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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. I need somebody to identifying what timber species the timber windows are on a job up in Glen Innes NSW. Are you able to recommend somebody up in the New England area that could do this, or alternatively somebody I could post a sample of the timber to for them to identify. Your help is greaty appreciated.

A positive identification can be made by examining a sample microscopically. Each species has a distinctive cell structure and specialists in this field use such characteristics to identify different species. A noted expert is Dr. Jugo Ilic whose consultancy is called Know Your Wood. For details of fees and required sample size send an email to knowyourwood@gmail.com.

Q. I would like to start by saying your site is excellent and very useful. My situation is: I have built a new bathroom and have incorporated a steam room, I am planning to build a bench seat out of wood but I am unsure of which type of wood will hold up best in the high humidity and moisture? I am situated in Tasmania Thank you in advance for your help.

In a steam room, or sauna, woods to avoid are those that exude resin when exposed to heat (some pines, oregon, etc) and those that have a high tannin content which may wash out in contact with moisture (many eucalypts). Technically, the denser the wood the more likely it is to hold heat, although all woods are good insulators relative to other building materials. Dimensional stability is also important in response to changes in moisture content. Taking all that into account we suggest kiln-dried western red cedar is probably your best option. Cedar is non-resinous, low density and has little tendency to swell and shrink with changes in moisture content. It does have a relatively high tannin content but not usually enough to be a problem in a sauna.

Q. We are looking for the best timber to specify for architectural timber trusses exposed . Member Size to be approx 200 x 70 for a solid looking truss. Length O/A is approx 6500mm I have been told Oregon would be green and would crack . Can you offer any advise on a suitable seasoned hardwood to specify that's available in the size required.

It's unlikely that any timber of 200 x 70 will be available in a seasoned condition unless it is recycled or glue laminated ("glulam"). Glulam will give you a high quality appearance and can be specified in a range of different species. You will find some interesting examples if you write "glulam images" in your browser, and the Glue Laminated Timber Association of Australia's website is also worth a visit at www.gltaa.com. Oregon is likely to develop some seasoning checks as it dries and will give you a more rugged look than glulam. Splits and cracks can be minimised (but perhaps not completely eliminated) by specifying Free of Heart Centre, and again you will find more information by writing that in your browser. When large sections of oregon are used a fine-sawn surface is often specified, rather than a planed surface, since the latter shows up imperfections more clearly. However, it would be wise to obtain some samples to see what the supplier understands by the term "fine-sawn".

Q. Please advise is merbau suitable to be embedded in the soil and fresh water? How long it will last? Compare Merbau and IPE. Please advise me which one is better?

Merbau is rated Durability Class 3 when placed in ground contact. This means it has a probable life expectancy of 5 to 15 years. The reason for the rather wide ranging estimate is that the actual life-span of the timber depends on how damp the soil is and whether termites are present. In dry ground, or where the ground is only damp intermittently, one would expect it to reach or exceed the 15 year estimate. There are several slightly different Tabebuia species that are sometimes grouped under the name ipe. True ipe (botanical name Tabebuia ipe, known in South America as lapacho negro) is rated Durability Class 1 and is very hard and heavy. We would expect it to have a longer life than merbau, although we don't have a long history of its use in Australia.

Q. I am wanting to turn a baseball bat. They are commonly made from American Maple or American White Ash. What Australian timbers match or surpass the properties of the American timbers for strength and durability? Weight needs to be fairly similar. Clean straight grain is vital. Other suggestions I have found are Vic Ash, Silver Ash, Magnolia etc.

The traditional Australian timber for sporting goods is the Queensland species silver ash, since it combines impact strength with reasonably low weight. Some Australian hardwoods have the required shock resistance but are a bit heavy to swing. We feel you will be unlikely to obtain silver ash these days, so your suggestion of Vic ash (mountain ash/alpine ash) would be a reasonable alternative. Straightness of grain is vital, as you say, and any hairline cracks will quickly reveal grain direction.

Q. Could you please advise if jarrah would be better to use? Does this also bleed? I have looked at the spotted gum and do not like the colour variations. Masters are stocking ejarrah which is pre oiled. Appreciate your advice.

Jarrah does bleed tannin when exposed to rain, although slightly less than merbau. However, scrubbing with deck cleaner before installation, as recommended by paint manufacturers, should help to reduce this. Alternatively, softwoods such as preservative-treated radiata pine don't have a tannin problem.

Q. Can you tell me whether the treatment on blue pine is water soluble? I have a few metres of blue pine on a structure on my roof, which also collects our drinking water. I've just realised after the fact that this could be bad. We have 50k litres of water storage, so if it is the concentration would be low. Do you have any information on toxicity and concentration?

The treatment does not "fix" in the wood in the same way that CCA does, and with prolonged washing traces are likely to be removed. However, depending on how much wood is exposed to rain, the concentration in a 50,000 litre tank is likely to be almost undetectable. Nevertheless we are not qualified to give an authoritative opinion on this matter and would refer you to the various Material Safety Data Sheets available on the net. You might also wish to contact the Poisons Information Centre for further information. It's also important to realise that Blue Pine is not protected against wood rot - the treatment only provides protection against insect attack. If there is sufficient rain washing over the wood to leach out the insecticide then there would appear to be a risk of decay, since pine is not a rot-resistant species.

Q. l 'm looking for a hardwood as timber barriers on the roof for the International shooting center. The timber should be able to absorb bullets and exposure in the sun. Also, it should be durable and doesn't rupture for a long time. Is there any species of timber u can recommend? Thanks!

We weren't sure how high calibre the bullets are, or how high-powered the firearms are, but it seemed to us that softwood might be better than hardwood. Dry hardwoods could be inclined to split on impact. A big chunk of western red cedar, on the other hand, would absorb the bullets and also stand up to weather exposure. Perhaps it would be a good idea to conduct some tests with different woods, eg. cedar and treated pine at the softer end of the scale and a red gum sleeper at the harder end.

Q. Hello - does Vic Ash have a very high tannin content?

There is a rough correlation between tannin content and the colour of wood. Lighter coloured woods tend to have a lower tannin content than darker coloured woods, although this isn't always a reliable guide. For example, American white oak has quite a high tannin content. It's also a general observation that durable (ie. rot resistant) woods tend to have a higher tannin content than perishable woods. Since Vic. ash is both light coloured and non-durable the indication is that it is relatively low in tannin. This doesn't mean it has no tannin, just less than some other woods.

Q. I have just had bifold Rosewood Timber doors installed. One of the panels of wood has two dark black dye patches in the wood which penetrate through the wood. It is not the grain, looks like dye or mildew. Is this normal? Any advice on how to get the stain out as joinery won't replace the piece of wood. The doors are going to be vanished. My carpenter tried to sand it out. But it goes right through.

Rosewood varies considerably in colour and often has black veins, so the patches you mention could just be natural markings in the wood, particularly if they go right through the panels, as you say. You can get an idea of the variation in rosewood if you write "rosewood images" in your browser. A number of images are shown on the net, some of which have pronounced black markings.

WoodSolutions

Did you know?

Australia’s native forests, timber plantations and wood products are net absorbers of greenhouse gases, sequestering 56.5 million tonnes of carbon dioxide in 2005, reducing Australia’s total greenhouse gas emissions by nearly 10%.