Ask an Expert

Ask an Expert

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 seeking advice as to which timber (available in Australia) would be best to use for an indoor free standing (albeit sunken) hot bath with approx dimensions of 2500x2500 x 750mm. Things that worry me are Splintering, mould & rot resistance and fragrance. Could I have an expert's opinion?

We would suggest the boatbuilding timbers huon pine or King William pine from Tasmania. You will find lots of useful information on the net if you write "wooden bathtub" in your browser, but note that the sealer is just as important as choosing a suitable wood. Again, boatbuilding techniques will give the best results and we suggest using the epoxy saturation technique, or WEST system, which is explained in detail on this website: Amongst imported timbers western red cedar would be a suitable choice.

Q. I am thinking of installing driveway gates of timber. I have been advised that MERBAU is a good choice. The drive way is a full size and we would need the gates to close. Can you comment on the suitability of MERBAU GATES? Can you advise if the gates would need to be treated and if so how often?

Merbau performs well outdoors, but it has a high tannin content which causes a brown stain if the wood is exposed to rain. You ask if the gates would need to be treated. We weren't sure what you meant by "treated". Merbau is a durable timber which doesn't need preservative treatment. However, if left uncoated it will turn grey, like all timbers, and in the process the tannin will leach out which may cause staining of adjacent surfaces. If the gates are painted on all surfaces, preferably with an enamel (solvent-based) paint, tannin leaching will be prevented. If you intend to maintain a natural look by applying decking oil or a similar product it would be worth giving the gates a preliminary scrub with deck cleaner. Manufacturers of timber finishes recommend this as a means of removing excess tannin.

Q. My husband's business has a lot of western red cedar left over and I was thinking of making wooden plates to serve steak dinners with these pieces. I read somewhere that western red cedar can be toxic if ingested. As a steak knife would be used I was worried that little bits of wood might flake off. Do you think this would be a worry?

Some people have a reaction to western red cedar wood dust, particularly the fine dust produced by sanding it. That's possibly where you've read about cedar causing adverse health effects. It's actually not recommended to inhale any type of wood dust (or fine dust of any kind for that matter). Ingesting tiny pieces of wood is not likely to cause harm in the sense of a toxic reaction. Of more concern is the possibility of your guests getting splinters, or splinters becoming mixed up with the food, so using wooden plates in conjunction with steak knives is perhaps not the best idea.

Q. I am designing a structure on a beach, for use as outdoor fitness equipment. The equipment would utilise Timber posts. What would be the most appropriate timber to use considering: 1. The sea-side location 2. The amount of human hand contact 3. The fact that all posts would have exposed tops 4. Strength requirements

We suggest tallowwood which is a dense hardwood that won't absorb salt spray, is free from gum veins and has a slightly naturally greasy feel (hence the name tallowwood). It is therefore suitable for hand contact. It should also have the necessary strength requirements - perhaps you have had engineering advice on the required post size?

Q. I'm intending to use cypress macrocarpa for raised vegetable beds for clients of my business. I like it because it is sustainably harvest in my area, gippsland. My supplier says it will last 5 years in ground. But a few farmers have said that it won't last long at all. What do you know about the durability of macrocarpa?

We don't have a history of using Cupressus macrocarpa in Australia (common name golden cypress or Monterey cypress), but in New Zealand it is used for weatherboards where it is simply known as "Macrocarpa". The species is a native of California and the US Forest Service describes it as follows: "Monterey cypress wood is durable.  Natural durability of heartwood of Monterey cypress is high, 10 to 15 years' in-ground life and over 15 years above ground.  It is suitable for a wide range of exterior uses including joinery, shingles, and boats."  It is important to note that the comment about durability relates to heartwood only - the sapwood, or outer wood, is considered non-durable. It's also important to understand that timber which may be durable when harvested from a natural forest may not achieve the same durability when harvested from a plantation. Species planted in a climate different from their natural environment often grow faster and sometimes are less durable. In the case of a raised vegetable bed it will also depend on how heavily and how frequently the bed is watered. If you could devise some kind of liner that would keep moisture away from the inner surface, that would prolong its life, but even without that you should be assured of a five-year life span.

Q. I notice that Victorian Ash is not included in the recommended timbers for external window production. Fair enough, but do you have any idea why so many window fabricators are using it as standard?

Victorian ash is widely used for window joinery, no doubt because good quality material is readily available that machines well. One of the issues is that untreated Victorian ash is not considered a durable timber when fully exposed to the weather. It is rated Class 3 durability in above-ground external situations on a scale of 1 to 4, where 1 is highest and 4 is lowest. Of course, it makes excellent windows in a protected situation, such as under a verandah, and is capable of giving satisfactory service in weather-exposed situations if certain techniques are used. For example, some window manufacturers pre-treat their Victorian ash with a light organic solvent preservative (LOSP), applied as a pressure treatment. It has also been found that painting internal joints before assembling the windows, and then maintaining a paint coating thereafter, prolongs the life of ash windows, although sealing components before assembly is rarely done.

Q. I would like to use River Red Gum (Eucalyptus camaldulensis) for the internal doorframes of my house. It seems that people typically leave the wood unpainted when used internally. I plan to paint it white. Is this wood suitable for painting? Or is the grain quality such that a painted finish will look uneven and coarse?

Red gum will take a paint finish satisfactorily assuming it is seasoned material (kiln-dried or air-dried). Gum veins are common in red gum, but presumably you have selected your material to avoid this problem. Red gum that is free from checks, splits and gum veins actually produces quite a fine-grained surface, suitable for furniture. Have a look at this website:

Q. I am planning to build 3-4 russian saunas. Rough estimation is 11-12 cubic meters each sauna. I need either pine or larch logs 20sm diameter or beams. If you have other suggestion please do suggest. Also need your recommendation regarding suppliers, who is the best, to whom contact ?

If you are based in Australia it will be difficult to get larch logs and local pine is fast-grown, resinous, and not well suited to sauna building. Many sauna builders actually use planks although they often call them "logs". Interlocking boards or planks would be much easier to source, and in that case we would recommend western red cedar. This is readily available from Australian timber merchants. If you really want to use round logs, redwood from New Zealand would probably be the best material in our region. However, freshly cut logs have a high moisture content, which means there will be shrinkage as they dry out, and generally they taper towards the top which makes them hard to work with.

Q. Can you please confirm whether the ash from karri is black & jarrah lighter or visa versa. Have a builder wanting to recycle beams & I can't pick which they are.

This is known as the "burning splinter test" - karri burns to a white ash while jarrah gives a black char. Of course you need to know that the timber is either jarrah or karri and not something else altogether. Other timbers also burn to a white ash or a black char. You get the same result by burning larger bits. The only reason for using splinters is to get a quick result. Try to find a piece of fresh wood for the test, not a weathered piece.

Q. Do you know which Australian hardwoods have the lowest tannin content? I intend to use a hardwood for some outdoor seating and am concerned that the timber will stain the paving under.

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". Of course if the timber is painted, or sheltered from rain, tannin staining is unlikely since it's the action of the rain washing it out of the wood that causes the staining.


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%.