CSR Gyprock recommends the use of curved trowels when setting recessed joints. Under normal pressure, a curved trowel deflects enabling the preparation of flatter and more consistent joints. A 200mm curved trowel is recommended for second coat application, while a 275mm curved trowel is recommended for the finish coat.

Tape Coat.

• Fill recess in plasterboard evenly and fully with compound using a 150mm broad knife.

• Bed in Gyprock PAPER TAPE centrally over the joint and cover lightly with compound.

• Cover all fastener heads and fill any surface damage with compound.

• Allow setting-type compounds (Gyprock BASE COAT) to set for at least one hour, and drying type compounds to harden for 24 hours. Second Coat.

• When the tape coat is dry, apply a second coat, about 180mm 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 to set for at least one hour, and drying type compounds to harden for 24 hours.

• When the second coat is dry, apply a thin finish coat of topping compound centrally over the previous coat, about 270mm wide. It may be useful to soften the outer edges of the newly trowelled compound with a damp water brush or sponge before feathering the edges 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. Sand smooth with 150 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.

Butt Joints.

Tape Coat.

Apply a thin layer of compound over the joint, (filling any recess created by back-blocking methods). Bed Gyprock PAPER TAPE and apply a thin coat of compound over the top of the tape compound must be spread approximately 150mm each side of the joint.

Second Coat.

When the tape coat is dry, apply a second coat of compound about 200mm wide to each side of the joint. This should have a gradual convex camber over the joint surface.

Finish Coat.

When the second coat is dry, apply a finish coat of topping compound centrally over the previous coat to form an even camber over the joint about 250mm each side of the joint.

Soften the outer edges of the compound with a damp water brush or sponge before feathering the edges with the trowel.

Sanding

. Allow the finish coat of compound to dry for at least 24 hours. Sand smooth with 150 grit paper or cloth, or with 220 grit sanding mesh.

Finished joints should have an even and slightly convex camber from edge-to-edge as shown.

Jointing Hand Applied.

Internal Corners

Apply a tape coat to both sides of the corner, and bed in the tape centrally over joint. When the tape coat is dry, apply a thin coat of finishing compound over the tape coat ensuring that the edges are well feathered.

When dry, sand smooth with 150 grit paper or cloth, or with 150/180/220 grit sanding mesh.

External Corners and Arch Beads.

Position external angle bead over the corner and sight it to ensure straightness before fastening both flanges at 300mm centres. External corners and arch beads are finished with a three coat compound system applied to the same specifications as for joints.

When compound is dry, sand smooth with 150 grit paper or cloth, or with 150/180/220 grit sanding mesh.

Decoration.

Interior Gyprock plasterboard surfaces may be decorated in any of a variety of finishes including flat, semi-gloss or gloss paint, wallpaper or vinyl, texture or stipple.

Roll coated paints generally have a greater coating thickness and create a similar texture on both the plasterboard and the jointing compounds.

No building material has an absolutely flat surface, and all that can be expected in practice is an appearance of flatness. The effect of glancing light on the appearance of flat surfaces is described in the CSIRO Division of Building Research Report No. L8 (Revised Edition). This report clearly demonstrates that surfaces that seem perfectly flat in diffuse light appear rough and uneven when light strikes nearly parallel to the surface.

Surface Preparation

All joint stopping must be sanded smooth. Remove all loose dirt and dust with a soft brush or dry cloth. Ensure that the joint treatment is thoroughly dry before applying sealer or paint.

Wallpaper and Vinyl

To enable removal of wallpaper and vinyl without damaging the plasterboard, seal the surface with a proprietary sealer.

Paint Finishes.

Select a proprietary paint system and apply all paints strictly in accordance with the respective manufacturers instructions. The use of a preparatory coat over the entire surface is recommended prior to application of the finish coats due to the differing texture and porosity of uncoated plasterboard and areas that have received joint treatment.

Recommended paint systems typically consist of one coat of a preparatory sealer followed by two coats of the finishing paint.

Preparatory Coat.

The chosen proprietary brand preparatory coat should be formulated to fulfil the following functions:

• Equalise variations in porosity over the entire surface.

• Provide a bonding surface or key for the finishing coats.

• Stop the migration or bleeding of chemicals from the substrate which could effect the performance of the finishing coat.

• Conceal the difference in texture between the paper surface and the joints.

• Plasterboard that has been fixed and allowed to stand for long periods prior to painting may become discoloured due to exposure to light. In this case the plasterboard surface should be sealed with a pigmented solvent-borne sealer before the application of finishing coats.

• In areas of high humidity such as bathrooms, kitchens, laundries and toilets, a paint system that protects the plasterboard and joints from moisture must be used. Refer to paint manufacturers recommendations.

• When applying the preparatory coat, apply a sufficient thickness to ensure that the surface is completely covered. Do not over-spread the paint.

• To avoid paint lifting over jointed areas, do not overwork or over roll the paint when applying the preparatory coat.

• Allow the preparatory coat to dry thoroughly. If necessary, lightly sand between coats of paint to remove any nap lift or other surface blemishes.

• In accordance with normal building practice, application of a finish is deemed to be acceptance of the substrate.

Always follow the manufacturers instructions for application and recoating. For best results, apply the coatings with a roller. This helps to achieve a full even coat and a light, uniform texture over the entire surface.

Refer to Australian Standard AS2311 The Painting of Buildings and/or paint manufacturers recommendations for specific roller nap length for the desired finish.