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09 20 00: Plaster and Gypsum Board

by Gypsum Association (GA)

Last updated: 05-02-2008

Introduction

In 1888, Augustine Sackett used plaster of Paris sandwiched between several layers of paper to produce what would eventually become "Sackett Board," the original gypsum board.

By the 1950s, many innovations in gypsum board technology had been developed, including the listing of many fire-resistance rated designs, rounded edges, specialized nails, curved partitions, studless partitions, sound control systems, lightweight gypsum lath, plaster, and gypsum board systems that fueled a boom period for the use of gypsum products in both the residential and commercial construction industries. By 1955, an estimated 50 percent of new homes were built using gypsum wallboard. Lightweight gypsum board systems permitted the use of lightweight steel in steel framed buildings, which enabled the widespread growth of high-rise residential and commercial construction during the 1960s and 1970s.

Today gypsum board, along with a variety of other gypsum panel products, continues to serve as a preferred building material in both residential and commercial construction for interior walls and ceilings, exterior sheathing, fire-resistant partitions and membranes, and liner material for elevator shafts and stairwells. These properties make gypsum board well suited for building and space types requiring cost-effectiveness as well as fire resistiveness and maintainability.

Description

Gypsum is a common, naturally occurring, crystalline mineral found in sedimentary rock formations. Gypsum is also produced as a by-product of several industrial and manufacturing processes, the most common of which is flue-gas desulphurization of fossil fuel powered electrical generating plants, sometimes referred to as "synthetic gypsum." Both forms of gypsum are chemically the same—calcium sulfate dihydrate (CaSO4·2H2O). One hundred pounds of pure gypsum contains approximately 21 pounds of water chemically bound into the gypsum.

Gypsum paneled ceiling

Courtesy of Association of The Wall and Ceiling Industry

Naturally occurring gypsum rock (gypsum ore) is either mined or quarried and then crushed and ground to a powder whereas synthetic gypsum is generally provided as a finely ground damp material. Heating the powdered gypsum to about 350°F drives off any free moisture and much of the chemically combined water, thereby reducing the level of hydration. This process is known as "calcination." The calcined gypsum, commonly known as "plaster of Paris" or "stucco" and chemically defined as calcium sulfate hemihydrate (CaSO4·1/2H2O), is the principal ingredient in gypsum plaster.

Gypsum board is produced by combining calcined gypsum with water and other additives to form a slurry that is fed between continuous layers of paper on a board machine. As this "continuous" gypsum board moves along the conveyer line the calcium sulfate hemihydrate recrystallizes (rehydrates) to its original (dihydrate) rock state. The paper becomes chemically and mechanically bonded to the gypsum core. The gypsum board is cut to length and dried in kilns to remove excess moisture. Gypsum board is often referred to as drywall, wallboard, or plasterboard and differs from other common building materials such as plywood, hardboard, and fiberboard because of its noncombustible gypsum core. Gypsum board is the most commonly specified and installed interior finish material for walls and ceilings in North America.

Technically, gypsum board is defined as the generic name for a family of sheet products consisting of a noncombustible core, primarily of gypsum, with a paper surfacing on the face, back, and long edges. In recent years the family of gypsum-based panel materials has grown to include panel products other than those with the familiar paper facers. A number of specialized gypsum panel products and gypsum boards have been developed for specific uses which include:

Gypsum board systems with joints and fasteners finished with joint treatment material are designed to provide monolithic surfaces ready for decoration with paint, wallpaper, or other final decoration. Gypsum board wall and ceiling systems provide many outstanding advantages not available with other common interior finish materials:

Fire Resistance

Gypsum board is a high quality fire-resistive building material. It is the interior finish material of choice where fire-resistance ratings and low flame spread properties are required. When gypsum board is exposed to the elevated temperatures of a fire, the chemically combined water in its noncombustible gypsum core is released as steam, effectively retarding heat transfer. Even after complete calcination, when all the water has been released, the calcined gypsum continues to act as a barrier to heat and flame. Gypsum board is commonly specified for wall and ceiling finishes in buildings required to be of noncombustible or fire resistive construction. Gypsum board also has low flame spread and low smoke developed indexes making it one of the most fire-safe interior finish materials available today.

Sound Isolation

Preventing or minimizing the transmission of unwanted sound to and from adjoining rooms or from the outdoors is a prime consideration during the design phase of a building. Sound rated gypsum board wall and ceiling systems use single-layer and multi-layer applications to achieve specific Sound Transmission Class (STC) ratings and are key components in the effective control of sound transmission.

Serviceability

Gypsum board is used to construct strong, high-quality walls and ceilings with excellent dimensional stability and durability. Surfaces covered with gypsum board are easily redecorated and refinished as occupants and occupancies change and as decorating trends evolve.

Economy

Gypsum board is a minor factor in the overall cost of a building; it is readily available and easy to apply. Both gypsum wallboard and pre-decorated gypsum board are installed at relatively low cost when compared to other materials used in fire-resistive systems or as interior finishes. When pre-decorated gypsum board is used, further decoration is unnecessary.

Versatility/Flexibility

Gypsum board satisfies a wide range of architectural requirements for design and code compliance. Ease and speed of application, performance, availability, ease of repair, and adaptability to all forms of decoration combine to make gypsum board unmatched by any other interior finish material.

Environmentally Friendly

The North American gypsum industry has developed a responsible and environmentally conscious attitude toward issues of reclamation, preservation of natural resources, recycling and waste management, and otherwise protecting the environment. The industry has used recycled paper to manufacture gypsum board for nearly half a century. Over 90% of gypsum board paper used is from recycled materials. The gypsum industry increasingly uses "synthetic" gypsum to manufacture gypsum board. This raw material is a by-product, or waste material, from other manufacturing processes as well as the desulphurization of flue gases in fossil fuel power plants. By using what would otherwise be waste products, the gypsum industry reduces the stream of solid wastes going to landfills and at the same time extends natural gypsum reserves.

Application of Gypsum Board

A wide variety of gypsum board application methods are available to meet virtually any need in building design and construction. Gypsum board is applied in either single-layer or multi-layer systems to achieve specific fire or sound ratings. Gypsum board is applied over wood or steel framing or furring. It is also applied to masonry or concrete surfaces, either laminated directly or attached to wood furring strips or steel furring channels. Gypsum board ceilings can be directly attached to joists or trusses or attached to furring or grid systems suspended below structural members.

However, even the best gypsum board application cannot compensate for an inadequate or unsatisfactory substrate, or for extreme environmental conditions. Gypsum board will not straighten warped or twisted framing, nor will it smooth uneven masonry or concrete surfaces. The quality of gypsum board applications is largely dependent on the accurate alignment of the framing or furring to which the gypsum board is attached. Before application of the gypsum board begins, the framing or furring to which it is to be attached should be inspected for straightness, stability, and alignment. Warped or twisted wood framing or furring, or bent steel framing or furring, may cause joints to be misaligned or fasteners to pop and should be repaired or replaced. Green lumber or wood containing excessive moisture, over 15%, can result in fastener pops, joint misalignment, and cracking from warping or twisting as the wood dries.

Constructing a wall using gypsum board

Courtesy of Gypsum Association

All ends and edges of gypsum board except those oriented at right angles to framing members or furring should be located over framing members or other solid backing. Gypsum board is generally attached to the framing with nails, screws, or staples. Although nails are commonly used in wood frame construction, screws are often preferred because they are applied with automatic screw guns, have excellent holding power, and reduce the possibility of nail pops. A combination of nails and screws may also be used, with nails along edges and screws in the field. Staples are used because they are economical and can be quickly applied with staple guns; however, the use of staples should be limited to the base-layer in multi-layer systems or to gypsum sheathing on wood framing.

Gypsum board wall and ceiling surfaces are typically decorated with paint, texture, wallpaper, tile, or paneling. When pre-decorated gypsum board is used, joints are generally covered with matching molding or battens; no additional finishing or decoration is necessary.

Single-Layer Application

Single-layer gypsum board applications are the most common in light commercial and in residential construction. These systems rely on one layer of gypsum board attached to framing or furring. Although single-layer gypsum board systems are generally adequate to meet most minimum requirements for fire resistance and sound control, multi-layer systems are preferred for higher quality construction and to upgrade beyond the "bare minimums" of many code requirements.

Multi-Layer Application

Multi-layer systems have two or more layers of gypsum board and are used to meet higher sound and fire resistance requirements or to enhance these comfort and safety qualities beyond minimum code requirements. They also provide better surface quality because face layers can often be laminated over base layers eliminating many or all of the fasteners in the face layer. In addition, face-layer joints are stronger by virtue of the continuous backing provided by the base layers. Nail pops and ridging are less frequent and imperfectly aligned framing has less effect on the quality of the finished surface.

Emerging Issues

Mold and Moisture Dynamics has grown as an increasingly important design and specification concern with interior materials that have absorptive characteristics and are prone to mould and mildew problems. Materials such as interior fabrics, wood, carpets and paper based products—like gypsum board—must be properly installed, finished, and provided with adequately designed and operated climate control systems to avoid these problems.

As of December 1, 2004, a single ASTM International reference standard, ASTM C1396/C1396M-04, Standard Specification for Gypsum Board, has replaced eight standards previously used to designate specific gypsum board products employed in commercial and residential construction. No technical changes have been made to the individual specifications incorporated into C1396, which was established to avoid inadvertent inconsistencies in the requirements of individual products due to staggered document revision schedules.

Incorporated into the new ASTM C1396 Standard Specification for Gypsum Board are:

To facilitate a smooth transition from the old standards to the new, all-encompassing standard, the gypsum industry agreed in 1999 on a five-year phase-in period during which product labels and literature would project both the new standard and the original product specifications.

Now that the individual product standards have been withdrawn and replaced with a single standard, C1396, the building codes may soon reflect this change. Design professionals should make sure that their specifications use the C1396 designation instead of the previous standards so that they are in compliance with both industry standards and code language.

Relevant Codes and Standards

Guide Specifications

ICC—ES Evaluation Reports for Gypsum Board Materials

The Gypsum Association has received confirmation from ICC Evaluation Service, Inc. (ICC-ES) that Evaluation Report ESR-1338 (Gypsum Wall and Ceiling Assemblies) has been issued with an effective date of June 1, 2004,. This report describes requirements for fire-resistance- and sound- rated wall, floor-ceiling, and roof-ceiling assemblies composed of water-resistant gypsum backing board, gypsum wallboard, exterior soffit board, sheathing board, gypsum backing board and core board, or gypsum base for veneer plasters. ESR-1338 replaces ICBO-ES Report ER-1632, and also will be subject to re-examination in one year.

Of specific significance in this new report is language that allows the systems contained in the current edition (17th) of the Gypsum Association's publication GA-600-2003, Fire Resistance Design Manual, (FRDM) to be used to create fire-resistance-rated floor-ceiling, roof/ceiling, or wall assemblies. Previous evaluation reports had not kept pace with the most current edition of the FRDM and often made reference to outdated editions of the manual.

ASTM-International Standards

Industry Resources

Association of the Wall and Ceiling Industry (AWCI) Publications

Gypsum Association Publications

Trade Associations and other Organizations

WBDG Services Construction Criteria Base