters typically possess, so all the flaws common to roller application may prevail, including skipping, roller tracking, and an uneven surface. Also, application with rollers tends to cover the seams as well as the paper, which contributes to a more uneven appearance.
  • Spray application. Some drywall surfacing compounds are now available for airless spray application. This can be a very efficient—a big airless sprayer can cover a large area fairly quickly—however, there are substantial drawbacks. Adhesion may be compromised; it’s not unusual for these compounds to readily come off when you try to sand them. Air entrapment can also be a problem, as can heavy buildup in some places and not enough in others, “fingering,” and other flaws typical of unskilled airless spray work.

When using roller- and spray-applied surfacing compounds, we also see issues with sanding. The material is very dry and powdery; after sanding, the paper texture often shows through, essentially eliminating the value of applying the skim coat in the first place.

With these issues in mind, thankfully, a lot of drywall finishers won’t accept roller or spray application for skim-coating drywall surfaces.

Level 5 v. Level 4

So what’s the solution?

MPI Drywall Painting

At left: Drywall Level 5 finish. At right: Level 4.

If we can’t have our old sandable undercoat enamel back with an acceptable VOC (and at a comparable price), and considering the surface irregularities that may still be present with Level 5 finishing, the inspector has found that for critical lighting areas and/or where a higher-sheen finish is required, requiring a Level 5 Drywall Finish may not be the most cost-effective solution after all.

And in our experience, it’s rarely specified anyway.

Instead, comparable results may be achieved over a Level 4 drywall finish by finishing the surface with drywall primer plus three coats of latex, instead of the customary two.

Adding the third coat of finish puts another 1.5–2 mils DFT of paint on the surface and can make the difference between unacceptable and acceptable.

You’ll see this yourself in repainting operations: A surface that was initially painted with a primer and two coats (and looked ok, but not great) will often look a whole lot better after its first repaint, when two additional coats are applied.

Editor's Note: This article was written by PQA Inspector Dave Lick and is reprinted with permission from the MPI (Master Painters Institute) newsletter. MPI content describes best practices for commercial, institutional, and light industrial painting.

   

Tagged categories: Architectural coatings; ASTM; Drywall; Interior coatings; Latex; Master Painters Institute (MPI); Paint application; Paint defects

Comment from john schultz, (2/4/2014, 9:22 AM)

It doesn't have to be just high sheen paints that create trouble on level 5 surfaces, especially on ceilings. Fast drying latex finishes can create a micro texture that shows roller stripes with angular light. It isn't noticeable until the sun comes shining through and then BAM. This effect can persist even after another coat. Enamel underocoat won't fix that I fear. Just a little texture on the ceiling would have been enough to break up the effect and make the surface look uniform.


Comment from Roderick Marsh, (2/4/2014, 12:32 PM)

Smooth wall level 5 spray applied PVA finish or roll out a coat of Inslx prime lock alkyd undercoat works for me.


Comment from Bill Connor, Jr., (2/4/2014, 2:31 PM)

Sheetrock First Coat properly applied and lightly sanded will eliminate the raised nap on new drywall but cannot correct defects in the tape job. Colorado drywall contractors use shims on non butt joint studs to allow butt joints act like recessed factory edges. I have not seen those shims in use in California.


Comment from Perry Eckert, (2/5/2014, 1:52 AM)

One of the main problems painting dry wall joints is that sanding dust is not removed before applying the sealer or primer. This results in a different surface texture which will affect the sheen level. We recommend wet dusting to ensure surface dust is adequately removed before painting commences.


Comment from Steve Seidman, (2/5/2014, 8:48 AM)

Dust can also cause subsequent wallpaper failure.


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