All Things Gypsum: Attachment of Gypsum Board
When compared to the application process for other construction materials, attaching a sheet of gypsum board is a reasonably simple task. After all, how difficult is it to find a stud and run a nail or a screw through the board? Better yet, how challenging is it to apply some building adhesive onto a stud and run a couple of fasteners through the board to hold it in place while the glue dries? It truly is that simple. However, there are several considerations that must be weighed before loading up the tool belt with drywall nails or screws and hanging some board.
The first thing to determine before attaching gypsum board is whether the system being constructed is fire and/or sound rated, rated for shear or bearing an imposed load. If so, a different set of rules applies than if the system is not rated or loaded. Rated systems have been constructed and tested under laboratory conditions and loaded systems have been tested or engineered. In such instances, each system must be meticulously assembled with special attention paid to the methods and products of attachment.
Consequently, any deviation from the listed design, including selection and placement of fasteners, could compromise the performance of an assembly. And if a diligent inspector happened to notice a deviation, the assembly could be "red flagged" and not pass inspection. For this reason, attaching gypsum board in a rated or loaded system must be done according to the instructions prescribed in the specific design used.
Fire- and sound-rated systemsDescriptions of many fire- and sound-rated systems can be found in the Gypsum Association's "GA-600, Fire Resistance Design Manual." The proper fasteners to use in each system are identified in the manual. Should additional information be required, a copy of the original test should be consulted.
If the system is not rated or loaded, there are plenty of other considerations to weigh before selecting the ideal combination of fastener type and fastener placement. For starters (there are more later on): Is the system a single-layer application or a multiple layer application? Is the framing wood or steel? Will adhesive be used along with the fastener(s) of choice? And what is the gypsum board material being installed?
To the last question, for the purposes of this discussion, we will address only the non-rated application of gypsum wallboard produced to ASTM C 1396, "Standard Specification for Gypsum Board." The application specifications for gypsum wallboard are contained in two primary standards: ASTM C 840, "Standard Specification for the Application and Finishing of Gypsum Board" and GA-216, "Application and Finishing of Gypsum Panel Products." These documents address fastener application issues for the majority of gypsum board and gypsum panel products; however, they do not address the application of some gypsum board materials, such as gypsum sheathing, gypsum lath and veneer board. The fastener requirements for those products are contained in separate standards.
Wood framing offers the most flexibility in the choice of fasteners and application methods: nails complying with ASTM C 514, "Standard Specification for Nails for Application of Gypsum Wallboard"; type S and W screws complying with ASTM C 1002, "Standard Specification for Steel Drill Screws for the Application of Gypsum Board"; and 16-gauge, flattened, galvanized, divergent-point wire staples with not less than 7/16-inch-wide crowns can all be used when attaching gypsum wallboard to wood framing. Gypsum wallboard can also be adhesively attached to wood framing using an adhesive that complies with ASTM C 557, "Standard Specification for Adhesives for Fastening Gypsum Board to Wood Framing."
In a single-layer application over wood framing, a combination of nails and screws or nails, screws, and adhesive may be used to attach gypsum wallboard. Nails must be of sufficient length to penetrate through the wallboard and into the wood framing no less than 7/8 inches and screws must be of sufficient length to penetrate at least 5/8 inches into the wood framing, having passed through the wallboard. Adhesive must be applied in a 3/8-inch diameter bead over framing where ends or edges of two boards do not meet. Two separate beads of adhesive are necessary on framing members where ends or edges of boards meet. The wallboard must be applied over the adhesive within its open or working time to ensure a proper attachment and adhesive should generally not be applied to top and bottom plates of a wood-frame wall.
Multiple layer applications over wood framing may also include the use of staples to attach all but the final layer. Staple legs must penetrate no less than 5/8 inches into the framing.
Attaching gypsum wallboard to steel framing may be done using the aforementioned screws and/or an adhesive specifically intended for the use when bonding wallboard to steel framing. When used, screws must be of a sufficient length to penetrate steel framing members not less than 3/8 inch.
Laminating multiple layers of gypsum wallboard allows attachment using a combination of staples, nails and/or screws along with an adhesive. The finish layer must not be attached using staples, and careful attention must be paid to ensure that the length of the fastener is appropriate for the combined thicknesses of the layers of wallboard. In addition to adhesive, joint compound meeting ASTM C 475, "Standard Specification for Joint Compound and Joint Tape for Finishing Gypsum Board," may be used to laminate layers of wallboard. Type G screws meeting ASTM C 1002 are to be used for securing the layers of laminated wallboard together while the adhesive dries.
Fastener placementDetermining the correct fastener spacing when attaching gypsum wallboard is the perhaps the most challenging part of the whole process. Once the preferred types of fasteners have been determined, several more criteria enter the picture: Is the surface to be covered a wall or a ceiling? Is the framing spaced at 16 or 24 inches on center? Will adhesive be used on the framing and/or between layers of wallboard? Each of these conditions impacts fastener placement and must be assessed prior to the beginning of wallboard application.
Wallboard should be installed to ceilings before it is installed on walls, so let's look at the variables of a ceiling application first. Framing for ceilings is typically spaced either on 16- or 24-inch centers, and that distance will often determine the thickness of the wallboard to be used. Whether the framing is on 16- or 24-inch centers, fastener spacing for ceilings is as follows: On single-layer wood-frame applications without supplemental adhesive, nails are spaced 7 inches apart; on multi-layer wood-frame applications, base layer nails are spaced 16 inches apart if the face layer is also nail applied, and 7 inches apart if the face layer is laminated to the preceding base layer.
On screw-attached single-layer wood- or steel-frame applications, fasteners are spaced 12 inches apart; on multi-layer applications, base layer screws are spaced 24 inches apart when the face layer is applied using fasteners and 12 inches apart when the face layer is laminated to the previous layer. On multi-layer wood-frame ceilings using staples to attach the base layers, base layer staples are spaced 16 inches apart when the face layer is attached using either screws or nails, and 7 inches apart when the face layer is adhesively applied.
Face layer fasteners in a multi-layer system are applied based on the requirements for a single-layer system. And the use of adhesive with a single-layer system may allow the distance between fasteners to be increased; ASTM C 840 or GA-216 should be consulted for fastener spacing parameters.
Requirements for attaching wallboard to wall framing are slightly more complicated. On single-layer wood-frame applications without adhesive, nails are spaced no more than 8 inches apart. For both wood- and steel-frame systems, screws are spaced 16 inches apart when the framing is on 16 inch centers and 12 inches apart when the framing is on 24 inch centers. On multi-layer wood-frame systems, nails and screws are spaced 24 inches apart when the face layer is fastener-applied. If the face layer is laminated to the previous layer, nails are spaced 8 inches apart; screws are spaced 16 inches apart if the framing is on 16-inch centers and 12 inches apart if the framing is on 24-inch centers. The same spacing is essentially used with a multi-layer steel-frame system; however, the orientation of the base layer wallboard to the studs can modify the fastening pattern. ASTM C 840 or GA-216 should be consulted for information.
As with a ceiling application, the face layer in a multi-layer system is applied based on the requirements for a single-layer system, and the use of adhesive can modify the spacing requirements.
Fasteners should be installed by starting in the middle of the wallboard and working outward so that the edges are attached last. Fasteners should be installed at least 3/8 inches from the edge of the board.
Gypsum board, like any construction material, must be properly installed to function as designed. While what has been presented herein may be somewhat weighty and difficult to memorize, the good news is that all of this information-and more-is easily accessed by consulting the text and tables contained in GA-216 and ASTM C 840. Consulting either document prior to beginning your next project might help you avoid headaches later on.
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