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We have newly-milled (from 100 year old beams) Tallowwood floorboards to be installed as our exterior upstairs verandah flooring, in our old terrace house. Whilst the verandah has a roof, the flooring is still subject to morning sun and some rain at the outer edges.

I know I have to weather the tannins out of the wood, to avoid them leaching onto newly painted brick and white iron lacework, before finishing them. My questions are:

- How do I weather the boards without them cupping (my carpenter's concern)?
- Can I wash/clean them to hasten the process?
- Do I wet both sides of the board and tongue/grooves of the board to avoid cupping? Do I do one side at a time and then turn and do the other when dried or just damp?
- How much can I safely wet them? Do I do it until dripping wet? Should I towel dry after hosing them down? (would this avoid uneven drying and cupping?)?
- Do I dry them flat or standing vertically (sorry if I'm using the wrong terminology)?
- Should I turn them regularly, or wet one side at once and then turn? (you can see the underside of the floor from the ground porch)
- My builder suggested laying them on the scaffolding we have where the air can flow under them also - is this a good idea or will it cause problems or uneven wetting/drying through the scaffolding holes?

I have no idea how to do this - with all the internet searches I've done applying to already laid decking, so a detailed process would be much appreciated. Then I have to figure out what to coat/oil them with!?
 

Woodsolutions Answer +

Tallowwood has a relatively high tannin content but is an excellent choice for outdoors. If possible, lay the flooring parallel to the external wall rather than by the usual method, which is at right-angles. Then it is only the outer boards that will be subject to weather exposure, rather than the ends of all the boards. Also it's important not to cramp the boards too tightly together so there is an allowance for a little expansion if they get wet. Regarding removal of tannin, we suggest you use one of the products described as 'tannin and oil remover' - you will find such products on the net. We don't endorse any particular brand since we haven't tested any, but we assume they perform as claimed by the manufacturers. Each product will have directions for use. We doubt the boards will cup from wetting during the cleaning process - tallowwood is quite a dense timber which only takes up moisture after prolonged wetting. Timber doesn't spontaneously release tannin, but only when water (eg rain) strikes a bare surface and washes the tannin out. So if you think rain will reach the underside it might be best to treat both sides of the boards.To dry the timber after treatment, stack it flat with spacer sticks between each layer so air can circulate through the stack. Avoid putting it in the sun while drying. Regarding a finish, we suggest decking oil once the timber has thoroughly dried.

Tannin removal

Answered on 13-04-2021
Please note that our answer is based on the best advice available at the time. If the National Construction Code, Australian Standards or local requirements have been subsequently amended, our answer may no longer be correct in all details. For more information, please read our disclaimer.

Question

We are building a deck 3m (wide) x 11m (long) & over 1m (high). What are the recommended post footings spans for the subframe, and the bearer and post sizes?

Woodsolutions Answer +

Our Technical Design Guide #21 titled Domestic Timber Deck Design provides a comprehensive guide to deck construction. It can be downloaded free of charge via this linki https://www.woodsolutions.com.au/publications. For timber sizes, the Guide refers to Australian Standard 1684. If you don't have access to AS 1684, timber sizes can be obtained from Timber Queensland's Technical Data Sheet 4 which is available via this link http://www.ozbuildmaterials.com.au/pdf/TQL%2004%20Residential%20Timber%20Decks0306.pdf.

Deck construction

Answered on 13-04-2021
Please note that our answer is based on the best advice available at the time. If the National Construction Code, Australian Standards or local requirements have been subsequently amended, our answer may no longer be correct in all details. For more information, please read our disclaimer.

Question

We have a large spotted Gum deck along the Western side of the house which was installed around 8 months ago. It has been left natural and allowed to grey off. It’s now at a point where we really like the look of the weathering and want to seal it so that it remains the same. What product would you recommend that we use to seal the timber. I don’t want it to change appearance from what it looks like now as I know some sealers with allow the timber to weather a bit more, while others give the timber that wet look.

Woodsolutions Answer +

We don't endorse any particular finishes since we don't have the resources to test them. However, it sounds as if Feat Watson's "Weathered Grey" might achieve the result you are looking for. Make sure you see it on a sample of timber before purchasing. You could, of course, just leave the decking the way it is if that's the look you want. Spotted gum stands up to the weather well without a finish, although applying a finish will help to avoid the fine surface cracks that occur in weathered wood. 

Weathered wood

Answered on 29-03-2021
Please note that our answer is based on the best advice available at the time. If the National Construction Code, Australian Standards or local requirements have been subsequently amended, our answer may no longer be correct in all details. For more information, please read our disclaimer.

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