Ceiling and Wall lining

Frame Straightness

Variations in the straightness of the frame will be reflected in the wall and ceiling cladding. Frames should be checked for alignment before cladding commences and adjusted if necessary.

Frame Movement

Shrinkage of the timber frame may result in cracking of the cornices, particularly at mitre joints. To avoid this problem, the cornice should be fixed with a flexible adhesive. The use of high-build acrylic paints will help to mask any cracks.

Fixing to Masonry Walls

A concrete blockwork substrate may shrink and cause delamination if the plasterboard is fixed while the blocks are wet. All new masonry walls should be allowed to cure and dry for at least fourteen days before plasterboard is installed. To ensure adequate ventilation of the cavity between the substrate and plasterboard, a gap of approximately 12mm should be provided at the top and bottom of the plasterboard.

Control Joints in Substrate

Where control joints are incorporated in the substrate, there is a possibility of cracking of the plasterboard. This can be avoided by providing corresponding joints in the plasterboard.

Fixing To Plasterboard Walls

Plasterboard does not have sufficient strength to withstand the loads imposed by items fixed to or hanging from it. All fixings should be securely set in the substrate, ie the timber or metal studs or the masonry wall as applicable.

Enhanced Fire or Acoustic Performance

When enhanced fire or acoustic performance is required, this may be provided by a combination of plasterboard and stud framing or battens on masonry substrate, which has been tested for fire and acoustics. The exact form of construction used in the tests must be reproduced in the building, including the provision of furring channels, resilient mounts or other fixings as appropriate.

Mortar Joints “Read” as Darker Areas through the Render.

Uneven moisture in the block/mortar substrate commonly cause this type of uneven colour in cement-based renders and cement-based paints are. This affects both the short-term colour showing through the render (moist render is darker than dry render) and the long term colour (cement containing unhydrated C4AF, due to uneven suction, is a darker colour fully hydrated cement). Normal concrete blockwork, consistent with commonly acceptable Australian construction practices, exhibits the following properties:

• Considerable variations of the density and chemical content of site-mixed mortars (a tolerance up to 20% on cement content is permitted by AS 3700)
• Difference in suction of block and mortar
• Different drying rates of walls with different exposures.

Therefore it is inevitable that the joints will “read” through render and that the degree to which the joints “read” will be quiet variable from wall to wall. In broad terms, the solutions to reduce colour variation include:

• Applying a cement based coating, which still “reads” the joints, but in a manner similar to the rest of the house. This will be difficult to achieve, since there will remain variations in the moisture content of the particular wall and differences from the moisture content of the rest of the house.
• Applying a coating that “hides” the variations. Whilst this can provide an attractive finish, it will be different from the rest of the house.