Terminology

• Gypsum board / drywall / plasterboard: paper- or glass-mat-faced gypsum panel
• Plaster of Paris: calcined gypsum (hemihydrate) that sets when mixed with water
• Calcination: heating gypsum to drive off water, forming hemihydrate then anhydrite
• Type X: fire-rated gypsum board, such as 5/8 in. Type X in industry EPDs
• Glass-mat gypsum panel: gypsum core faced with glass mat, for sheathing and moisture-prone use
• GA-216: Gypsum Association application standard for gypsum panels
• Veneer plaster: thin plaster coat over a gypsum base

History and demand

First uses in construction

• Bronze Age Crete used gypsum in buildings when wood became scarce
• Alabaster gypsum was carved in ancient Egypt and Mesopotamia

Sourcing

• 2015 world gypsum production was about 258 million metric tons, China about 132 million

Composition and production

Raw materials

• Calcium sulfate dihydrate; Mohs hardness 1.5 to 2; specific gravity 2.31 to 2.33

Manufacturing process

• Heating in air drives off water, forming calcium sulfate hemihydrate (plaster) and then anhydrous calcium sulfate; adding water reverses the reaction and the plaster sets

Product forms

• Gypsum board, glass-mat gypsum panels, fiber-reinforced panels, sheathing, veneer base, lath, and plaster

Grades and types

• Gypsum board (ASTM C1396): standard interior panel
• Fiber-reinforced panel (ASTM C1278): fiber-reinforced gypsum
• Glass mat sheathing (ASTM C1177): exterior sheathing
• Glass-mat gypsum panel (ASTM C1658): glass-mat faced
• Backing panels for tile (ASTM C1178, C1288, C1325): glass mat, fiber-cement, and fiber-mat reinforced cementitious backer units

Properties

Physical

• Specific gravity (mineral): 2.31 to 2.33
• Hardness: Mohs 1.5 to 2

Fire behavior

• Glass fibers: added to gypsum board to improve fire resistance
• Fire-resistance ratings come from tested assemblies, not the material alone

Standards

Material specifications

• ASTM C1396: gypsum board
• ASTM C1278: fiber-reinforced gypsum panels
• ASTM C1177: glass mat gypsum sheathing
• ASTM C1658: glass mat gypsum panels
• ASTM C474 and C475: joint tape and joint compound
• ASTM C840 and GA-216: application and finishing of gypsum board
• ASTM C842, C843, and C926: gypsum plaster, veneer plaster, and cement plaster application

Uses in buildings

Building elements

• Metal Stud Walls: gypsum board sheathing and lining, counted as bracing in composite height
• Gypsum Board Ceilings: suspended and direct-applied board ceilings
• Interior Plaster: gypsum plaster and veneer plaster

Pros and cons

Pros

• Glass fibers improve fire resistance
• Available as board, sheathing, and tile-backing products
• Industry-wide EPDs available

Cons

• Water-sensitive: unsuitable for direct water exposure or continuous high humidity
• Mohs hardness of 1.5 to 2, a very soft mineral

Finishes and treatments

• Joint treatment: tape and compound (ASTM C474, C475) at joints and fasteners

Sustainability

Embodied carbon

• Gypsum Association industry-wide EPDs: 5/8 in. Type X board (EPD 10270, issued April 28, 2020, expired April 2026); glass-mat panels (EPD extended to November 1, 2026); new 1/2 in. lightweight and 5/8 in. Type X EPDs released June 2026; global warming values not retrieved

Manufacturing and cost

Main manufacturers and suppliers

• USG
• National Gypsum
• Georgia-Pacific Gypsum
• CertainTeed

Trade association: Gypsum Association.

Sources

• Wikipedia: Gypsum, https://en.wikipedia.org/wiki/Gypsum
• UpCodes: 2024 IBC Chapter 25 gypsum board, gypsum panel products and plaster, https://up.codes/viewer/department-of-defense/ibc-2024/chapter/25/gypsum-board-gypsum-panel-products-and-plaster
• Gypsum Association: frequently asked questions, https://gypsum.org/faqs/
• NSF: Gypsum Association Type X EPD 10270, https://info.nsf.org/Certified/Sustain/ProdCert/EPD10270.pdf
• Wikimedia Commons: Gypse Caresse.jpg, photo by Didier Descouens (CC BY-SA 4.0), https://commons.wikimedia.org/wiki/File:Gypse_Caresse.jpg