Table

Distances between fasteners for cladding boards

Non-profiled weather

30 mm from base

board

Bevel siding

30 mm from base

Swedish rebate

45 mm from base

Corner rebate

25 mm from base.

Open joints

Boards <IOOmm: 1 in the centre,

Boards > 100mm: 2 pre-drilled

(with washers)

Top-mounted

1 in the centre

Channel siding

25 mm from edge

Mounting onto the supporting structure will usually rely on stainless steel fasteners and washers. Tannin from woods such as western red cedar and oak will accelerate the process of corrosion in galvanized steel, and the iron will cause unsightly streaks on the wood, particularly if untreated. In principle, aluminium fasteners are also suitable for lighter boards which are not subject to marked distortion, since the maximum permissible load is less than that of the steel equivalent. Stainless steel clips have recently been introduced (Figures 8.23, 8.24) which allow an invisible mounting of rebated elements and allow for considerable shrinkage.The size of the joint is determined by the clips. The use of these clips is particularly advantageous in the case of treated (painted or stained) wood, since it is then unnecessary to perforate the paint or varnish with the fasteners.

Finishing

The boards may be supplied in their sawn state (with a slightly uneven texture) or may have been planed.

8.23 Stainless steel clips for mounting boards.

Woods of Durability Grades I and 2 can be used with no further treatment.They will gradually lose colour due to the effect of ultraviolet light and rain. Careful detailing of the design is essential to ensure equal discolouration. Sections below the roof line or balconies are less exposed to the elements and will therefore weather less quickly. This may result in a distinct contrast between the weathered and unweathered

8.24 The application of the clips as shown in figure 8.23.

sections. Planed boards will discolour more evenly, but the planing process must be thorough to ensure no scuff marks or other irregularities, which will be particularly visible in use, especially if the boards are then painted.The adhesion of any finish to the boards will depend on the type of wood and whether they have been treated to enhance durability. A rough texture gives a better adhesion. Some wood treatments (based on oil) greatly reduce paint adhesion, sometimes to the extent that it is no longer possible to apply any form of liquid coating. Generally, substances soluble in water do not affect the paint-ability of the surface.

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