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Wood species & their properties

Like to know what wood to use building a pergola or framing a barn? How about the difference between tung oil and polyurethane as a floor finish? How to revive decking or deal with merbau stains? Or how to meet the building code or bushfire standards? Or ask about the environmental advantages of wood or forest certification?

Q. Curious if you have any information on American Black Locust. Robinia Pseudoacacia? In particular the flame spread and fire resistance of it.

Black locust is not a commercial timber in Australia and therefore has not been tested to Australian Standards. Even in the United States where it is used for purposes such as fence posts and railway sleepers, it is not used in structures. The authoritative Wood Handbook, published by the US Department of Agriculture, includes flame spread and burn-through rates for a number of timbers but black locust is not one of them. So we are sorry we can't help in this instance. All we can say is that on account of its density it is reportedly relatively difficult to ignite.

Q. I am considering building a Crib Wall from Radiata Pine clearwood 100x50.It is common practice in NZ. I have listed the information required by the relative Council before they will consider the Building Application. Tensile Strength Flexural Strength and Modulus Compressive Strength and Modulus Water Absorption% 23C 24hr.Incr ease in weight IZOD Impact Resistance Modulus of Elasticity (Mpa) Shear Strength

Some of the properties required by the local Council are determined by the "stress grade" which the producer allocates to the timber. This would either be a VSG grade (visual stress grade) or an MSG grade (machine stress grade). However, the grading system doesn't assess water absorption or impact resistance, both of which seem a little academic in the case of a crib wall. Also it is not clear whether the water absorption rate is to be assessed in relation to timber immersed in water or exposed to the weather. The latter would seem more realistic. Trials in New Zealand on radiata pine exposed to winter weather showed that after seven days' exposure the timber reached a moisture content of 27%, sufficient to sustain decay. Details can be found on the net at http://www.nzffa.org.nz/farm-forestry-model/resource-centre/tree-grower-articles/tree-grower-august-2007/responding-to-moisture-how-do-douglas-fir-and-radiata-compare/. It would thus be essential for crib walling to be preservative treated. Clearly when dry weather prevails the wood moisture content is lowered again. The Izod test measures the resistance of a material (wood, plastics, etc.) to impact. Its main application in wood science is to timber used for striking tools such as axe handles, hammer handles and so on. It is difficult to foresee a situation where impact resistance would be relevant to the construction of a crib wall unless a tree fell on it or a vehicle crashed into it, in which case the wall would presumably be destroyed.

Q. Just wanting to check the suitability of different timbers for use as posts in an outdoor gym - posts will be in ground and out of ground exposed outdoors to a harsh coastal environment. My recommendation to suppliers has been to provide Class 1 timber in treated pine. Do you think that Cypress or Accoya are suitable alternatives? And do these products require different treatment or seasoning?

Treated pine would certainly be a suitable choice, treated to H4 Hazard Level for in-ground protection, or H3 above-ground. Depending on the sizes you need, it may be possible to obtain treated pine that is seasoned (ie. redried after treatment). Regarding the alternatives, cypress pine is rated Class 2 in-ground, and Class 1 out of ground. However, these durability ratings only apply to the heartwood, so cypress pine would need to be supplied sapwood-free. Since it comes from a fairly small tree this is sometimes hard to achieve but you could discuss this with suppliers. "Accoya" (a brand name rather than a type of timber) is acetylated wood, ie. wood treated by a process that modifies its properties and gives it a significant degree of decay resistance. Dimensional stability is also improved. Results from long-term field trials are sparse, but one 18-year field trial showed that the decay resistance of acetylated wood was about the same as CCA-treated wood. If suppliers of Accoya are prepared to give the same warranties as suppliers of CCA and ACQ treated wood, we feel it would be a suitable alternative.

Q. I am researching making wood arrows from australian timbers, and I am looking for woods similar to sitka spruce and oregon and port orford cedar. I am new to australian timbers, but im sure there is an australian timber that could be used successfully. The traits needed are reasonably tight growth rings, and straight grain, as they would be made through a dowel cutting machine.

A reference in our library ("The Commercial Timbers of Australia: Their Properties and Uses") suggests silver quandong, hoop pine and bunya pine for making arrows. Of these, hoop pine is now the most readily available, although there are limited supplies of silver quandong. For example, Cedar Works has some - their website is http://www.cedarworks.com.au/contact.html. Bunya pine may be available from boutique suppliers if you search the net.

Q. I'm building a sauna and looking for suitable timber for benches, walls and ceilings. Timber for benches should be dark (brown or red) even color softwood, I would not like to use WRC as the color varies a lot between the planks. Timber should not bleed, leach or leave any stains when it is getting warmer. Redwood looks really nice but no-one seems to sell it based on your supplier data. I've also considered American black walnut and cambia even those are hardwood and might have issues with keeping higher temperature. I've discussed this topic with several suppliers but they do not have any suggestions and they are afraid of the topic even tho I explained that I understand that this is a risk that I'm willing to take and I will not be blaming them if something goes wrong. I will test the proposed timber in the oven before making final selection. I would appreciate if you would have any comments on this topic.

Californian redwood was a popular joinery timber in Australia in earlier times when it was known in the trade as "red pine". However, supplies are now limited and we are not aware of anyone with significant stocks, although you might find some through a recycling company. Failing that, we still consider western red cedar to be your best choice. Selecting the darker-coloured material would come close to matching redwood, although perhaps more brown than red. You don't mention where you are located. A company in South Australia that will select even-coloured cedar is Otto & Co. If you wish to follow this up, phone Ken Otto on (08) 8362 3522.

Q. What is the best way to strip the bark off a cedar tree that you will use as a interior support column in a house?

The bark will peel off much more easily if the log is cut during the growing season (spring/summer). During winter when the tree is dormant, the layer between the bark and the wood stiffens and the bark remains more firmly attached. So try to arrange for your tree to be felled in late spring.

Q. I would like to use a "green" tree trunk as an interior support column in a cabin I am about to build. Will it shrink if I don't kiln dry it or is it a must that it be kiln dry ? I'm thinking cedar, oak or hickory if it matters.

A "green" (ie. freshly cut) tree trunk will shrink as it dries out but the good news is that it won't shrink in its length, regardless of the species. It only shrinks in the direction of the growth rings ("tangential shrinkage") and towards the centre ("radial shrinkage"). This generally creates longitudinal splits, but as long as they don't bother you there's no problem using a green tree trunk. Splits will be less severe in the cedars since their shrinkage rate is lower than the hardwoods.

Q. I am struggling to find clear yellow cedar for boat building. I live in Latrobe (Near Devonport) Tasmania.

The only company we are aware of that stocks yellow cedar (also known as Alaskan cedar) is Ridgewood Timber in Adelaide, although there may be other stockists. For information about available sizes and prices contact Jon Eldridge at Ridgewood on (08) 8341 1822.

Q. I am actually in St Leonards, Sydney not St Leonards Tasmania. Can you please suggest who in Sydney can provide a report?

In NSW, State Forests no longer provide an inspection service, so please ignore previous answers posted on our website that refer to State Forests. However, their former inspectors have formed a private company and you can access their details via this link: http://www.timberinspection.com.au/. They should be able to confirm whether or not the table is made from blackwood.

Q. My mum recently bought a dining table which was labelled as Tasmanian blackwood, however, we suspect it is not Tasmanian blackwood. Would you think the shop would provide a refund based our own judgement backed-up by a source such as this pamphlet about Tasmanian Blackwood? http://www.tastimber.tas.gov.au/species/pdfs/blackwood.pdf. If not, do you have any advisers/experts that could inspect the table, give us a report and help us back our claim for a refund? If you could provide a quote for this service that would be much appreciated. (We live in St Leonards).

It's usually best to have an independent report from a timber expert in cases such as this. If you are in St. Leonards Tasmania you could seek help from the University of Tasmania. They provide technical advice through their website which you can log onto via this link: http://www.utas.edu.au/csaw/technical-advice-and-trouble-shooting.

WoodSolutions

Did you know?

Logs from plantations cannot produce the sawn hardwood timber produced from logs currently harvested from native forests.