An exterior grade hardboard (a compressed wood fibreboard) is manufactured in Australia to AS 2858, and is used as an exterior cladding.

It can be used in all exterior cladding applications. The manufacturer should be consulted for guidelines when using hardboard sheet cladding as structural bracing or, for construction details when diagonal or vertical application of the planks is being considered.

Hardboard exterior cladding is supplied in 3.6 metre long packs containing planks 9.5 mm thick and either 200 mm or 300 mm nominal width.

The long edges of the planks are lightly bevelled, and the face, edges and ends are factory prime coated.

Frames should comply with the requirements of the local building authority. Stud spacing should not exceed 600 mm. Before fixing hardboard cladding, all window sills, heads and other openings should be adequately flashed in accordance with good building practice.

The use of vapour permeable sarking such as fire retardant breather paper, is essential in walls subject to high wind conditions and wind updraughts. Sarking should be fixed on the outside of studs, and directly under the timber cladding.

When vapour barrier materials such as plastic film or reflective aluminium foil insulation are used, they are generally placed on the inside of stud frames directly under the interior lining sheets.

The use of sarking, vapour barriers and reflective foil insulation is discussed in more detail elsewhere in this datafile.

Job Preparation On-site storage prior to fixing should be under cover on timber gluts spaced at maximum 600 mm centres. If outside storage cannot be avoided the planks should be covered with waterproof materials to prevent staining.

Installation

Refer also to manufacturers data sheets for detailed explanation of fixing procedures.

Sheet hardboard is fixed in the same way as plywood cladding. The work sequence for fixing hardboard planks is generally similar to the fixing of solid timber boards.

Planks are nailed using 50 mm x 2.8 mm countersunk head hot dipped galvanised nails as recommended by the manufacturer.

When hardboard planks are used to cover existing cladding, galvanised flat head nails of sufficient length to penetrate and hold in the frame must be used.

Internal corners can be detailed using a timber stop, or the planks can be cut and scribed to match the splay of the plank on the adjacent wall.

External

Corners can be detailed using either a timber stop or a pre-formed metal corner available from the hardboard manufacturer. All exposed cut ends and timber stops must be primed with a good quality primer before installation.

Finishing and Maintenance Exterior hardboard cladding should be finish coated within 60 days of fixing. The factory applied primer sealer is compatible with most readily available paints.