The amount of shrinkage depends on whether there has been a period of time between milling and installation, or whether the weatherboards are being installed more or less straight from the tree without any drying. Worst case scenario is that jarrah can shrink by 6 to 7% of its dimension across the grain. Lengthwise shrinkage is negligible. Lapped weatherboards, installed horizontally, can deal with this level of shrinkage but you might also experience some cupping. If possible we would suggest some air drying in a protected location before you expose the timber to the weather, particularly as we are now in mid-summer. If you intend to paint the timber, a light colour will be less heat-absorbent than a dark colour and so the boards will be less likely to cup. If you have access to the National Construction Code (NCC) installation details are set out in vol. 2 pages 207-211.
WeatherboardsWe have a 1930's cottage in South West WA, that was built with rough, sawn jarrah as an external cladding for the building. We have renovated a rear 1980's extension and intend replacing the harditex cladding with green, rough-sawn jarrah weatherboards to clad the externals. There seems to not be much information online, so we are seeking as much information as possible regarding shrinkage, how to apply the boards, painting, curing etc. and really any other information that may be useful for undertaking this work.
Is Garapa Hardwood Decking available in Australia?
The South American hardwood garapa is available in New Zealand but we are not aware of anyone importing it into Australia. You might inquire from the New Zealand importer whether they are aware of any suppliers in Australia.
Garapa deckingI am having old timber decking on a front-door landing replaced due to weathering / deterioration. The landing is partially (but mostly) shaded from direct sun & rain. The original joists were installed in the early 1960s and upon removal of existing decking show no significant deterioration. But the originally laid (1960s) decking has been replaced at least twice over the years. When placing new painted hardwood decking, do you advocate the treatment of the top of the old joists before placing the new decking? Is this standard practice, as there does not appear any formal requirement to do so? Furthermore, is it necessary to paint/treat the undersides of the decking – particularly where they are nailed to the joists?
We do recommend treating the top surface of the old joists before installing new decking. Even though the joists may not show any sign of deterioration (perhaps they are a more durable species than the decking) it's an opportunity that won't arise again until you next have to replace the decking. However, we consider it less beneficial to treat the undersides of the decking. Presumably it's the top surface and the ends that have deteriorated due to exposure to rain. Suitable products for brush-on treatment of the joists include CN Timber Oil, Preschem Timber Preserver, etc.
Timber preservative
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