What is Gypsum Board?

Gypsum board is the generic name for a family of panel-type products consisting of a noncombustible core, primarily composed of gypsum, with a paper surfacing on the face, back, and long edges. Often called drywall, wallboard, or plasterboard, gypsum board’s noncombustible core makes it different from  plywood, hardboard, and fiberboard. When joints and fastener heads are covered with a joint treatment system, gypsum board provide a monolithic surface that is ready for decorative treatment.

Gypsum is a mineral found in sedimentary rock formations in a crystalline form known as calcium sulfate dihydrate. One hundred pounds of gypsum rock contains approximately 21 pounds (or 10 quarts) of chemically combined water. Gypsum rock is mined or quarried and then crushed. In a process called calcining, the crushed rock is ground into a fine powder and heated to about 350 degrees F, driving off three fourths of the chemically combined water. The calcined gypsum (or hemihydrate) becomes the base for gypsum plaster, gypsum board and other gypsum products.

To produce gypsum board, the calcined gypsum is mixed with water and additives to form a slurry that is fed between continuous layers of paper on a board machine. As the board moves down a conveyer line, the calcium sulfate recrystallizes or rehydrates, reverting to its original rock state. The paper becomes chemically and mechanically bonded to the core. The board is cut to length and conveyed through dryers to remove any free moisture.

Gypsum manufacturers also increasingly rely on “synthetic” gypsum as an effective alternative to natural gypsum ore. Synthetic gypsum is a byproduct primarily from the desulfurization of the flue gases in fossil-fueled power plants.

Additional information on synthetic gypsum board.

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The History of Gypsum Board

The predecessor today’s gypsum board was called “Sackett Board,” a composite material made of layers of thin plaster placed between four plies of wool felt paper. The manufacturing process was patented in 1894 by Augustine Sackett, now considered the grandfather of the gypsum board manufacturing industry.

A sheet of Sackett Board was approximately 1/4 inch thick and 36-inches square. Its open edges tended to erode and the felt paper did not provide for a satisfactory wall finish. However, it was an excellent base for the application of gypsum plaster and in many geographic areas, Sackett Board became a replacement for wooden slat lath.

A rapid series of improvements in board manufacturing technology between 1910 and 1930 resulted in the finishable material gypsum board is today. In 1910, a process for wrapping the board edges was created, followed in short succession by the elimination of the two inner layers of felt paper, the replacement of the exterior facings with paper-based coverings, the creation of air-entrainment technology to make board lighter and less brittle, and the evolution of joint treatment materials and systems.

In the 1940s, manufacturers sought to increase the naturally occurring fire resistance of regular core gypsum board. A new product was eventually introduced that clearly demonstrated “eXtra” fire resistance, hence the name “type X.” Gypsum, glass fibers, and vermiculite are the components of type ‘X’ that provide superior fire resistance.

Further modifications to the original  type ‘X’ were made in the 1960s.  The formulations of gypsum board used in some systems – particularly ceiling systems –were improved without compromising the fire-resistive qualities. The new product demonstrated additional fire resistance over type ‘X’ core, and thus the term “improved type X” was coined.

To meet market demand in the United States and Canada, each year over 20 billion square feet of gypsum board is manufactured.

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Advantages of Gypsum Board Construction

Gypsum board walls and ceilings have a number of outstanding advantages:

  • Fire Resistive
  • Sound Attenuating
  • Durable
  • Economical
  • Versatile

Fire Resistive

Gypsum board is an excellent fire resistive material. It is the most commonly used interior finish where fire resistance classifications are required. Its noncombustible core contains chemically combined water which, under high heat, is slowly released as steam, effectively retarding heat transfer. Even after complete calcination, when all the water has been released, it continues to act as a heat insulating barrier. In addition, tests conducted in accordance with ASTM E 84 show that gypsum board has a low flame spread index and smoke density index. When installed in combination with other materials it serves to effectively protect building elements from fire for prescribed time periods.

The fire resistance of gypsum board can be described using three distinct terms: regular core, type ‘X’ core and improved type ‘X’ core. Regular core gypsum board is made of a noncombustible core material composed mainly of gypsum. Although it does not have the specially enhanced fire-resistive properties of type ‘X’, regular core gypsum board affords a degree of natural fire resistance.

For information about the use of gypsum board in fire-resistant construction systems consult GA-600, Fire Resistance Design Manual.

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Sound Attenuation

Control of unwanted sound transmission to adjoining rooms is a key consideration in the design or renovation stage of a building or residence. Gypsum board wall and ceiling systems help control sound transmission. Suggested systems for sound attenuation and sound control are described and illustrated in GA-600, Fire Resistance Design Manual along with recommended procedures to obtain sound control.


Using gypsum board results in strong high-quality walls and ceilings with excellent dimensional stability and durability. The surfaces are easily decorated and refinished.


Gypsum board is readily available and easy to apply. It is an inexpensive wall surfacing material offering a fire-resistant interior finish.


Gypsum board satisfies a wide range of architectural design requirements. Ease of application and repair, high performance, widespread availability, and decorative adaptability combine to make gypsum board an unmatched surfacing product.

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Types of Gypsum Board and Industry Terms

Gypsum board products are the largest group in the family of materials known as gypsum panel products. Gypsum panel products are defined as sheet materials consisting essentially of gypsum. They can be faced with paper or another material, or may be unfaced. Gypsum board, glass-faced sheathing materials with a gypsum core, and unfaced gypsum-based products are all considered to be gypsum panel products.

Developed through modern technology to meet specific requirements, gypsum board is mainly used as the surface layer of interior walls and ceilings; as a base for ceramic, plastic, and metal tile; for exterior soffits; for elevator and other shaft enclosures; as area-separation walls between building units; and to provide fire protection for structural elements. Most gypsum board is available with aluminum foil backing that provides an effective vapor retarder for exterior walls when the foil surface is applied against the framing.

Standard size gypsum boards are 4-ft. wide and 8, 10, 12, or 14-ft. long. The width is compatible with the standard framing of studs or joists spaced 16-in. and 24-in. on center. Some thicknesses and types of gypsum board are also produced as a standard 54-in. width material. Other lengths and widths are available as special order materials.

The various thicknesses of gypsum board available in regular, type X, improved type X, and pre-decorated board are::

  • 1/4-in. A low cost gypsum board used as a base in a multi-layer application for improving sound control, or to cover existing walls and ceilings in remodeling.
  • 5/16-in. A gypsum board used in manufactured housing.
  • 3/8-in. A gypsum board principally applied in a double-layer system over wood framing and as a face layer in repair or remodeling.
  • 1/2-in. Generally used as a single-layer wall and ceiling material in residential work and in double-layer systems for greater sound and fire ratings.
  • 5/8-in. Used in quality single-layer and double-layer wall systems. The greater thickness provides additional fire resistance, higher rigidity, and better impact resistance.
  • 3/4-in. Used in a similar manner to 5/8-in.
  • 1-in. Used in interior partitions, shaft walls, stairwells, chaseways, area separation walls and corridor ceilings. Manufactured only in 24 in. wide panels and usually installed as an integral part of a system.

Depending on the type and the use, gypsum board is manufactured with a tapered, square, beveled, rounded, or tongue and groove edge. Some gypsum board types may incorporate a combination of different edge types.

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All individual materials within the gypsum board family are referenced in both a specific ASTM manufacturing standard and in the global ASTM manufacturing standard for gypsum board, ASTM C 1396. Standard C 1396 was created in 1998 and is a compilation of criteria originally contained in approximately one dozen individual ASTM product standards, many of which prevailed for decades.

Identified by their technically correct names, gypsum board products are as follows:

Gypsum Wallboard
Primarily used as an interior surfacing for buildings and accounts for more than 50 percent of all gypsum board manufactured and sold in North America, annually. Gypsum wallboard has a manila-colored face paper and is manufactured in a variety of thicknesses with regular- and fire-resistant core materials.
Gypsum Ceiling Board
Interior surfacing material with the same physical appearance as gypsum wallboard. Gypsum ceiling board is manufactured as a 1/2-inch thick material designed for application on interior ceilings–primarily ceilings to receive a water-based texture finish. Gypsum ceiling board’s sag resistance is equal to 5/8-inch thick gypsum wallboard.
Predecorated Gypsum Board
A decorative surface that does not require further treatment. The surfaces may be coated or painted, printed, textured, or have a film – such as vinyl wallcovering – applied. It is manufactured in a variety of thicknesses, with both regular- and fire-resistant core materials.
Water-resistant Gypsum Board
Designed for use on walls primarily as a base for the application of ceramic or plastic tile. It is readily identified by its green-tinted face paper and is commonly called “Greenboard.” It has a water-resistant core and a water-repellent face and back paper; it is generally installed in bath, kitchen, and laundry areas where allowed by applicable code.
Gypsum Backing Board, Gypsum Coreboard, and Gypsum Shaftliner Panel
Designed to be used as base materials in multi-layer, solid and semi-solid, and shaftwall systems. Gypsum backing board is used as a base layer for other gypsum board materials in systems or as a base for dry claddings such as acoustic tile. Gypsum coreboard and gypsum shaftliner are manufactured with a type X core, using a specific edge configuration to facilitate installation into specialized stud systems and a type X core.
Exterior Gypsum Soffit Board
Designed for use on the underside of eaves, canopies, carports, soffits, and other horizontal exterior surfaces that are indirectly exposed to the weather. Its water-repellent face and back paper and is more sag-resistant than regular wallboard. Exterior gypsum soffit board can be manufactured with a type X core and typically has a light brown face paper.
Gypsum Sheathing Board
Used as a backing under exterior siding or cladding. Features a water-repellent face and back paper and can be manufactured with a water-resistant core. Depending on thickness, gypsum sheathing board is manufactured with either a square or a tongue-and-groove edge and a fire-resistive core. It generally has a brown or light black face paper.
Gypsum Base for Veneer Plaster
A distinctive blue-tinted face paper treated to facilitate adhesion of thin coats of hard, high-strength gypsum veneer plaster. Produced in sheets the same width as gypsum wallboard and can be manufactured with a fire-resistive core.

Gypsum Association member companies also produce other specialized gypsum panel products. Specific information on these materials should be obtained directly from the manufacturer.

For additional information, please see our publication GA-223-04, Gypsum Panel Products Types, Uses, Sizes, and Standards.

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Labeling and Third-Party Certification

For over 90 years, gypsum board has been accepted as a high performance, economical and easy to install and inspect fire-resistive material. During this time, the gypsum industry has invested in research and development of new and improved products and systems as well as fire-testing and product labeling programs. This voluntary investment in maintaining uniform standards results in fire-rated gypsum boards of superior quality. To maintain industry-wide quality assurance standards, member companies make annual written certification to the Gypsum Association that their products continue to be inspected and labeled by an independent third-party testing service.

There are both ethical and technical reasons for this voluntary industry-wide certification.  The Association’s Fire Resistance Design Manual, GA-600 details more than 600 fire-resistance rated systems.  It is essential that the type X gypsum board used in these systems have formulation and manufacturing process that are reviewed, monitored, and attested to by an approved independent third party. Architects, builders, owners, occupants, building  code enforcement officials rely on the Fire Resistant Design Manual  for specification and fire resistance ratings for more 600 systems that may be used for fire-rated walls and partitions, floor/ceiling and roof/ceiling assemblies and to protect columns, beams and girders.

Many fire-resistive systems that appear in the Gypsum Association’s Fire Resistance Design Manual are also listed in the UL Fire Resistance Directory and are reference by the ICC, the National Fire Codes as well as many state and local jurisdictions in the United States and Canada.

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Basics of Gypsum Board Fire Testing

The fire resistance test method used throughout the United States is ASTM E 119, Standard Test Methods for Fire Tests of Building Construction and Materials. ASTM prescribes two tests:

  1. A fire endurance test.
  2. A fire and fire stream test (commonly referred to as the hose stream test).

Similar test methods are published by Underwriters Laboratories and by the National Fire Protection Association.

The fire endurance test subjects a specimen to a prescribed fire until certain conditions are met. This period of time is known as the “resistance period” of the fire endurance test. All fire resistance rated systems, regardless of the materials from which they are built, are tested using this test.

The hose stream test subjects a duplicate specimen, identical to the fire endurance tested sample, to a fire exposure test “for a period equal to one half of…the resistance period of the fire endurance test, but not for more than one hour” and to the impact, cooling and erosion effect of a stream of water directed from a fire hose. If no significant amount of water passes through the duplicate test specimen, the resistance period time established by the fire endurance test sample becomes the fire rating for the system.

The hose stream test is conducted only on wall systems. The E 119 test method does not require it to be conducted on column, ceiling, beam, or girder systems.

The E 119 test method provides an optional method for the hose stream test. The optional program can be used only if both the testing laboratory and the test sponsor agree.  In this case, the hose stream is administered to the same specimen used for the full fire endurance test without the need for—and added cost of—constructing and burning a duplicate specimen as is required by the primary language. A manufacturer using the optional hose stream method builds one test specimen that is subjected to both the fire endurance test and the hose stream test: Each option is equally acceptable.

A fire resistance rating is one of many tools used by designers to assess fire risk. Fuel load of the space, proposed use of the structure or occupancy are additional considerations. Building location, distance to fire services, and the presence or absence of other fire protection systems are also pertinent factors in this complex assessment process.

A fire resistance rating alone cannot predict the performance of a system or building in an actual fire. In fact, no fire test conducted under laboratory conditions can predict what will happen in a real structure fire. Fire tests are simply convenient ways of classifying materials and establishing a ranking of performance among different materials so designers can compare and select materials and systems for specific projects.

Fire test results – including fire resistance ratings – enable code officials to compare materials and systems against code requirements to determine compliance. A fire resistance rating is similar to an energy efficiency rating on a new appliance. The energy rating is determined under very specific test conditions; actual energy costs will vary based on other factors including how many people use the appliance and under what conditions.

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Gypsum Board Area Separation Walls

Townhomes, apartments, and condominiums are popular housing choices. Multi-family housing demands special methods of design and construction to provide safe, fire resistant, and acoustical separation between units. Gypsum board area separation wall systems are specifically developed to protect the occupants of attached and multiple unit residences. These walls also provide code-compliant, lightweight, efficient, and cost effective assemblies for builders and owners.

Read more about Gypsum Area Separation Walls.

Gypsum Board Roof Underlayment

The use of 5/8-inch thick type X gypsum board as an underlayment for combustible roofs in multi-family construction is the preferred alternate to roof parapets separating dwelling units. This method of fire protection is designed to resist the spread of fire from unit to unit over the top of party walls. Adding gypsum board to roof systems prevents fire from penetrating through the roof, eliminates updrafts, limits the potential for fire spread on the roof surface and reduces flying brands.

For more information on the use of 5/8 inch thick type X gypsum board as a roof underlayment review Gypsum Association Document GA-276.

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Moisture And Mold

Gypsum 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. In general, gypsum board should not be exposed to elevated levels of moisture for extended periods. Avoid exposure to rain, condensation, water leakage, and standing water. Depending upon the source of the moisture and the condition of the gypsum board, some board exposed to these conditions may not need to be replaced. However, IF THERE IS EVER A DOUBT ABOUT WHETHER TO KEEP OR REPLACE GYPSUM BOARD THAT HAS BEEN EXPOSED TO MOISTURE – REPLACE IT. For additional information on assessing water damaged gypsum board consult GA-231-06, Assessing Water Damage to Gypsum Board.

GYPSUM BOARD MUST BE KEPT DRY to prevent the growth of mold. Minimize the potential for mold growth on gypsum board. Consult GA-238-03, Guidelines for Prevention of Mold Growth on Gypsum Board.

Environmental Resources — Gypsum Sustainability

Gypsum board manufacturers in the United States and Canada subscribe to the fundamental principles of sustainability and environmental stewardship. Manufacturers promote renewable energy sources, support technological research and development efforts, and educate employees as well as their communities on the importance of a responsible and holistic approach to the built and natural environments.

Read more about gypsum and sustainability.

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