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M-GLASS® Exterior Sheathing

M-Glass Exterior Sheathing is a high performance mold and moisture resistant panel designed for direct attachment to exterior side-wall and soffit framing as a underlayment for various exterior materials such as wood, metal or vinyl siding, properly detailed Exterior Insulation Finish Systems (EIFS), masonry veneer, stucco, shingles, etc. It is produced in 1/2” and 5/8” thicknesses with the 5/8” M-Glass Exterior Sheathing having a UL classified formulated Type X core for use in approved fire rated assemblies.

American Gypsum products contain no asbestos and no detectable levels of formaldehyde

Basic Uses

American Gypsum’s M-Glass Exterior Sheathing is manufactured to meet or exceed the requirements of ASTM C1177, and was developed for and is backed by a limited warranty for exposure up to 12 months under normal weather conditions on commercial and residential projects. M-Glass Exterior Sheathing provides mold, moisture and fire resistance protection when attached directly to exterior side-wall or soffit framing

for use as a underlayment for finishes such as wood, metal or vinyl siding, properly detailed Exterior Insulation Finish Systems (EIFS), masonry veneer, stucco, shingles, etc.

Product Data


ThicknessWidthsLengthsEdge Types
1/2" (12.7mm) 4’ (1219mm) 8’ (2438mm) Square
5/8” (15.9mm) 4’ (1219mm) 8’ (2438mm) Square

Special lengths or edges may be available on special order. Consult your American Gypsum sales representative for details.

Technical Data

Storage and Handling

M-Glass Exterior Sheathing board does not generate or support the growth of mold when it is properly transported, stored, handled, installed, and maintained. However, mold spores are present everywhere and when conditions are favorable; mold can grow on practically any surface. The panels must be stored off the ground and in an area that offers protection from adverse weather conditions, condensation, and other forms of moisture. Sufficient risers must be used to assure support for the entire length of the wallboard to prevent sagging. M-Glass Exterior Sheathing shall always be stacked flat - NEVER on edge or end. Panels stacked on edge or end are unstable and present a serious hazard should it accidentally topple. Care must be taken so weight is evenly distributed and floors are not overloaded.

Material must be protected during transit with a weather-tight cover in good condition. Plastic shipping bags are intended to provide protection during transit only and must be promptly removed upon arrival of the load. Failure to remove the shipping bag can increase the likelihood of developing conditions favorable to the growth of mold.

M-Glass Exterior Sheathing that has visible mold growth must not be used. For additional information refer to Gypsum Association publication, “Guidelines for the Prevention of Mold Growth on Gypsum Wallboard” (GA-238).

Applicable Standards

Mold Resistance

Score of 10 (ASTM D 3273)


ASTM C 1177


ASTM C 1280

Gypsum Association GA-253

Surface Burning Characteristics


Flame Spread 0

Smoke Developed 0


Non-Combustible (ASTM E 136)

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