Section I – Gypsum Board Construction
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I. GYPSUM BOARD CONSTRUCTION
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. A typical board application is shown in Figure 1.
Fig. 1 – Horizontally Applied Gypsum Wallboard Showing Joints and Framing
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.
Gypsum board walls and ceilings have a number of outstanding advantages:
- Ease of installation
- Fire resistance
- Sound isolation
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.
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.
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.
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.
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.
Fig. 2 – How Gypsum Retards Heat Transmission
Using ever-developing new technologies, gypsum producers offer a variety of gypsum board products for many specific applications, including: the surface layer of interior walls and ceilings; a base for ceramic, plastic and metal tile; exterior sheathing and soffits; elevator and other shaft enclosures; area separation fire walls between occupancies; and the fire-resistant layer over structural elements.
Regular and Type X gypsum board (described below) are available in several thicknesses. Different thicknesses are typically used in the specific following applications:
- ¼ -inch – A low cost gypsum board used as a base in a multilayer application for improving sound control, used to cover existing walls and ceilings in remodeling and for curved surfaces.
- 5/16 -inch – A specialty product primarily used in the production of manufactured housing and in laminated double thickness for special sound control panels.
- 3/8-inch – A gypsum board principally applied in a double-layer system over wood framing and as a face layer in repair or remodeling.
- ½-inch – 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-inch – Used in quality single-layer and double-layer wall systems. The greater thickness provides additional fire resistance, higher rigidity, and better impact resistance.
- ¾-inch & 1 inch – Used in interior partitions, shaft walls, stairwells, chaseways, area separation firewalls and corridor ceilings. Special edged panels are used in some interior partitions.
Standard size gypsum boards are 48 inches wide and 8, 10, 12 or 14 feet long. The 48 inch width is compatible with standard framing methods in which studs or joists are spaced 16 inches and 24 inches o.c. (Other lengths and widths of gypsum board are available from the manufacturer on special order.)
Edges available are rounded, tapered, beveled, square edge, and tongue and groove (V-edge).
Fig. 3 – Graphic of Edge Types
Common Types of Gypsum Board in Alphabetical Order:
- Abuse-resistant gypsum panels offer greater resistance to surface indentation, abrasion and penetration than standard gypsum panels.
- Eased edge gypsum board, which has a tapered and slightly rounded or beveled factory edge. It may be used as an aid in custom finishing of joints.
- Exterior gypsum soffit board is board designed for use on the undersides of eaves, canopies, carports, and other commercial and residential exterior applications with indirect exposure to the weather. Soffit board is available in 1/2 or 5/8 -inch thicknesses with both regular and Type X core.
- Foil-backed gypsum board has aluminum foil laminated to the back surface of regular gypsum board or other gypsum panel products. Foil-backed panels serve as vapor barriers.
- Gypsum base for veneer plaster serves as a base for thin coats of hard, high strength gypsum veneer plaster.
- Gypsum liner board serves as a liner panel in shaft walls, stairwells, chase ways, area separation fire walls, and corridor ceilings. It has a special fire-resistant core encased in moisture-resistant paper. Liner board is available in ¾ or 1 -inch thicknesses, widths of 24 or 48 inches and with square edges (sometimes eased square edges). Gypsum liner board is also available with fiberglass mat facing that increases its weather and mold resistance.
- Gypsum sheathing is used as a protective fire resistive membrane under exterior wall surfacing materials such as wood siding, masonry veneer, stucco and shingles. It also provides protection against the passage of water and wind and adds structural rigidity to the framing system. The noncombustible core is surfaced with water repellent paper; in addition, it may also have a water resistant core. Available in 2 feet and 4 feet widths, ½ -inch and 5/8 -inch thick. It is also available with Type X core. Gypsum sheathing is also available with a glass mat facing. This product is more weather resistant and mold resistant than paper-faced gypsum sheathing, and it is often used as a substrate for Exterior Insulating Finishing Systems (EIFS).
- Impact-resistant gypsum panels offer greater resistance to the impact of solid objects from high traffic and vandalism than standard gypsum panels.
- Mold-resistant board incorporates various methods of preventing the growth of mold and mildew on the board’s surface.
- Non-paper-faced gypsum board is unfaced or has a facing other than paper.
- Regular gypsum board (gypsum wallboard) is used as a surface layer on walls and ceilings.
- Sag-resistant board is a ceiling panel that offers greater resistance to sagging than regular gypsum products used for ceilings where framing is typically spaced 24 inches o.c.
- Type C or Proprietary Type-X gypsum board is available in ½ -inch and 5/8 -inch thicknesses and is required in some fire rated assemblies. Additional additives give this product improved fire resistive properties.
- Type X gypsum board is available in ½ -inch and 5/8 -inch thicknesses and has an improved fire resistance made possible through the use of special core additives. It is also available with a predecorated finish. Type X gypsum board is used in most fire rated assemblies.
- Water-resistant gypsum board has a water resistant gypsum core and a water repellent paper. It serves as a base for ceramic or plastic wall tile or plastic finish panels in non-wet areas. This product is available with a regular or Type X core and in ½ -inch and 5/8 -inch thicknesses.
Note: Do not use water-resistant gypsum board on ceilings or soffits unless extra framing is installed; do not exceed 12 inches o.c. between framing members. Do not use water-resistant gypsum board as a tile-backing substrate material where the final surface is directly exposed to running water; select one of several specialty products, including glass-mat-faced gypsum board or cement-based board, as a tile-backing substrate for areas directly exposed to running water.
For installation of gypsum board and finishes, maintain room temperature at not less than 40 degrees F for the mechanical application of gypsum board and not less than 50 degrees for the adhesive application of gypsum board and for joint treatment, texturing and decoration, unless recommended otherwise by the manufacturer. CAUTION: When using a temporary heat source, do not allow ambient temperatures to exceed 95 degrees F in any given room or area. Maintain adequate ventilation in the working area during installation and curing period. Do not use gypsum board where exposure to moisture is extreme or continuous. Take care to ensure that the gypsum board will not be exposed to temperatures exceeding 125 degrees F for extended periods of time, for example, when located adjacent to wood burning stoves, electric lighting, electric heating appliances or other heating units, or hot air flues.Note: Proper installation of lighting and other heat–producing electrical fixtures requires strict adherence to the National Electrical Code (NFPA 70A). When using gypsum board in air handling systems, keep the gypsum board surface temperature above the air stream dew point temperature but below 125 degrees F. Consult manufacturer’s literature for other limitations of use for specific products.
Gypsum board can be applied over wood or metal framing or furring. It can be applied to masonry and concrete surfaces, either directly or to wood or metal furring strips. When applying board directly to masonry or concrete surfaces, smooth or fill in any irregularities to ensure proper attachment and an acceptable final finished surface. Furring properly attached to interior sides of exterior walls provides flat surfaces for standard fastener application as well and sufficient separation from substrates to overcome dampness in exterior walls. Do not allow gypsum board to directly contact surfaces, such as concrete or soil, with potentially high moisture contents. Most common in residential construction is the gypsum wallboard system1in which the joints between the panels and internal corners are reinforced with tape and covered with joint compound to create a surface suitable for final decoration. External corners are normally reinforced with either a metal or plastic corner bead which in turn is covered with joint compound. Exposed edges are covered with metal or plastic trim. The result is a smooth, unbroken surface ready for final decoration of paint, textures, wallpaper tile, paneling, or other materials.1 See GA-216, Recommended Specifications for the Application and Finishing of Gypsum Panel Products.
Schedule the delivery of gypsum board to coincide with its installation. (Fig.4)
Fig. 4 – Boom Truck Delivering Board to Jobsite
Store boards or panels flat and protected from the elements. Be sure that materials used as storage supports (risers) are at least 4 inches in width and of uniform depth or length. As the units of gypsum board are tiered, align risers carefully from bottom to top so that the load of each tier is transferred directly to the next level of risers, thus avoiding sagging or otherwise distorting the plane of the boards.
Avoid stacking longer boards on shorter boards to prevent the longer boards from warping or breaking. Avoid leaning boards horizontally against vertical framing as they may shift and fall and in turn injure workers. Also avoid leaning boards during periods of high humidity or else the boards may warp. Remove shipping bags immediately after delivery to prevent the buildup of condensation. Keep materials protected from the weather until ready for use on the jobsite. Take care while moving boards not to drag them and damage their edges and corners.
Refer to Gypsum Association publication GA-801 “Handling and Storage of Gypsum Panel Products: A Guide for Distributors Retailers and Contractors” and GA-238, Guidelines For Prevention Of Mold Growth On Gypsum Board, for more detailed instructions. Also see Section IX.
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Ceilings finished with water-based spray texture finishes require special attention to the spacing of framing members, the thickness and type of gypsum board used, proper ventilation, placement of a vapor retarder, presence of insulation, and other items that can affect the performance of the system. Failure to follow recommendations for joist spacing, board application, vapor retarder and insulation placement may result in the sagging of the ceiling. During cold or damp weather, insulate before installing gypsum board on a ceiling with a vapor barrier.
The following table shows maximum framing spacing for gypsum board that is to be covered with water-based texturing materials:
(Note: 1/2-inch ceiling board may be applied perpendicular to framing spaced at 24″ o.c.)
Table I – with framing spacing for textured gypsum board ceilings per board thickness
Keep lumber dry during storage and installation at the jobsite. Avoid using lumber with a moisture content exceeding 15 % at the time of the gypsum board application. Avoid using “green lumber” –which may contain up to 19% moisture at the time of sale – for framing. When green lumber is used, screw attachment of gypsum board reduces the chances of fastener fastening problems. Because lumber shrinks across the grain as it dries, it tends to expose the shanks of nails driven into the edge of the framing members.
Fig. 5 – Stud
Shrinkage with Reduction in Moisture Content
If framing shrinkage is substantial or nails are longer than necessary, the gypsum board may separate from its framing lumber, which often causes nail heads to protrude above the board surface (these blemishes are colloquially known as “nail pops”).
Gypsum board installation and finishing require only some basic tools. While there are also many specialized hand and power tools available for gypsum board installation, here’s a list with brief descriptions of the basic tools necessary for a typical wallboard job:
Measuring tape – A steel retractable measuring tape, usually 25 feet in length.
Gypsum board T-square –Square edge for measuring and cutting gypsum board to length and for cutting out holes for square outlet boxes and other openings.
Utility knife – Standard cutting tool with replaceable/reversible blades for scoring and cutting gypsum board.
Hammer – Drives nails through gypsum board into wood framing.
Keyhole saw – Small triangular saw for cutting out holes for outlet boxes, pipes, and other penetrations.
Rasp – A tool for smoothing rough edges of wallboard after it has been scored and snapped.
Assorted trowels and taping knives – Bladed tools for applying and smoothing tape and joint compound over joints and fastener heads.
Mud tray – Box to contain joint compound while finishing joints and fastener heads.
Sanding pole – Tool that enables sanding walls from floor to ceiling and standard height ceilings without the use of a ladder.
Screw gun – Power tool that drives all types of gypsum board screws through gypsum board and into framing or substrate.
Use the following procedures to ensure a successful gypsum board application:
1. Install ceiling panels first, then the wall panels.
2. Once cut to size, position gypsum boards into place without forcing them.
3. Match similar edges and ends, i.e.: tapered to tapered, square-cut ends to square ends.
4. Plan to span the entire length of ceilings or walls with single boards if possible to reduce the number of butt joints, which are more difficult to finish. Stagger butt joints and locate them as far from the center of the wall and ceiling as possible so they will be inconspicuous.
5. In a single-ply application, position all board ends and edges over parallel framing members to ensure that the joints are supported. (Exception: In a two-ply assembly, with adhesive between the plies, the ends and edges of face layers need not fall on supporting members.
Take care to install mechanical and electrical equipment at the proper distance relative to the framing to allow for the gypsum board thickness so that the trim components, such as cover plates, registers, and grilles, fit correctly. Do not allow the depth of electrical boxes to exceed the framing depth and avoid placing boxes on opposite sides of a wall in the same stud cavity space. Avoid having electrical boxes, cabinets, and other devices penetrate completely through walls as this can be detrimental to sound isolation and fire resistance.
Gypsum board installations require careful planning: accurate measuring, cutting and fitting are very important. In residential buildings with ceiling heights under 8′1″, wallboard is best installed at right angles (perpendicular) to framing members as this orientation of the panels leaves fewer joints to finish. On long walls, horizontally attaching boards of the maximum practical length will minimize the number of butt joints. Avoid using damaged board.
Carefully measure where board ends and edges will meet corners and ceilings (Fig. 6). Accurate measuring reveals irregularities in framing and furring that require corrective allowances when cutting boards. Correct poorly aligned framing before attaching gypsum board (see Section II, Supporting Construction).
Fig. 6 – Measuring from Edge before Cutting Board
To cut gypsum board, working from the face side , first score the board by cutting through the paper to the core with a sharp knife (Fig. 7).
Fig. 7 – Using Utility Knife to Score Board
Then snap the board back and away from the scored cut on the face of the board(Fig 8).
Fig. 8 – Snapping Scored Board
Sever the board’s backing paper by snapping the board in the reverse direction or by cutting the backing paper with a scoring knife. Gypsum board may also be cut using a hand saw. Smooth all cut edges and ends of the gypsum board to form neat, tight-fitting joints when installed. Smooth ragged ends or broken edges with a rasp or sandpaper, or trim them with a sharp knife. If burrs on the cut ends are not removed, they will form visible ridges in the finished surface.
In light commercial and residential construction, single-ply gypsum board systems (Fig. 9) are the most commonly used wall and ceiling systems. Usually such systems meet fire resistance and sound control requirements2. Multi-ply systems (Fig. 10) have two or more layers of gypsum board that will typically increase sound isolation and fire resistive performance.Multi-ply systems also provide better surface quality because face layers are often laminated over base layers, so fewer fasteners are needed to attach the face layer. As a result, surface joints of the face layer are reinforced by the continuous base layers of gypsum board. Nail popping and joint ridging problems are less frequent, and imperfectly aligned supports have less effect on the finished
2See GA-600, Fire Resistance Design Manual, for specific details and description of fire rated and sound rated assemblies.
Fig. 9 – Single-Ply Application
Fig. 10 – Multi-Ply Application
Ensure satisfactory results with either single-ply or multi-ply assemblies by requiring proper:
·framing details (straight, correctly spaced, properly cured lumber)
·job conditions (controlled temperature and adequate ventilation during application)
·application of the board (measuring, cutting, aligning, fastening)
·joint and fastener treatment
·special requirements for proper sound isolation, fire resistance, thermal properties, or moisture resistance.
Ceilings exceeding 2500 sq. ft. in area, and partition-, wall-, and wall-furring runs exceeding 30 ft. all require control joints. Do not exceed 50 ft. between ceiling control joints in either direction. Install a control joint wherever ceiling framing or furring changes direction. Do not exceed 30 ft. between control joints in walls or wall furring. Be sure to install a control joint where an expansion joint occurs in the base of an exterior wall. Wall- or partition-height door frames may serve as control joints. Whenever possible, ensure that control joints coincide with any building control joints. NOTE: Where a control joint occurs in an acoustically rated assembly, provision may be necessary to block the sound at the joint opening by using backing material, such as gypsum board, mineral fiber or equivalent, or filling the void created with resilient insulating material.