Ceilings in garages are subjected to different environmental conditions to those in habitable rooms. The following conditions may occur:

• Wind loads can disrupt uncured adhesive and prevent an effective adhesive bond from ever forming.

• Door operation may induce vibration in ceiling framing, adversely affecting nailed joints and disrupting adhesive bond.

• Framing that changes direction in the garage may result in insufficient perimeter support for the plasterboard.

• Moisture and high humidity in the garage can result in poor joint performance.

The above issues can also result in the poor performance of any installed cornice. While the performance expectations for garage ceilings remain the same as for internal ceilings, additional details are required to ensure this performance is achieved.

Use the 1/3 spacing method of fixing plasterboard, as detailed in the Installation Manual. Use screws not nails to fix ceilings. Use trimmers across the sheet width for support (refer to FIG 1). Back-block all joints in garage ceilings. Use a good quality wallboard sealer and two coats of paint. In areas of high humidity, use Gyprock Wet Area Base Coat in the jointing system. Framing.

Materials

Gyprock plasterboard may be fixed to timber or metal framing and masonry materials that conform to standards specified by the appropriate government building authorities.

All timber framing shall be in accordance with AS1684 " Residential Timber Framed Construction or AS1720.1 " Timber Structures. Timber used as a substrate for Gyprock plasterboard shall be defined as being in one of the following categories:

Category A:

• Timber with a moisture content under 16% at the time of lining. Based on 90% of timber members being within the specified moisture content range with the remainder being within 2% of the specification. (Generally seasoned or kiln dried timbers would be in this category).

• Timber with a moisture content above 16%, but a tangential shrinkage below 8%. (Examples of these timbers would include, cypress pine, douglas fir (oregon), hoop pine, slash pine, radiata pine, western hemlock, jarrah, red narrow-leaved ironbark, rose/flooded gum and spotted gum. Category B

• Includes all timbers with a moisture content above 16% at the time of lining, and which have a tangential shrinkage above 8%. (Examples of these timbers would include, alpine ash, blackbutt, karri, mountain ash, messmate, river red gum, silvertop ash, Sydney blue gum and tallowwood. Tangential shrinkage at 12% moisture content is defined in AS1720.2.

Metal framing shall be in accordance with AS1397, AS1538 or AS3623, as applicable. Gyprock plasterboard may be fixed direct to structural metal ceiling framing not exceeding 1.2mm thickness.

Concrete, brick or masonry surfaces which comply with AS3700 can be sheeted with Gyprock plasterboard adhered directly to the wall with Gyprock MASONRY ADHESIVE. (Refer to the publication Gyprock Plasterboard Over Masonry Walls, NGYP525). Alternatively, these surfaces may have a furring system applied in accordance with AS1684, and fixed in accordance with the appropriate Gyprock system.

Preparation

The fixing of Gyprock plasterboard linings is deemed to be acceptance of the substrate.

Substrate members that are to support a joint shall have a minimum flat fixing face width of 35mm for nail fixing or 32mm for screw fixing, to enable adequate fixing of the plasterboard. All other substrate members are not to be less than 30mm width.

All substrate members are to be straight and suitable for the application of Gyprock plasterboard. The deviation in the alignment of the bearing surface(s) shall not exceed the tolerances given in Table 2, 3 or 4 when measured with a straight edge over a span of 1800mm along individual members or across adjacent members. NOTE: A minimum of 90% of all framing shall be in accordance with the appropriate tolerance specified. The remaining 10% (maximum) of framing shall be within +1mm of the allowable deviation.

Where the alignment of the fixing surface plane falls outside the appropriate tolerance, a suitable levelling system is to be used. Where the alignment of the bottom chords of roof members fall outside the appropriate specification, a metal furring channel system on sliding clip fixings can be used to enable the levelling of the ceiling support plane. Refer to the Gyprock Ceiling Systems Installation Guide, NGYP570 for detailed information.

Trimmers are to be provided in the part of the ceiling framing system where primary support members change direction within a room. All openings are to be framed.

Where battens are used, they are to be selected and applied in accordance with AS1684, and maximum spacings are to be in accordance with Rondo specifications.

Gyprock plasterboard may be fixed directly over existing linings if they are firm, sound and suitably straight for the Level of Finish chosen.

Fixing Systems

CSR Gyprock has developed a number of fixing systems designed to cater for most construction methods. Systems are available to fix plasterboard to steel, timber, masonry, and CSR Hebel AAC.

For detailed information on AAC and masonry fixing systems, refer to specific CSR Gyprock brochures. The fixing systems detailed here are suitable for all Levels of Finish using timber or steel framing in Australian Regions A and B up to and including wind category N4 as defined in AS4055. These systems are based on a differential pressure of 0.5kPa.

Generally the recommended fixing system is a combination of adhesive and permanent fasteners. The use of fastener only fixing systems should be restricted to applications where adhesive cannot be used, such as in fire rated installations, tiled wet areas and over existing linings or vapour barriers. Refer to appropriate CSR Gyprock brochures for additional information in these cases.

Adhesives

Gyprock Acrylic Stud Adhesive can be used (in conjunction with fasteners) to fix Gyprock plasterboard to timber or steel framing. It is coloured blue for easy identification, and can be used on both timber and steel in temperatures not less than 5C. It has a low toxicity, and does not represent a fire hazard when used in confined spaces. It is easily removed from tools and hands before the adhesive cures.

Contact surfaces must be free of oil, grease or other foreign materials before application. The adhesive is applied with a broad knife to form 25mm diameter by 15mm high walnuts. Available in 5.5kg and 1kg buckets.

WARNING

Stud adhesive MUST NOT be used on TILED WET AREA systems. Daubs of adhesive must never coincide with fastener points. Stud adhesive does not constitute a fixing system on its own and it must be used in conjunction with nail or screw fasteners.