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Gypsum Board Frequently Asked Questions
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Callers to our 1-800-NATIONAL® Technical Assistance Hotline frequently ask the following questions about gypsum board:
 
 
Gypsum Board
What is the "R" Value for gypsum board?
What's the difference between "regular" and "Type X" gypsum board?
What's the difference between Gold Bond® Fire-Shield® and Gold Bond Fire-Shield C Gypsum Board?
What type of gypsum board would you recommend for use on the walls and ceiling of my indoor swimming enclosure?
My home was in a flood and the gypsum board in my basement was exposed to flood water. Do I have to replace the gypsum board in my basement?

What is the "R" Value for gypsum board?
For purposes of calculating "U" values, the "C" factor for 1" gypsum board is 1.2; Resistance "R" for 3/8" board is 0.32; for 1/2" board 0.45; for 5/8" board 0.56; and for 1" board 0.83.

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What's the difference between "regular" and "Type X" gypsum board?
ASTM C 36 designates two types of gypsum board, regular and Type X. Type X gypsum board, which is typically required to achieve fire resistance ratings, is formulated by adding noncombustible fibers to the gypsum. These fibers help maintain the integrity of the core as shrinkage occurs, providing greater resistance to heat transfer during fire exposure.

To receive the "Type X" designation under ASTM C 36, a gypsum board product must be shown to achieve not less than a one-hour fire resistance rating for 5/8" board or a 3/4-hour fire resistance rating for 1/2" board applied in a single layer, nailed on each face of load-bearing wood framing members, when tested in accordance with the requirements of ASTM E 119, Methods of Fire Test of Building Constructions and Materials.

Additionally, the Gypsum Association requires 1/2" Type X gypsum board be shown to achieve a one-hour fire resistance rating when applied to a floor ceiling system, as described by GA File Number FC 5410, in GA 600, the Gypsum Association Fire Resistance Design Manual.

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What's the difference between Gold Bond® Fire-Shield® and Gold Bond Fire-Shield C Gypsum Board?
For additional fire protection, National Gypsum Company manufactures Gold Bond Fire-Shield C products. Fire-Shield C products are formulated with a mineral core additive that expands when subjected to heat, which aids in holding the gypsum board together during fire exposure. Fire-Shield C Gypsum Board meets the Gypsum Association description of Improved Type X Gypsum Board—"specially formulated gypsum board, meeting all the requirements of Type X gypsum board, with additional properties to further enhance the fire resistive characteristics of the use of the product in some proprietary systems."

Gold Bond Fire-Shield C Gypsum Board may be used in designs requiring Fire-Shield (Type X core) of equal thickness, but Fire-Shield (Type X core) may not be substituted in designs that utilize Fire-Shield C (Improved Type X).

Gold Bond Fire-Shield is available in 5/8" thickness. Gold Bond Fire-Shield C is available in 1/2" or 5/8" thickness.

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What type of gypsum board would you recommend for use on the walls and ceiling of my indoor swimming enclosure?
None. Gypsum board (including green board) is NOT recommended for use where there will be direct exposure to water or continuous high humidity conditions such as found in saunas, steam rooms, gang shower rooms or swimming pool enclosures, per ASTM C890. A cementatious tile backer, such as PermaBase®, or the use of a Portland cement based plaster system should be considered.

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My home was in a flood and the gypsum board in my basement was exposed to flood water. Do I have to replace the gypsum board in my basement?
Yes, gypsum board that has been soaked by floodwater can be a permanent health hazard. When the gypsum board finally dries, there will still be mud and contaminants dried inside and to the gypsum board.

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