The Pain in Painting Drywall: The ASTM Level 5 Finish
Based on the experience of Paint Quality Assurance inspector Dave Lick
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. It depends on a variety of factors — including whether or not you ask a painter or a drywall finisher.
Here’s a history lesson: not so very 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 the products approved under MPI #46.
This enamel undercoat was thick enough to mask fine surface irregularities and fill the paper texture. It was inexpensive and offered the additional benefit of being 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 products, and a sandable, inexpensive, VOC-compliant replacement does not appear to exist. And 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.
The ASTM Level 5 Drywall Finish
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, unfortunately it’s no guarantee of a perfect finish.
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.”
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 and bumps, or other defects. Contrary to popular thinking, 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.”
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 “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 of the skim coat may also depend on how it 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 consistence is achieved.”
And in fact, with the joint compound skim coat materials currently on the market, there are three ways to apply them:
- 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, and after sanding, the paper texture often shows through, which essentially eliminates the value created by 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 versus Level 4
So what’s the solution? 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 intrepid 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 plus two coats that looked “okay” but not great will often look a whole lot better after its first repaint, when an additional two coats are applied.