GYPSUM BOARD

                                       

                                                PROPERTIES OF GYPSUM BOARD

I. GYPSUM BOARD CONSTRUCTION
 
    What is Gypsum Board?
    Advantages of Gypsum Board Construction
    Ease of installation
    Fire resistance
    Sound isolation
    Durability
    Economy
    Versatility
    Types of Gypsum Board
    Limitations of Use
    Application of Gypsum Board
    Storage and Handling
    Jobsite Preparations
    Tools
    Application Sequence
    Cutting and Fitting Procedures
    Single-Ply and Multi-Ply Application
    Control Joints

I. GYPSUM BOARD CONSTRUCTION

WHAT IS GYPSUM BOARD?

Gypsum board is the generic name for a family of panel products that consist of a noncombustible core, composed primarily of gypsum, and a paper surfacing on the face, back and long edges. Gypsum board is one of several building materials covered by the umbrella term “gypsum panel products.” All gypsum panel products contain gypsum cores; however, they can be faced with a variety of different materials, including paper and fiberglass mats.

Gypsum board is often called drywall, wallboard, or plasterboard. It differs from other panel-type building products, such as plywood, hardboard, and fiberboard, because of its noncombustible core and paper facers. When joints and fastener heads are covered with a joint compound system, gypsum wall board creates a continuous surface suitable for most types of interior decoration.


Gypsum is a mineral found in sedimentary rock formations in a crystalline form known as calcium sulfate dihydrate CaSO4•2H2O. One hundred pounds of gypsum rock contains approximately 21 pounds (or 10 quarts) of chemically combined water. Gypsum rock is mined or quarried and transported to the manufacturing facility.

The manufacturer receives quarried gypsum, and crushes the large pieces before any further processing takes place. Crushed rock is then ground into a fine powder and heated to about 350 degrees F, driving off three-fourths of the chemically combined water in a process called calcining. The calcined gypsum (or hemihydrate) CaSO4•½H2O is then used as the base for gypsum plaster, gypsum board and other gypsum products.

Synthetic gypsum, commonly known as the FGD (Flue Gas Desulphurization) gypsum or DSG (desulphurised) gypsum may also be used in the production of gypsum board. This product is primarily derived from coal-fired electrical utilities which have systems in place to remove sulfur dioxide from flue gasses. These systems capture the sulfur dioxide by passing the gasses through scrubbers that contain limestone (calcium carbonate) which absorbs and chemically combines with the sulfur dioxide to form pure calcium sulfate, or gypsum. The synthetic gypsum is then transported to the gypsum board manufacturer; the production process for calcining synthetic gypsum is largely the same as with mined gypsum only no primary crushing is necessary.

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, chemically combining with the water that was removed during calcination and reverts 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.

Advantages of Gypsum Board Construction

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

    Ease of installation
    Fire resistance
    Sound isolation
    Durability
    Economy
    Versatility

Ease of installation

Gypsum board building systems are easy to install for several reasons. Gypsum board panels are relatively large compared to other materials. They come in 48- and 54-inch wide sheets and in lengths of 8, 10, or 12 feet, so they quickly cover large wall and ceiling areas. Gypsum board assemblies require only a few tools for their construction. Gypsum board can be cut with either a utility knife or a variety of saws, and it can be attached with a variety of fasteners, including screws, nails, and staples. It can also be adhesively attached to many substrates. Gypsum board is a lightweight material. Two workers can easily handle most panels and cover large areas in very short time periods. Gypsum board is easily finished using either a few hand tools or relatively modest machines. Gypsum board installers can quickly learn most application techniques in a few hours.

Fire resistance

Gypsum board is an excellent fire-resistive building material. In North America, it is the most commonly used interior finish where fire resistance classifications are required. Its noncombustible core contains nearly 21% chemically combined water, as described earlier, which, under high heat, is slowly released as steam. Because steam will not exceed 212 degrees F under normal atmospheric pressure, it very effectively retards the transfer of heat and the spread of fire. Even after complete calcination, when all the water has been released from its core, gypsum board continues to serve as a heat-insulating barrier. Moreover, tests conducted in accordance with ASTM E 84 show that gypsum board has a low flame-spread index and a low smoke-density index. When installed in combination with other materials in laboratory-tested wall and ceiling assemblies, gypsum board serves to effectively protect building elements from fire for prescribed time periods.

Sound isolation
                         
Preventing the transfer of unwanted sound to adjoining areas is a key consideration when designing a building, specifically when taking into account the intended activities of the occupants in the various parts of the building. For example, a building containing office spaces adjacent to manufacturing facilities requires more noise-reducing features than are typically necessary in a building that has only office space in it. Gypsum board wall and ceilings systems effectively help control sound transmission. Some construction techniques and gypsum board building systems that are successfully used for sound isolation and control are described and illustrated in Section VII.

Durability

Gypsum board is used to construct strong, high quality walls and ceilings that offer excellent dimensional stability and durability. Surfaces created using gypsum board are easily decorated and refinished.

Economy

Gypsum board is readily available and easy to apply. It is an inexpensive wall surfacing material that provides a fire resistant interior finish. Gypsum board building systems can generally be installed at significantly lower labor costs than most alternate systems.

Versatility

Gypsum board satisfies a wide range of architectural requirements for design. Ease of application, performance, ease of repair, availability, and its adaptability to all forms of decoration combine to make gypsum board unmatched by any other surfacing product.