Webinar Q&A

High performance gypsum

Attendee questions

High Performance Gypsum: Protect Against Mold, Moisture and Exposure webinar on March 11, 2021
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Define exposure related to high-performance gypsum products.

Glass mat gypsum sheathing, Gold Bond® eXP® Fire-Shield® Sheathing, can be exposed up to 12 months against sun, wind, rain, etc. Interior glass mat products can be exposed up to 12 months against the elements when installed in a non-conditioned building.

Is an exterior vapor barrier on exterior sheathing required? Are taped joints required?

All buildings are required to have a water-resistive barrier such as 15 pound felt though many also act as air barriers. Vapor retarders are required by code depending on region. The air and water barrier manufacturer will specify joint treatment. For the protection of the gypsum panels, it is not necessary to tape the joints prior to the application of the air and water barrier.

Can glass mat sheathing serve as an air barrier if joints are taped?

Air barriers are systems of materials designed and constructed to control airflow between a conditioned space and an unconditioned space. The air barrier system is the primary air enclosure boundary that separates indoor (conditioned) air and outdoor (unconditioned) air. Gypsum panels are considered air barriers. The International Building Code (IBC) defines the air barrier as a continuous plane. National Gypsum believes that taping the joints on the gypsum sheathing meets the intent of the building code for an air barrier. An exterior sheathing application taped will provide about 20 perms of protection without addressing the transitions.

Does the fiberglass mat affect water vapor permeability?

No, the glass mat is vapor permeable. Our Gold Bond® eXP® Sheathing (1/2”) has a permeance of 22 perms and Gold Bond® eXP® Fire-Shield® Sheathing (5/8") is 19 perms.

Where high impact panels are used for interior applications, the tape joints are typically obvious once the walls are painted. How can this issue be resolved?

Gypsum abuse and impact panel products can have a shallower taper. It is imperative to have the tape coat pulled tight during application. A good quality primer and paint will also help better cover the tape joints.

Does the shaft wall panel calcify under heat?

It is recommended that all drywall products, including gypsum shaftliner, avoid exposure to temperatures exceeding 125° F for extended periods of time. See Gold Bond® eXP® Shaftliner for more details.

If gypsum board is exposed to fire, would it need to be replaced?

Any assembly directly exposed to the fire should be rebuilt. For fire-rated assemblies not exposed directly to the fire, it is always best to have a certified/licensed fire protection engineer or inspector assess the assembly and determine if it is still capable of performing as designed in a future fire.

What happens to unprotected roof coverboard if exposed to standing water over time?

Low-slope roof systems are intended to be installed, be water-tight or completed each day. Properly installed gypsum roof coverboards, like DEXcell® Roof Board, should not be exposed to moisture for any length of time. Ponding water on any gypsum board is not warranted.

What is the recommended edge treatment for cut edges using exterior sheathing?

Cut edges of fiberglass mat gypsum sheathing do not require treatment.

Can interior and exterior fiberglass mat boards be exposed to weather for up to 12 months?

Yes, interior and exterior fiberglass mat gypsum panels can be exposed for 12 months if installed in a vertical application. Gold Bond® eXP® Interior Extreme can be hung on the interior before the building is dried in.

What backer board materials may be installed for shower walls and ceilings when they are not used as a base for tile? Can water-resistant gypsum backing board be used in this application?

In the shower or tub surround, a code approved backer board (reference Table 2509.02 in the International Building Code) like Gold Bond® eXP® Tile Backer panels, PermaBASE® Cement Board or other product approved for "wet" areas are used for tile or non-tile applications in a shower or tub area. Water-resistant gypsum board, other than the glass mat tile backer panels, cannot be used in the wet area, per code. Outside the wet area moisture-resistant paper or glass mat gypsum products can be used, including in ceiling applications. Gold Bond® XP® Gypsum Board or Gold Bond® eXP® Interior Extreme Gypsum Panels can be used in non-wet areas.

Explain the difference between impact- and abuse-resistant interior gypsum board products.

Abuse-resistant gypsum board products, Gold Bond® XP® Hi-Abuse® Gypsum Board or Gold Bond® eXP® Interior Extreme AR Gypsum Panels, are abrasion or scratch resistant. Impact-resistant gypsum board products, Gold Bond® XP® Hi-Impact® Gypsum Board or Gold Bond® eXP® Interior Extreme IR Gypsum Panels, are also abrasion-resistant but are designed to stop penetration of impact into the cavity of the wall. Impact products will stop a baseball bat. See ASTM C1629 for more information.

Is a full skim coat required to finish the Gold Bond® eXP® Interior Extreme product? Is this product easy to cut?

Gypsum Association document GA-214-15 “Recommended Levels of Finish Gypsum Board, Glass Mat & Fiber-Reinforced Gypsum Panels” recommends skimming any glass mat interior product to a Level 5 finish in aesthetic areas and areas in critical lighting conditions. Gold Bond® eXP® Interior Extreme cuts and scores the same as paper faced gypsum board products.