What is Gypsum Board?
Gypsum board is the generic name for a family of panel-type products consisting of a noncombustible core, primarily of gypsum, with a paper surfacing on the face, back, and long edges.
Gypsum board is often called drywall, wallboard, or plasterboard and differs from products such as plywood, hardboard, and fiberboard, because of its noncombustible core. It is designed to provide a monolithic surface when joints and fastener heads are covered with a joint treatment system.
Gypsum is a mineral found in sedimentary rock formations in a crystalline form known as calcium sulfate dehydrate. 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. The crushed rock is then ground into a fine powder and heated to about 350 degreesF, driving off three fourths of the chemically combined water in a process called calcining. The calcined gypsum (or hemihydrate) is then used as 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 which 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 then cut to length and conveyed through dryers to remove any free moisture.
Gypsum manufacturers also rely increasingly on “synthetic” gypsum as an effective alternative to natural gypsum ore. The former is a by-product, or waste material, form other manufacturing processes, primarily the manufacture of titanium dioxide used in paint and the desulphurization of flue gases in fossil-fueled power plants. Located primarily in the eastern United States, these manufacturing or power-generating facilities are more than pleased to ship a steady stream of “production waste” to nearby gypsum board manufacturing facilities.
THE HISTORY OF GYPSUM BOARDToday’s gypsum board has as its predecessor a product called “Sackett Board,” a composite material made of layers of thin plaster placed between four plies of wool felt paper. The manufacturing process for Sackett Board was patented in 1894 by Augustine Sackett, the man generally considered to be the grandfather of the gypsum board manufacturing industry.
A sheet of Sackett Board was approximately ¼ inch thick and 36 inches square. It had open edges, which tended to erode, and the felt paper did not provide for a satisfactory wall finish. It was an excellent base for the application of gypsum plaster and it soon became a replacement for wooden slat lath in many geographic areas.
Concurrent with a rapid series of improvements in board manufacturing technology, gypsum board evolved between 1910 and 1930 into the finishable material that it is today. In 1910, a process for wrapping the board edges was created. This was 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.
Type ‘X’ gypsum board was first manufactured in the decade following World War II and improved type ‘X’ materials were introduced to the market during the 1960s and 1970s. Today, United States and Canadian market demands necessitate the manufacture of over 30 billion square feet of gypsum board on an annualized basis. Historical production statistics are contained in the Appendix.
ADVANTAGES OF GYPSUM BOARD CONSTRUCTIONGypsum board walls and ceilings have a number of outstanding advantages:
• Fire Resistive
• Sound Attenuation
• Durability
• Economy
• Versatility
Fire ResistiveGypsum 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.
For information about the use of gypsum board in fire-resistant construction systems consult GA-600, Fire Resistance Design Manual.Sound AttenuationControl of unwanted sound that might be transmitted to adjoining rooms is a key consideration in the design or renovation stage of a building or residence, taking into account the environment described for the particular activity of the occupants. Gypsum board wall and ceiling systems effectively 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.
DurabilityGypsum board is used to construct strong high quality walls and ceilings with excellent dimensional stability and durability. The surfaces are easily decorated and refinished.
EconomyGypsum board is readily available and easy to apply. It is an inexpensive wall surfacing material offering a fire-resistant interior finish. Both regular and pre-decorated gypsum board may be installed at relatively low cost. When pre-decorated board is used, further decoration is unnecessary.
VersatilityGypsum board satisfies a wide range of architectural requirements for design. Ease of application, performance, availability, ease of repair, and its adaptability to all forms of decoration combine to make gypsum board unmatched by any other surfacing product.
TYPES OF GYPSUM BOARD AND INDUSTRY TERMS
Developed through modern technology as a result of 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 occupancies; and to provide fire protection to structural elements. Most gypsum board is available with aluminum foil backing which provides an effective vapor retarder for exterior walls when applied with the foil surface against the framing.
Standard size gypsum boards are 4ft. 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 as follows:
• ¼-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.
• ½-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.
• ¾-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.
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.
In the 1940s different gypsum board formulations were investigated 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.” The basic components of type ‘X’ that give it a superior fire resistance are gypsum, glass fibers, and vermiculite.
In the 1960s, further modifications were made to the original successful type ‘X’ formulations of gypsum board used in some systems – particularly ceiling systems – without compromising the fire-resistive qualities. The new product demonstrates additional fire resistance over type ‘X’ core, and thus the term “improved type X” was coined.
Gypsum board products make up the predominant portion of a family of materials identified 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.
All individual materials within the gypsum board family are referenced in both a specific ASTM (spell out) 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 the criteria originally contained in approximately one dozen individual ASTM product standards, many of which have existed for many years.
Identified by their technically correct names, gypsum board products are as follows:
Gypsum Wallboard is produced primarily for use as an interior surfacing for buildings. It is the most often used commodity gypsum board and annually accounts for over 50 percent of all the gypsum board manufactured and sold in North America. Gypsum wallboard has a manila-colored face paper and is manufactured in a variety of thicknesses as both a regular- and a fire-resistant core material.
Gypsum Ceiling Board is an interior surfacing material with the same physical appearance as gypsum wallboard. Gypsum ceiling board is manufactured as a ½-inch thick material; it is designed for application on interior ceilings, primarily those intended to receive a water-based texture finish. It has a sag resistance equal to 5/8-inch thick gypsum wallboard.
Predecorated Gypsum Board has a decorative surface which 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 as both a regular- and a fire-resistant core material.
Water-resistant Gypsum Board is a 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 referred to as “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.
Gypsum Backing Board, Gypsum Coreboard, and
Gypsum Shaftliner Panel are all 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 is designed for use on the underside of eaves, canopies, carports, soffits, and other horizontal exterior surfaces that are indirectly exposed to the weather. It has 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 is used as a backing under exterior siding or cladding. It has a water-repellent face and back paper and can be manufactured with a water-resistant core. Depending on the thickness of the board, 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 has a distinctive blue-tinted face paper that is treated to facilitate the adhesion of thin coats of hard, high strength gypsum veneer plaster. It is produced in sheets that are 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.
5/8 TYPE X GYPSUM BOARD
When you want to go beyond basic requirements, 5/8” type X gypsum board is an excellent product for adding low-cost yet highly effective benefits to homes as well as commercial and other non-residential buildings. All gypsum board, including ½” regular wallboard, is naturally fire resistive. The increased thickness of 5/8” type X gypsum board offers additional protection and security to occupants.
LABELING AND THIRD-PARTY CERTIFICATION
For over 70 years, gypsum board has been accepted as a high performance, fire-resistive material. It is economical and easy to install and inspect. During this time, the gypsum industry has invested millions of dollars in research and development of new and improved products and systems as well as in fire-testing and product labeling programs. This voluntary investment in maintaining uniform standard provides gypsum board users a level of comfort that is not achievable with masonry materials whose fire-resistive properties are usually unknown. Today’s fire-rated gypsum boards are of superior quality and provide fire protection needed in modern construction. To ensure continuing quality of their products, gypsum board manufacturers subscribe to the following creed contained in GA-600, the Gypsum Association’s Fire Resistance Design Manual:
In order to maintain industry-wide quality assurance standards for gypsum board defined in this Manual as “type X” the Gypsum Association requires that any company listing proprietary tests or systems, or relying on the generic systems in this manual, shall subscribe to an on-going third-party, in-plant product inspection and labeling service. Additionally, member companies make annual written certification to the Gypsum Association that their products manufactured for use in systems listed in this Manual continue to be inspected and labeled by an independent third party testing service as listed on page 4.
The philosophical and technical reason for this voluntary industry-wide certification is to provide assurance to architects, builders, owners, occupants, and building officials that the type X gypsum board used in fire-resistance rated systems that appear in GA-600 has had its formulation and manufacturing process reviewed, monitored, and attested to by an approved independent third party. Code enforcement officials can easily determine the type and quality gypsum board used in fire-resistive systems.
Numerous fire-resistive systems that appear in the Gypsum Association’s Fire Resistance Design Manual, GA-600, are also listed in the UL Fire Resistance Directory and in the published directories of other approved certification and testing organizations where specific trade names, products, and manufacturers are detailed. The names and products of members of the Gypsum Association in the U.S. and Canada are listed in at least one of these nationally recognized authoritative sources of fire-resistive materials.
MOISTURE AND MOLD
In general, gypsum board should not be exposed to elevated levels of moisture for extended periods. Examples of elevated levels of moisture include, but are not limited to, exposure to rain, condensation, water leakage, and standing water. Some board exposed to these conditions may not need to be replaced, depending upon the source of the moisture and the condition of the gypsum board being considered for replacement. 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-231-03, Assessing Water Damage to Gypsum Board.
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. Observing these guidelines will help minimize the potential for mold growth on gypsum board. GYPSUM BOARD MUST BE KEPT DRY to prevent the growth of mold. For additional information on assessing water damaged gypsum board consult GA-238-03, Guidelines for Prevention of Mold Growth on Gypsum Board.
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. This test procedure was first published by ASTM in 1918 as ASTM C 19-18. That first ASTM version prescribed 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 that indicate the end of the endurance test. 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, one that is 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 also contains an optional method for the hose stream test. Under the optional program, which can only be used if both the testing laboratory and the test sponsor agree, 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, for example, needs to build only one test specimen, for that specimen will be subjected to both the fire endurance test and the hose stream test.
Consequently, a manufacturer attempting to obtain a 2-hour fire resistance rating for a wall system has two E 119 test options: they can construct two identical specimens of the intended system and subject the first specimen to the fire endurance test for two hours, and the second to the fire endurance test for one hour and the hose stream test for a prescribed period of time; or they can construct one specimen and subject it to the fire endurance test and the hose stream test. Each option is equally acceptable according to the test method; neither option is “better” than the other.
A fire resistance rating is one of many tools used by designers to assess relative fire risk. In addition to fire resistance, other properties of the construction materials to be considered include burning characteristics, fuel load of the space, and the proposed use of the structure or occupancy. Additional factors such as building location, distance to fire services, and the presence or absence of other fire protection systems are also part of 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 method that is conducted under laboratory condition 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. It may help to think of a fire resistance rating in the same way one thinks of the energy efficiency rating on a new appliance such as a water heater. The energy rating is determined under very specific test conditions; actual energy costs for the use of the appliance will likely be either more or less than the rating indicated on the sticker that is placed on the appliance.
GYPSUM BOARD AREA SEPARATION WALLS
Townhomes, apartments, and condominiums are popular choices for dwellings. Their unique design demands special methods of construction to provide safe, fire resistant, and acoustical separation between dwelling units. Gypsum board area separation wall systems have been specially 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. These wall systems have the additional advantage of all-weather, stable, sturdy construction, and they curtail the delays associated with temperature sensitive, labor intensive, and cumbersome masonry materials. Click here for more information on Gypsum Area Separation Walls.
GYPSUM BOARD ROOF UNDERLAYMENT
The use of 5/8 inch thick type X gypsum board as an underlayment of 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 tope of party walls.
Effectively preventing fire form penetrating through the roof eliminates updrafts, both limiting the potential for fire spreading on the roof surface and reducing the generation of flying brands. Adding gypsum board to roof systems also inhibits the spread of fire within an attic while protecting against burning brands from fires originating in another unit of from burning vegetation.
For more information on the use of 5/8 inch thick type X gypsum board as a roof underlayment, click on the attached link and review Gypsum Association Document GA-276.
ENVIRONMENTAL RESOURCES
The gypsum board manufacturers in the United States and Canada enthusiastically subscribe to the fundamental principles and core values inherent in protecting the environment and promoting environmental custodianship and stewardship. All manufacturers achieve this goal by promoting renewable energy sources, supporting technological research and development efforts, and educating employees as well as their communities.
When it comes to making good use of recycled materials or by-products from manufacturing operations, it’s hard to top the gypsum board industry.
More than 40 years ago, long before recycling became popular, the gypsum industry began recycling newsprint and other paper to manufacture the paper facing of gypsum board. Today, nearly 100 percent of the fiber used in the manufacture of gypsum board face and back paper comes from newsprint and post-consumer waste materials.
Gypsum manufacturers also rely increasingly on “synthetic” gypsum as an effective alternative to natural gypsum ore. The former is a by-product, or waste material, from other manufacturing processes, primarily the manufacture of titanium dioxide used in paint and the desulphurization of flue gases in fossil-fueled power plants. Located primarily in the eastern United States, these manufacturing or power-generating facilities are more than pleased to ship a steady stream of “production waste” to nearby gypsum board manufacturing facilities.
Other “green” sources of gypsum are production waste form the gypsum board manufacturing plants and board waste from new construction. Gypsum plants throughout the United States and Canada reclaim usable gypsum by feeding production overruns or materials damaged during production back into the manufacturing cycle. New construction gypsum waste is also reclaimed in some areas and is, after reprocessing, fed back into the board production cycle. More Info.
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