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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. Is there a list or published book that compares English timber types with their equivalent in Australia please?

We don't know of a book that directly compares English timbers with Australian timbers, but the book "Wood in Australia" by K.R. Bootle is an excellent source of information on a wide range of species - not only Australian species, as the name might suggest, but all species commonly used in Australia, including imported timbers. We understand it is stocked by the Timber Development Association in Sydney - refer to this link:

Q. Can grey ironbark timber be steam bent for boatbuilding We are restoring a paddle steamer and find suitable spotted gum hard to get regards KEVIN

Back in 1948 when steam bending was more common, CSIRO published a leaflet which rated different timbers according to their suitability for bending. There were six categories, excellent, very good, good, fair, poor and bad. Spotted gum was considered "good", but southern blue gum (Eucalyptus globulus) was considered "very good". Grey ironbark doesn't seem to have been tested, but red ironbark was rated "bad". All timber for steam bending must, of course, be straight-grained. Grain direction can be checked by observing any surface cracks or splits, or by drawing a sharp pointed tool along the grain.

Q. is kwila as hard and strong as spotted gum if used on a semi trailer floor Thanks Doug

Spotted gum is significantly harder than kwila with a hardness rating of 11 for dry timber. Kwila varies from 7.2 to 8.6 depending on the source, so if resistance to abrasion is the main requirement, spotted gum would be the better choice. If loadbearing is the most important property there's not a lot of difference, although spotted gum is slightly stronger.

Q. What are the pros and cons of Hoop pine?

Hoop pine is an excellent general purpose timber, but whether it's pro or con depends what you want to use it for. On the plus side is the fact that it grows sustainably in plantations and produces very uniform, knot-free timber. On the negative side, it's rather bland-looking without a distinctive grain pattern, and needs preservative treatment if used in damp situations. However, hoop pine accepts treatment readily, whereas some species are difficult to treat. For more detailed information refer to the fact sheet published by the Department of Agriculture, Fisheries and Forestry (DAFF), available via this link:

Q. What durability class of untreated hardwood timber should be used in a school playground environment where:- 1/ The timber is partly buried in the ground. 2/ The timber is only exposed to the weather. Could you provide a list of timbers that would satisfy each exposure condition.

The answer depends partly on what life expectancy is required. Timbers of Class 1 durability in the ground have a probable life expectancy greater than 25 years. It might be the case that a Class 2 timber would suffice, with a probable life expectancy of 15 to 25 years. The word "probable" applies because site conditions vary. For example, if the timber is in damp ground, or a location where there is heavy lawn or garden watering, its life may be shortened. Hardwood species of Class 1 Durability in-ground include ironbark, tallowwood and some less common species such as woollybutt and white mahogany. Hardwood species of Class 2 Durability in-ground are more readily available and include spotted gum, river red gum, blackbutt, jarrah, etc. Timber out of ground contact is expected to last much longer. All the above species of Class 2 Durability in-ground (with the exception of jarrah) are rated Class 1 out of ground, with a probable life expectancy of greater than 40 years.

Q. What would be the best hardwood to use to make hiking sticks/trekking poles around 1450mm long and 25mm thick

The main characteristics required are resilience and straight grain. Of the readily available species, we suggest mountain ash or alpine ash (often sold commercially as mixed species under the name "Victorian ash"). Straight grain is essential to avoid unexpected fractures. Grain direction can be deceptive, since growth rings are not a good guide. If there are any hairline cracks in the wood, they will follow the grain. Otherwise, drawing a sharp pointed object along the length of the piece will show the grain direction, but of course will leave a scratch on the surface.

Q. Hi I live in Tasmania I am looking to select stair treads for my new house. The stringers are metal but I need a hard wearing wood, suitable for stair treads. Can you recommend a species please. regards jennifer

We recommend timbers with an above-ground Class 1 Durability rating for external stair treads. Hardwood species that fall into this category include spotted gum, ironbark, blackbutt, tallowwood etc. as well as imported species such as kwila/merbau. You should make sure the timber is kiln-dried, but some movement in service can still be expected. To allow for this, make sure the fixing method allows for slight swelling and shrinking across the grain as the moisture content of the wood changes. For example if the treads are screwed or bolted to the metal stringers with two fasteners, one of the fasteners should be in a slightly oversize hole.

Q. We are looking at using timber power poles in South Australia near Woomera. Would it be appropriate to call up a naturally termite resistant timber treated to H4 classification. Is there a species that is recommended that is available in South Australia?

Naturally termite-resistant timbers that are used for power poles are generally hardwoods. South Australia does not have major timber-producing hardwood forests, but hardwood poles could be brought in from other States. Alternatively, locally-grown radiata pine is used for power poles in parts of South Australia. Although not naturally termite-resistant, radiata pine can be readily preservative-treated to H4 level.

Q. I have 2 questions, 1. We would like to have exposed rafters in an area where there is active white ant infestations. Is there a timber that is easily worked & will resist white ants? 2. We are considering whether to use timber or aluminium windows but are close (about 1m) from the base of an escarpment. The air is damp & moist. Is there any literature which describes areas not suitable for timber? Thank you.

Regarding your exposed rafters, if you live in a tropical area such as north Queensland drywood termites can be a problem. Since they do not need contact with the soil, barrier systems are ineffective . In this case it might be worth considering preservative treated timber or a naturally termite resistant timber such as cypress pine. If you live outside the tropics, in one of the southern States of Australia, drywood termites are not a problem and it is only subterranean termites that are an issue. Barrier systems, installed at ground level, provide effective protection against subterranean termites and it is extremely unlikely they would reach your roof timbers if barriers are built in and regularly inspected. Regarding timber v aluminium windows, damp air will not usually raise the moisture content of timber to a level where decay can occur. A prolonged period of over 90% humidity would be needed, not taking into account the effect that a paint coating would have in retarding moisture uptake. Direct rain is the major factor in causing wood rot and we therefore recommend that timbers of recognised durability should be used for window joinery, coated with moisture-resistant finishes, if the windows are fully exposed to the weather. Suitable timbers include western red cedar, preservative-treated meranti, jarrah, merbau, etc.

Q. Hi, can you tell me if eucalyptus grandis is any good for jettys, mooring posts etc. in the river? thank you.

Eucalyptus grandis (commonly known as rose gum) is only rated Durability Class 3 in ground contact and if it's in salt water it has a low resistance to marine borers. It sounds as if it will be in fresh water, so marine borer attack wouldn't be an issue, but we would not expect a long life even in fresh water because of its lack of rot resistance. Durability Class 3 implies a probable service life that may be as short as 5 years in ground contact.


Did you know?

About 16% of Australia’s 147 million hectares of native forests are in nature conservation reserves.