Section IV – Multi-Ply Application
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Multi-ply construction uses one or more layers of gypsum board applied over a base layer. The use of multiple layers of gypsum board results in improved surface finish, greater strength and higher fire resistance and sound classifications. The base layer can be a gypsum foil-backed board, regular gypsum board, or other gypsum base material.
The maximum support spacing for multi-ply systems depends mainly upon the base-ply thickness and placement. See Tables I and II for proper framing spacing for wood and metal framing or furring. Table V shows fastener spacing for the base ply attachment.
Base Ply Fastener Spacing for Two-Ply Gypsum Board Application
When attaching a multi-ply system with a laminated face ply over wood supports, fasten the base ply in the same manner as in single-ply construction. Double nailing the base layer is not necessary because the fasteners used to attach the second layer will produce a firmly fastened system. The base ply may be attached with long edges either perpendicular or parallel to framing members. End joints of the base layer may fall on or between framing members. Position face ply joints over framing, and offset face ply joints from base ply joints. If the base ply is foil backed board, apply the foil side against framing.
Orient the long edges of a base ply parallel with the framing members unless a referenced tested assembly specifies otherwise. At inside corners, mechanically fasten only the overlapping ends of the base ply boards and omit fasteners from the face ply. The floating corner treatment is better able to resist structural stresses (Fig. 31).
Fig. 31 – Floating Angle in Multi-Ply Systems
If staples are used to attach the base ply parallel to the framing, drive staples with the crowns perpendicular to the framing in the field of the board and parallel to the framing when next to the finished edges. Where edges fall over supports, orient staples parallel with the finished edges. If staples are used to attach the base ply perpendicular to the framing, drive staples with the crowns parallel to the framing in the field of the board and perpendicular to the framing when next to the unfinished edges. Where edges fall over supports, orient staples parallel with the finished edges and perpendicular to the framing. (Fig. 32)
Fig. 32 – Applications Showing Staple Orientation
Drive staple crowns so that staples bear tightly against the board without breaking the face paper.
When attaching base-ply gypsum board to metal framing or furring, use screws at least 3/8-inch longer than the thickness of the board. When using no adhesive between plies in a perpendicular application, fasten the base ply with a single screw at each stud or furring channel around the board edges and with one screw in the middle of the board at each stud or channel.
In parallel application with no adhesive between plies, fasten the base ply with screws 12 inches o.c. along the edges of the board and 24 inches o.c. in each stud in the field of the board.
When the base ply is to be attached either perpendicular or parallel to metal framing 16 inches o.c. and with adhesive between the plies, space screws 12 inches o.c. for ceilings and 16 inches o.c. for walls. Do not exceed maximum screw spacing of 24 inches o.c. on metal framing for both walls and ceilings.
Offset the joints in a face ply at least 12 inches from joints in the base ply or as defined by the applicable test report. Perpendicular application is more common, as it usually results in fewer joints. When the face ply is attached with mechanical fasteners and with no adhesive between plies, use the maximum spacing and minimum penetration recommended for screws in a single ply application. Find these spacings in Section II under “Screw Attachment.”
Typical adhesive methods for attaching the face ply to the base ply in multi-ply construction include sheet lamination, strip lamination, and spot lamination. For sheet lamination, cover the entire back of the face ply with laminating
adhesive using a notched spreader, box spreader, or other suitable tool (Fig. 33). Adjust size and spacing of the notches to suit the type of adhesive being used. For strip lamination, apply adhesive in ribbons with a special
spreader. Space the ribbons 16 inch to 24 inch o.c. (Fig. 34). For spot lamination, brush or daub spots of adhesive on in a regular pattern.
Attach gypsum board using moderate pressure and promptly remove any adhesive squeezed out at the joints. Strip and spot lamination provide better results than sheet lamination in sound rated partitions.
Fig. 33 – Notched Spreader Used to Apply Adhesive
Fig. 34 – Applying Adhesive in Vertical Strips
Hold the face ply firmly against the base ply with supplemental fasteners, shoring or bracing as necessary while the adhesive is setting to ensure satisfactory adhesive bond. For ceiling applications, apply mechanical fasteners in the field of each laminated face ply. On side walls, place fasteners at the perimeter of the board where they will be concealed by joint treatment or trim. Note that in fire-rated assemblies, the specific fastener spacing is given for the particular assembly tested and may not be related to whether or not adhesive is used between the plies. Fastener spacing details in fire-rated assemblies are available from the sponsor of the test and, in many cases, from the Gypsum Association. In sound-rated partitions where fire resistance is not a consideration, one may attach the face ply vertically over sound insulation board or backing board with permanent mechanical fasteners at the board ends only. In such applications, omit intermediate fasteners and temporarily brace gypsum board until the adhesive has developed sufficient bond strength.
Gypsum board can provide a new finish on existing walls and ceilings of wood, plaster, masonry or old gypsum board. If the existing surface is structurally sound and provides a sufficiently smooth and solid backing, one may directly apply a ¼-inch or thicker gypsum board layer with adhesives, nails or screws. Use nails long enough to penetrate into the framing 7/8-inch. When using power driven screws, be sure that the threaded portions of the screws penetrate the framing not less than 5/8-inch.
Use a combination of furring and shims to provide a suitable framework over existing surfaces that are too irregular to receive gypsum board directly. Use the same support spacings and installation methods, per gypsum board thickness, recommended in Section II for new construction.
Remove all surface trim for mechanical and electrical equipment such as switch plates, outlet covers, and ventilating grilles and save them for reinstallation. Reset electrical boxes to the correct depth prior to the installation of new gypsum board.