ASTM C1177/C1177M-24

Standard Specification for Glass Mat Gypsum Substrate for Use as Sheathing

ABSTRACT
This specification covers the requirements for glass mat gypsum substrates designed to be used as exterior substrate or sheathing for weather barriers. The substrates shall consist of a noncombustible water-resistant gypsum core, surfaced with glass mat partially or completely embedded in the core. Materials shall be sampled, tested, and conform accordingly to specified physical property (flexural strength, humidified deflection, nail pull resistance, water resistance, and core, end, and edge hardness) and dimensional (thickness, width, length, end squareness, and edges) requirements.
SCOPE
1.1 This specification covers glass mat gypsum substrate, which is designed to be used as an exterior substrate for a weather barrier.  
1.2 The values stated in either SI units or inch-pound units are to be regarded separately as standard. Within the text, the SI units are shown in brackets. The values stated in each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in non-conformance with the standard.  
1.3 The text of this standard references notes and footnotes that provide explanatory material. These notes and footnotes (excluding those in tables and figures) shall not be considered as requirements of the standard.  
1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 31-Mar-2024
• ICS: 91.100.10 - Cement. Gypsum. Lime. Mortar
• Technical Committee: C11 - Gypsum and Related Building Materials and Systems
• Drafting Committee: C11.01 - Specifications and Test Methods for Gypsum Products

Relations

• Replaces: ASTM C1177/C1177M-17 - Standard Specification for Glass Mat Gypsum Substrate for Use as Sheathing
• Effective Date: 01-Apr-2024
• Referred By: ASTM C1397-13(2019) - Standard Practice for Application of Class PB Exterior Insulation and Finish Systems (EIFS) and EIFS with Drainage
• Effective Date: 01-Apr-2024
• Referred By: ASTM C1280-18(2023) - Standard Specification for Application of Exterior Gypsum Panel Products for Use as Sheathing
• Effective Date: 01-Apr-2024
• Referred By: ASTM C1535-05(2023) - Standard Practice for Application of Exterior Insulation and Finish Systems Class PI
• Effective Date: 01-Apr-2024
• Referred By: ASTM C1881-20 - Standard Guide for Closed-Loop Recycling of Scrap Gypsum Panel Products
• Effective Date: 01-Apr-2024
• Referred By: ASTM C1289-23a - Standard Specification for Faced Rigid Cellular Polyisocyanurate Thermal Insulation Board
• Effective Date: 01-Apr-2024
• Referred By: ASTM C1858-17a(2021) - Standard Practice for Design, Construction, and Material Requirements for Direct Hung Suspended T-bar Type Ceiling Systems Intended to Receive Gypsum Panel Products in Areas Subject to Earthquake Ground Motions
• Effective Date: 01-Apr-2024
• Referred By: ASTM C1516-05(2023) - Standard Practice for Application of Direct-Applied Exterior Finish Systems
• Effective Date: 01-Apr-2024
• Referred By: ASTM C1789-14(2018) - Standard Test Method for Calibration of Hand-Held Moisture Meters on Gypsum Panels
• Effective Date: 01-Apr-2024

Overview

ASTM C1177/C1177M-24: Standard Specification for Glass Mat Gypsum Substrate for Use as Sheathing provides the industry benchmark for glass mat gypsum substrates intended for use as exterior sheathing or substrate for weather barriers. Developed by ASTM Committee C11, this international standard outlines the requirements for noncombustible, water-resistant gypsum cores surfaced with a glass mat, which are designed to offer durability and resistance to fire, moisture, and mold in building envelope applications.

Glass mat gypsum sheathing has become a standard solution for supporting weather barriers, providing a stable base for exterior wall assemblies in commercial, institutional, and residential construction. The standard ensures consistent product performance through strict physical and dimensional property requirements.

Key Topics

• Material Composition
  • Specifies a noncombustible, water-resistant gypsum core per ASTM C22.
  • The core is surfaced with a glass mat that is partially or fully embedded.
• Product Types
  • Standard and Type X (fire-resistant) designations.
  • Type X substrate must meet minimum fire resistance ratings through ASTM E119 test methods.
  • Mold-resistant panels are evaluated to limit mold growth by ASTM D3273.
• Physical Properties
  • Requirements for:
    • Flexural strength (minimum breaking loads)
    • Humidified deflection limits
    • Core, end, and edge hardness
    • Nail pull resistance
    • Water resistance (maximum allowable water absorption)
• Dimensional Criteria
  • Controls thickness, width, length, end squareness, and edge/ends finish.
  • Nominal thickness options with standard tolerances ensure compatibility with building system requirements.

Applications

Glass mat gypsum substrates as defined by ASTM C1177/C1177M-24 are essential in the following construction scenarios:

• Exterior Sheathing
  • Provides a durable, stable substrate for weather barrier systems such as fluid-applied or sheet membranes.
• Fire-Resistant Assemblies
  • Type X panels support fire-resistance ratings required by building codes, making them suitable for exterior and interior assemblies demanding enhanced protection.
• Moisture and Mold Management
  • Frequently specified in high-humidity or precipitation-prone regions due to the core’s water-resistant and mold-resistant properties.
• Commercial & Institutional Buildings
  • Used in offices, hospitals, schools, and high-rise buildings for building envelopes.
• Residential Construction
  • Increasingly adopted in residential wood and steel-framed wall assemblies for superior weather protection.

Related Standards

Several ASTM standards are referenced or associated with ASTM C1177/C1177M-24, underpinning its comprehensive approach to product quality:

• ASTM C11 - Terminology Relating to Gypsum and Related Building Materials and Systems
• ASTM C22 - Specification for Gypsum
• ASTM C473 - Test Methods for Physical Testing of Gypsum Panel Products
• ASTM C645 - Specification for Nonstructural Steel Framing Members
• ASTM C1264 - Specification for Sampling, Inspection, Packaging, and Handling of Gypsum Panel Products
• ASTM D3273 - Test Method for Resistance to Mold on Surfaces
• ASTM E119 - Fire Tests of Building Construction and Materials

Practical Value

The adoption of ASTM C1177/C1177M-24 ensures:

• Consistent Performance: Manufacturers, contractors, and specifiers can rely on repeatable and verifiable properties for glass mat gypsum sheathing.
• Building Code Compliance: Supports project adherence to fire, structural, and weather barrier requirements, reducing liabilities and project risk.
• Quality Assurance: Sampling, inspection, marking, and certification processes embedded within the standard facilitate accountability throughout the supply chain.
• Global Applicability: Developed in accordance with international standardization principles, making it relevant to projects worldwide.

Keywords: glass mat gypsum sheathing, ASTM C1177, exterior substrate, weather barrier, fire resistance, mold resistance, building envelope, gypsum panel, construction standards

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: C1177/C1177M − 24
Standard Specification for
Glass Mat Gypsum Substrate for Use as Sheathing
This standard is issued under the fixed designation C1177/C1177M; the number immediately following the designation indicates the year
of original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval.
A superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope* and Storage of Gypsum Panel Products
D3273 Test Method for Resistance to Growth of Mold on the
1.1 This specification covers glass mat gypsum substrate,
Surface of Interior Coatings in an Environmental Cham-
which is designed to be used as an exterior substrate for a
ber
weather barrier.
E119 Test Methods for Fire Tests of Building Construction
1.2 The values stated in either SI units or inch-pound units
and Materials
are to be regarded separately as standard. Within the text, the
SI units are shown in brackets. The values stated in each
3. Terminology
system may not be exact equivalents; therefore, each system
3.1 Definitions shall be in accordance with Terminology
shall be used independently of the other. Combining values
C11.
from the two systems may result in non-conformance with the
3.2 Definitions of Terms Specific to This Standard:
standard.
3.2.1 weather barrier, n—a material that prevents the pas-
1.3 The text of this standard references notes and footnotes
sage of rain, sleet and snow.
that provide explanatory material. These notes and footnotes
(excluding those in tables and figures) shall not be considered
4. Materials and Manufacture
as requirements of the standard.
4.1 Glass Mat Gypsum Substrate shall consist of a noncom-
1.4 This international standard was developed in accor-
bustible water-resistant core, essentially gypsum complying
dance with internationally recognized principles on standard-
with Specification C22, surfaced with glass mat partially, or
ization established in the Decision on Principles for the
completely embedded in the core.
Development of International Standards, Guides and Recom-
4.2 Glass Mat Gypsum Substrate, type X (special fire-
mendations issued by the World Trade Organization Technical
resistant) designates glass mat gypsum substrate complying
Barriers to Trade (TBT) Committee.
with this specification that provide not less than 1-h fire
5 3
resistance rating for substrate ⁄8 in. [15.9 mm] thick or ⁄4-h
2. Referenced Documents
fire resistance rating for substrate ⁄2 in. [12.7 mm] thick,
2.1 ASTM Standards:
applied parallel with and on each side of load bearing 2 by 4
C11 Terminology Relating to Gypsum and Related Building
wood studs spaced 16 in. [406 mm] on center with 6d coated
Materials and Systems
nails, 1 ⁄8 in. [48 mm] long, 0.0915 in. [2.3 mm] diameter
C22 Specification for Gypsum
shank, ⁄4 in. [6.4 mm] diameter heads, spaced 7 in. [178 mm]
C473 Test Methods for Physical Testing of Gypsum Panel
on center with glass mat gypsum substrate joints staggered
Products
16 in. [406 mm] on each side of the partition and tested in
C645 Specification for Nonstructural Steel Framing Mem-
accordance with Test Methods E119.
bers
NOTE 1—Consult manufacturers for independent test data on assembly
C1264 Specification for Sampling, Inspection, Rejection,
details and fire resistance ratings for other types of construction. See fire
Certification, Packaging, Marking, Shipping, Handling,
test reports or listings from recognized fire testing laboratories for
assembly particulars, materials, and ratings.
4.3 Glass mat gypsum substrate, mold resistant, designates
This specification is under the jurisdiction of ASTM Committee C11 on
Gypsum and Related Building Materials and Systems and is the direct responsibility
gypsum panels having not more than 20 % mold growth, based
of Subcommittee C11.01 on Specifications and Test Methods for Gypsum Products.
on surface area coverage, when tested in accordance with Test
Current edition approved April 1, 2024. Published April 2024. Originally
Method D3273.
approved in 1991. Last previous edition approved in 2017 as C1177/C1177M – 17.
DOI: 10.1520/C1177_C1177M-24.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or 5. Physical Properties
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
5.1 Specimens shall be taken from the samples obtained in
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. accordance with Specification C1264.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C1177/C1177M − 24
5.2 Specimens shall be tested in accordance with Methods 6. Dimensions and Tolerances
C473.
6.1 Specimens shall be taken from the samples obtained in
5.2.1 Flexural Strength—The specimens shall be tested face
accordance with Specification C1264.
up and face down. The average breaking load shall not be less
6.2 Thickness, width, length and end squareness shall be
than the following:
determined in accordance with Test Methods C473.
Method B
6.2.1 Thickness—The nominal thickness shall be
1 7 1 5
⁄4 in., ⁄16 in., ⁄2 in., or ⁄8 in. [6.4 mm, 11.1 mm, 12.7 mm, or
Load, lbf [N] Bearing Load, lbf [N] Bearing edges
Thickness, edges perpendicular to parallel to the substrate
15.9 mm], with tolerances in the nominal thickness of 6 ⁄32 in.
in. [mm] the substrate edge edge
[60.8 mm], and with local variations of 6 ⁄16 in. [61.6 mm]
1 from the nominal thickness.
⁄4 [6.4] 50 [222] 40 [178]
⁄16 [11.1] 88 [394] 70 [314]
6.2.2 Width—The nominal width shall be up to 48 in.
⁄2 [12.7] 100 [445] 80 [356]
[1220 mm], with tolerance of ⁄8 in. [3 mm] under the specified
⁄8 [15.9] 140 [623] 100 [445]
width.
5.2.2 Humidified Deflection—Specim
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: C1177/C1177M − 17 C1177/C1177M − 24
Standard Specification for
Glass Mat Gypsum Substrate for Use as Sheathing
This standard is issued under the fixed designation C1177/C1177M; the number immediately following the designation indicates the year
of original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval.
A superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope*
1.1 This specification covers glass mat gypsum substrate, which is designed to be used as an exterior substrate for a weather
barrier.
1.2 The values stated in either SI units or inch-pound units are to be regarded separately as standard. Within the text, the SI units
are shown in brackets. The values stated in each system may not be exact equivalents; therefore, each system shall be used
independently of the other. Combining values from the two systems may result in non-conformance with the standard.
1.3 The text of this standard references notes and footnotes that provide explanatory material. These notes and footnotes
(excluding those in tables and figures) shall not be considered as requirements of the standard.
1.4 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
C11 Terminology Relating to Gypsum and Related Building Materials and Systems
C22 Specification for Gypsum
C473 Test Methods for Physical Testing of Gypsum Panel Products
C645 Specification for Nonstructural Steel Framing Members
C1264 Specification for Sampling, Inspection, Rejection, Certification, Packaging, Marking, Shipping, Handling, and Storage of
Gypsum Panel Products
D3273 Test Method for Resistance to Growth of Mold on the Surface of Interior Coatings in an Environmental Chamber
E119 Test Methods for Fire Tests of Building Construction and Materials
3. Terminology
3.1 Definitions shall be in accordance with Terminology C11.
3.2 Definitions of Terms Specific to This Standard:
This specification is under the jurisdiction of ASTM Committee C11 on Gypsum and Related Building Materials and Systems and is the direct responsibility of
Subcommittee C11.01 on Specifications and Test Methods for Gypsum Products.
Current edition approved Dec. 1, 2017April 1, 2024. Published December 2017April 2024. Originally approved in 1991. Last previous edition approved in 20132017 as
C1177/C1177M – 13.C1177/C1177M – 17. DOI: 10.1520/C1177_C1177M-17. 10.1520/C1177_C1177M-24.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C1177/C1177M − 24
3.2.1 glass mat, n—a mat of glass fibers with or without a binder.
3.2.2 edge, n—the bound edge as manufactured.
3.2.1 weather barrier, n—a material that prevents the passage of rain, sleet and snow.
4. Materials and Manufacture
4.1 Glass Mat Gypsum Substrate shall consist of a noncombustible water-resistant core, essentially gypsum complying with
Specification C22, surfaced with glass mat partially, or completely embedded in the core.
4.2 Glass Mat Gypsum Substrate, type X (special fire-resistant) designates glass mat gypsum substrate complying with this
5 3
specification that provide not less than 1-h fire resistance rating for substrate ⁄8 in. [15.9 mm] thick or ⁄4-h fire resistance rating
for substrate ⁄2 in. [12.7 mm] thick, applied parallel with and on each side of load bearing 2 by 4 wood studs spaced 16 in. [406
7 1
mm] on center with 6d coated nails, 1 ⁄8 in. [48 mm] long, 0.0915 in. [2.3 mm] diameter shank, ⁄4 in. [6.4 mm] diameter heads,
spaced 7 in. [178 mm] on center with glass mat gypsum substrate joints staggered 16 in. [406 mm] on each side of the partition
and tested in accordance with Test Methods E119.
NOTE 1—Consult manufacturers for independent test data on assembly details and fire resistance ratings for other types of construction. See fire test reports
or listings from recognized fire testing laboratories for assembly particulars, materials, and ratings.
4.3 Glass mat gypsum substrate, mold resistant, designates gypsum panels having not more than 20 % mold growth, based on
surface area coverage, when tested in accordance with Test Method D3273.
5. Physical Properties
5.1 Specimens shall be taken from the samples obtained in accordance with Specification C1264.
5.2 Specimens shall be tested in accordance with Methods C473.
5.2.1 Flexural Strength—The specimens shall be tested face up and face down. The average breaking load shall not be less than
the following:
Method B
Load, lbf [N] Bearing Load, lbf [N] Bearing edges
Thickness, edges perpendicular to parallel to the substrate
in. [mm] the substrate edge edge
⁄4 [6.4] 50 [222] 40 [178]
⁄16 [11.1] 88 [394] 70 [314]
⁄2 [12.7] 100 [445] 80 [356]
⁄8 [15.9] 140 [623] 100 [445]
5.2.2 Humidified Deflection—Specimens shall have an average deflection of not more than the following:
Thickness, Humidified deflection,
in. [mm] eighths of an in. [mm]
⁄4 [6.4] not required
⁄16 [11.1] 3 [9]
⁄2 [12.7] 2 [6]
⁄8 [15.9] 1 [3]
5.2.3 Core, End and Edge Hardness—Specimens shall have an average hardness of not less than 15 lbf [67 N] when tested in
accordance with Method B:
C1177/C1177M − 24
5.2.4 Nail Pull Resistance—Specimens shall have an average nail pull resistance of not less than the following when tested in
accordance with Method B:
Thickness, Nail pull r
...