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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 am currently investigating a matter where a contract specification called up Balau or Yellow Balau as an external decking material. The builder has allegedly installed a product referred to as Resak. Can you please confirm the durability class of both timbers, suitability for an externally exposed decks, natural characteristics that may be displayed by both timbers when used in this situation and their expected average life expectancy.

Balau is durable and rated Class 1 outdoors above ground, according to Australian Standard 5604-2005, "Timber - Natural durability ratings". This would give it a probable life expectancy of greater than 40 years according to Table 1 of AS 5604.  Resak is not included in AS 5604 but has similar durability properties according to a reference in our library ("Characteristics, Properties and Uses of Timbers, vol 1, South-East Asia, Northern Australia and the Pacific", Inkata Press, 1982). Both balau and resak are actually comprised of several different but similar species which are grouped together for trade purposes, like many S-E Asian timbers. The balau group is harder and denser than resak, but both are described in the reference "100 Malaysian Timbers" as "very durable". Balau has an interlocked grain structure, whereas resak is generally only slightly interlocked, so balau may be a little more resistant to splitting if this is likely to occur.

Q. I am wondering if you can tell me the difference between American Oak and Vic Ash? I believe that they are both hardwoods but which is better or higher quality?

American oak (white oak and red oak) is a "true" oak, ie. Quercus species, whereas Victorian ash is produced by eucalypts. Consequently Victorian ash commonly has gum veins (depending on grade) whereas American oak does not. They are similar in density and durability. Victorian ash has higher stiffness properties, but American oak is slightly harder. So one is not necessarily better than the other. Quality depends on grading - there is good quality material and poor quality material in both groups.

Q. I have a large table and 8 chairs made of mango wood. So far, the table has been used for indoor use only. We are looking to build a deck and are considering using the table and chairs for outdoor use (under a covered deck, not entirely exposed to the elements). First up, is that a wise move given this type of wood, and if so, what is the best way to protect the wood from the outdoor elements? We'd prefer not to paint the wood if at all possible. We are Sydney based so you have an idea of climate.

Mango wood is not considered a durable timber when exposed to the weather on account of its relatively low resistance to wood rot. However, it will give good service on a covered deck, protected from the rain. Any coating will alter the colour of the wood slightly but for a natural look we suggest outdoor furniture oil, decking oil or similar.

Q. I am looking for a suitable wood to use for a toe rail on a boat. It would be left to weather without treatment. I was considering Merbau but now realise that it may stain the white hull. Another posibility is spotted gum. Do you have any suggestions for a non staining timber suitable for an exposed environment?

Merbau performs well in exposed locations but, as you say, is likely to stain the hull owing to its high tannin content. Spotted gum would be a better choice from this point of view. A data sheet published by Queensland's Department of Primary Industries states that spotted gum "has a lower tannin content than most other eucalypts, therefore staining of paintwork, brickwork etc. as a result of water running over unpainted timber surfaces, is unlikely to occur".

Q. I build snow skis, and have been using Bamboo, Paulownia, Birch and Vic Ash. I am interested in making skis from native Australian timbers, and was hoping you could point me towards a suitable one. Ideally, the timber would be very stiff longways, and strong crossways, when milled into skis shaped planks (around 8-10mm x 80-130mm x 1700-2000mm), and the lighter the better. I have had the most success with vertically laminated Bamboo so far, but it is a nightmare to mill, and I would rather something native. Any thoughts?

Presumably the Paulownia would be the core, with a stronger wood laminated top and bottom? We think you are on the right track with Vic ash. A CSIRO reference in our library outlines the following requirements for skis: "A hard, tough timber, reasonably flexible, resistant to wear. Special selection is essential to eliminate cross grain and brittle heart". Suggested species are mountain ash and alpine ash (ie. Vic ash), spotted gum and red tulip oak. Note the requirement to use straight-grained wood. Grain direction is indicated by any surface checks, which will always follow the grain, or by drawing a sharp-pointed tool along the plank.

Q. I want to make my wife a large chopping board. I want a soft white colour with a nice grain like american oak or american maple. Could you tell me what species you would recommend? I want to order the timber ASAP.

For butchers' blocks hard timbers are preferred, but for domestic chopping boards almost any timber can be used as long as it has been seasoned (dried). If you like the look of American white oak, then that would be a good choice. A back-sawn or flat-sawn piece will have more grain feature than a quarter-sawn piece. Softwoods such as pine can also be used, assuming the board will not be subject to heavy wear.

Q. I'm thinking of buying a blackwood outdoor setting, but am wondering how well it will survive the weather - and also how often it will need to be oiled.

There are two issues here, the durability or rot resistance of the timber, and the difficulty of keeping its natural colour. Tasmanian blackwood is not a particularly durable timber when fully exposed to the weather - it's rated Class 3 on a scale of 1 to 4, which means it has a probable life expectancy of 7 to 15 years. This might be all you expect, but there are more durable timbers. Under cover, of course, blackwood will last indefinitely. Regarding frequency of oiling, it depends on exposure but we would expect it to need oiling at least once a year and possibly more often.

Q. I'm looking to buy DAR Western Red Cedar for external use and want to know how to specify its appearance. Some timber companies mention that their timber is "Class 2" appearance, but what does this actually mean? Should I expect knots etc?

We are not familiar with the term Class 2 in relation to grade or appearance, and wondered if in fact it relates to durability. Western red cedar falls into Durability Class 2 when used outdoors above ground. Generally western red cedar for joinery is supplied free of significant knots, but this is something to discuss with your supplier.

Q. Thanks for the prompt reply. There is another intriguing question. We have sloanea woolsii – common name yellow carabeen – family Elaeocarpaceae and corymbia tessellaris – common name carbeen or Moreton Bay Ash – family Myrtaceae In various texts, there seems to be some confusion between the two names carbeen and carabeen. Any comment on the derivation.

Our previous answer referred to carabeen, but the similarity of the name to carbeen shows the potential confusion when relying on common names. The two species are quite different, carbeen producing a much denser wood. While information on carabeen is not so readily available, a comprehensive data sheet on carbeen is available via this link:

Q. Can you provide or direct me to a fact sheet of physical properties for Yellow Carabeen - sloanea woolsii.

There doesn't seem to be much published information about yellow carabeen on the net. However, two books in our library have brief data. "Forest Trees of Australia" gives the following: "Sapwood not always clearly differentiated but very susceptible to Lyctus attack; heartwood light yellow to yellow-brown, uniform texture, density about 600 kg/m³. The wood is fairly easy to work and is used for plywood, joinery, furniture and turnery". "Australian Timbers Vol. 1" published by the Queensland Department of Natural Resources states: "Green density 880 kg/m³, dry density 610 kg/m³; Strength Group unseasoned S4, seasoned SD4; Shrinkage from green 2.5% radial, 6% tangential; Durability Class 4; Seasoning - Care needed, with risk of sapstain and surface checking."


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%.