Webinar Q&A

Finishing gypsum board

Attendee questions

Finishing Gypsum Board: Because Appearance Matters webinar on September 15, 2022
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How does the finishing of glass-mat panels differ from that of paper-faced gypsum board?

Glass-mat products, such as eXP Interior Extreme gypsum panels, are finished in the same manner as paper-faced gypsum board products except that a Level 5 finish is recommended for all interior glass-mat installations prior to paint application.

How thick is a skim coat typically; and can a skim coat be used to solve issues in a non-plumb wall?

A skim coat is very thin and not a solution for correcting issues in a non-plumb wall.

Does ASTM C840 include finishing of glass mat faced gypsum board?

ASTM C840 “Standard Specification for Application and Finishing of Gypsum Board” does not cover finishing glass-mat gypsum. The Gypsum Association document GA-214-2021 “Levels of Finish for Gypsum Panel Products” includes recommendations for finishing glass mat faced gypsum board products.

Is there a particular preference between the three types of joint compound for the Southwest, more specifically Arizona?

Our sales team reports that in this area it is common for contractors to use all-purpose ready mix for taping and then lite products for the additional coats.

Please clarify which level of finish is required for 1-hour fire-rated gypsum board wall assembly and what level of finish is required for a fire barrier? In addition, what is the difference between Level 1 and Level 2?

Both 1-hour fire-rated wall assemblies and fire barriers must be finished to Level 2. Per the GA-214-2021 “Levels of Finish for Gypsum Panel Products,” Level 1 requires taping the joints and angles only. This does not meet fire-rated requirements. Level 2 requires taping the joints, angles, and any penetrations (nails). Level 2 meets the requirements for fire-rated assemblies.

Are the joints and surfaces sanded after each application? For example, for Level 4, is sanding required after each applied layer?

If the joints are flat and smooth no sanding is required between each level of finish. If the joints are not flat and smooth, then sanding would be necessary. Most professional finishers do not sand joints between each level.

Considering less experienced finishers and reduced craftsmanship, please elaborate on how a Level 5 surface is achieved and what architects should review when participating in jobsite inspections at the finishing stage?

Level 5 will be a very thin skim coat of joint compound. The purpose of a skim coat is to equalize paint porosity and not to create a perfectly flat wall. The GA-214-2021 document describes in detail how a Level 5 finish is achieved and the appropriate inspection criteria. In addition, the Drywall Finishing Council provides inspection recommendations.

Several of the presentation photos showed gypsum board installed prior to windows or storefront installations. This is becoming the standard practice on many projects. How do standards address this and what future problems could occur based on this practice?

Standards like ASTM C840 “Standard Specification for Application and Finishing of Gypsum Board,” the International Building Code (IBC) and the GA-216-2021 “Application and Finishing of Gypsum Panel Products” do not allow the installation of paper-faced gypsum board products until “weather protection” is provided. Glass mat products such as our family of eXP products can be installed before the project is enclosed and can exposed and warranted for up to 12 months. The images shown in the presentation were included as examples of installations that are not allowed per ASTM and IBC. Explanations as to why the installation of paper-faced gypsum products should be avoided prior to the building being “dried in” or “weather tight” were reviewed.

Can a “ding” in a corner bead be repaired or does it need to be replaced?

There are several types of corner protection available: metal, plastic, and paper-faced metal. It is a best practice to remove and replace damaged metal corner bead. Consider using plastic corner beads to reduce the risk of damaged material.

Please clarify when to use setting type vs. drying type joint compounds.

This blog post outlines the differences between setting type and ready-mix joint compounds and when to use each.