Hand Jointing of Recessed Joints & Back-blocked Butt Joints
Curved or straight trowels may be used for setting recessed and back-blocked butt joints. Under normal pressure, a curved trowel deflects and can assist in the preparation of flatter and more consistent joints. A 200mm trowel is recommended for second coat application, while a 250mm trowel is recommended for the finish coat.
• Fill recess with compound using a 150mm broadknife. • Bed in Gyprock Paper Tape centrally over the joint and cover lightly with compound. NOTE A minimum 1mm compound is to be left under the tape. • Cover all fastener heads and fill any surface damage with compound. • Allow setting-type compounds (Gyprock Base Coat) to set completely, and drying type compounds to harden for 24 hours before proceeding.
• Apply a second coat, about 170mm wide, finishing slightly above the board surface, and feather joint edges. • Cover fastener heads with a second coat of compound, laid in a different direction, and extending beyond the first coat by about 25mm. • Allow setting-type compounds (Gyprock Base Coat) to set completely, and drying type compounds to harden for 24 hours before proceeding.
• Apply a thin finish coat of topping compound centrally over the previous coat, about 250mm wide. Feather the edges of the compound with the trowel. • Cover previously stopped fastener heads with a third coat of compound, laid in a different direction, extending beyond the previous coat by about 25mm. Ensure that the edges of the compound are neatly feathered and that there are no trowel edge marks left in the final stopping. • Allow the finish coat of compound to dry for at least 24 hours before proceeding.
• Sand smooth with 180 grit paper or cloth, or with 220 grit sanding mesh. Avoid any heavy pressure which might scuff the linerboard.
Caution: If previous coats of drying type compounds are not thoroughly dry before application of subsequent coats, imperfections can result from delayed shrinkage of the compound.
Attribution: CSR Residential Installation Guide. The RED Book.
Levels of finish are defined in the Australian/New Zealand Standard AS/NZS2589. This standard is intended to provide builders, plasterboard installers and finishers, and their customers with the various defined methods and practices necessary to meet the customer’s expectations in terms of the ‘Level of Finish’. Three ‘Levels of Finish’ (3, 4 and 5) are defined, and minimum specifications to achieve each level of finish are detailed in the standard for each of the installation processes from framing preparation to finishing. All details may not be suitable for fire rated systems or multilayer systems. It is essential to determine the level of finish required before the frame construction begins, as specific tolerances are required for frame alignment as well as for plasterboard fixing and finishing for each of the levels of finish. Unless these requirements are met throughout construction, it may not be possible to attain the desired finish level without extensive corrective measures. The level of finish specified also affects the methods of jointing, particularly butt joints and back-blocking requirements, the number of coats of joint compound applied, and the fitting and finishing of stopping beads. Refer to TABLE 2. It should be noted that, generally, residential applications should be prepared to a minimum ‘Level 4 Finish’ unless specifically a higher or lower level of finish is agreed to by all contracting parties. Other commercial applications should be specified in contract documents. Selection of Level of Finish Factors affecting the level of finish include the surface’s visibility, the texture and gloss level of the final decoration and the lighting conditions. Critical or glancing light is that projected across the surface at low angles of incidence, as opposed to diffused lighting or light striking the surface at close to right angles. Refer to the following section “Surface Finishing & Lighting”. A good method to overcome differences in opinions of quality is to prepare a sample area in a suitable position and for all parties to agree on the finish. The following flow chart will assist in selecting the most appropriate Level of Finish for each area. For further information on levels of finish, refer to ‘Plasterboard Expectations’, available from the Association of Wall & Ceiling Industries.
For use in areas that do not require a finish, such as above ceilings and inside service shafts and other inaccessible spaces. All joints are to be taped with two applications of compound and all fastener heads are to be covered. Compound is to be finished smooth, such as by scraping ridges etc with a trowel.
This is generally the accepted level of finish for residential construction. Joints are to have a tape coat, and two separate coats are to be applied over the tape coat and fastener heads. All joint compound should be sanded to a smooth finish free of tool marks and ridges. Full details can be found in the Jointing section. Gyprock One Finish is a pre-mixed acrylic compound designed to create a uniform surface on interior walls and ceilings affected by critical lighting conditions. The application of One Finish over a standard level 4 finish will improve the final surface and minimise the effects of critical light, however it will not automatically upgrade the work to a level 5 finish.
This level of finish should be used wherever gloss or semi- gloss paints are to be used, where paint is mid or dark coloured, or where critical light conditions occur such as from windows, skylights, or silhouette and spot lighting. A three coat jointing system is required as for level four. All joint compound should be sanded to a smooth finish free of tool marks and ridges. This should be followed by the application of proprietary surface preparations by skim coating to remove differential surface textures and porosity. Skim coating is a term used to describe a thin finish coat, rolled, trowelled or airless sprayed and then possibly sanded, to achieve a smooth and even finish. It is normally less than 1mm in thickness and is applied over the entire surface to fill imperfections in the joint work, smooth the paper texture and provide a uniform surface for decorating.
Attribution: CSR Residential Installation Guide. The RED Book.
Movement and stresses created by temperature and humidity fluctuation, can result in deformation and damage to internal linings and partitions. It is recommended that Gyprock plasterboard surfaces be isolated from structural elements, by the use of control joints or other means where: • A plasterboard/wallboard surface abuts any structural element or dissimilar wall or ceiling assembly. • The framing or structural support changes within the wall or ceiling. • At all construction/control joints within the building. • For non-tiled internal walls with plasterboard outer layer, at 12m maximum centres. • For tiled internal walls, at 4.8m maximum centres. • For external ceilings, at 6m maximum centres. • At junctions with other building elements. • At changes of lining material. • At each storey or rise of studs. Control joints incorporated in a building to permit movement in the structure must be carried through all areas lined with plasterboard/wallboard. Allowance for movement must be made through the frame, lining and any tiles. Door frames extending from floor to ceiling constitute control joints. For doors less than ceiling height, a control joint extending from one corner of the frame may be used. Vertical control joints in stud framed walls are to be constructed using two studs with a 15-20mm gap between.
Attribution: CSR Residential Installation Guide. The RED Book