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've just had Wattyl Oil Modified Polyurethane applied to new Blackbutt flooring and it's bubbled (separated from the timber) in several places. Is this due to the "extractives" content mentioned for Blackbutt? In other words, does Blackbutt need special preparation in comparison to other flooring timbers to avoid rejection of such a finish?

We weren't sure if you have small bubbles in the finish, or larger areas where the polyurethane has separated from the wood. Small bubbles (or craters if the bubbles burst) can be caused by shaking the can, stirring or pouring roughly, or applying the finish with a furry roller, ie. actions which lead to air bubbles being trapped in the finish. If the coating is being rejected in larger patches it suggests that the surface might be contaminated. The "extractives" in blackbutt that can cause gluing problems are tannins, and the problem occurs particularly with phenolic resin adhesives. However, as far as we are aware tannins shouldn't interfere with the application of a coating. Blackbutt is not a particularly waxy wood. Perhaps Wattyl have had some experience with this problem and could advise you further.

Q. Can you please elaborate in relation to the use of cypress pine for jetty piles in lightly salted water, I intend to build a jetty in a lagoon not a river or creek. Would cypress still be ok?

The hazard associated with wood in salt water arises from the possibility of marine borer attack rather than the salt itself. A study by the Queensland Forest Service showed that some marine borers flourish in water of relatively low salinity while others require higher levels of salinity, so it would be wise to consider that marine borer attack is a possibility. Australian Standard 5604 rates cypress pine as a Class 2 timber with respect to marine borer resistance. This indicates a probable life expectancy of 41 to 60 years in southern waters, ie. from Perth in the west to Batemans Bay in the east, and does not apply to northern waters.

Q. I am looking at having some furniture made in Adelaide and the manufacturer told me New Zealand Pine is a lot better and harder than Australian Pine. Therefore, they only use NZ Pine. Is there a difference?

The density of pine (and therefore its hardness) varies according to where it grows, and according to genetic factors. New Zealand pine producers recognise three distinct density zones, with the highest density material produced in the north. However, it's not practical to specify which part of New Zealand you want your timber to come from. In general, Australian-produced pine is denser and harder than New Zealand pine, so your information is not quite right. Perhaps your supplier is referring to the fact that New Zealand produces much of the "clear" pine marketed in Australia. This is because they carry out high pruning to produce knot-free wood which is excellent for furniture and joinery.

Q. We are looking for a timber that has the same colour as well as same durability & strength as oak and that is readily available in Vic. Any ideas would be most welcome

An Australian-grown timber that is a similar colour to European oak, with comparable durability and strength properties, is tallowwood. It is typically a yellowish-brown colour, but like all woods it varies a little. We suggest you obtain a sample to make sure it satisfies your requirements. Tallowwood grows in New South Wales and Queensland but should be available to order in Victoria.

Q. I am looking for a readily available timber in Victoria that has the same properties as European Oak. I will be dealing with large chunks of wood ie sizes 150mm x 200mm for outdoor structural beams. The beams will be underneath a hut so will not be directly exposed to the elements. Somebody suggested Eucalyptus Obliqua but that doesn't sound very durable. Could you please advise?

Eucalyptus obliqua (common name messmate) is not as durable as European oak, as you say. A better match would be river red gum which has similar strength and durability properties to oak. However, such large sizes are unlikely to be available in a seasoned condition unless you can source recycled material. Therefore you should expect some shrinkage and "checks" (surface cracks) as the wood dries. However, green oak behaves in a similar manner, although its shrinkage rate is slightly lower.

Q. I have a builder putting in a deck and it has been raining for the last two days, he said it was Indonesian Hardwood and it has gone very weird. Almost like someone has put yellow streaks all over the wood, it looks like it is scratched into the wood? Can you tell me if this is dodgy wood or normal for this kind of wood, or even what type of wood this might be? When it dries it you can still see the yellowish markings but not as much. I think it looks awful and not what merbau should look like, but I am no wood expert.

The yellow deposits in the grain are a feature of merbau and actually an indication that you have the genuine article! In some countries the yellow is extracted for use as a dye. For more detail go to this website: The yellow deposits are water soluble and so the rain has obviously dissolved some of this material. With continued exposure to the weather the yellow should eventually wash out.

Q. What class durability is Oregon? I'd like to know what the difference between it and a Class 1 timber is, and whether a paint finish can improve its durability to Class 1.

Oregon is rated Durability Class 4 on a scale of 1 to 4 where Class 1 is the most durable and Class 4 the least. According to Australian Standard 5604, a Class 1 timber has a probable above-ground life expectancy of more than 40 years, whereas a Class 4 timber has a probable life expectancy of up to 7 years under "average environmental conditions". We wouldn't expect a paint finish to improve the durability of oregon to Class 1 status - a paint finish makes a difference if it's applied as a complete envelope, but in practice this is rare. The vulnerable areas in timber structures that are fully exposed to the weather are joints and housings, and even if timber is pre-painted all round it's impossible to maintain the areas that are concealed in joints or butted up against one another. On the other hand, oregon fascia boards that are kept well painted and not subject to water entry at mitre joints can last a very long time, so the specific circumstances can make a difference.

Q. We are using American Oak to timber floors and stair treads, and have specified brass nosing to stair treads. Can you suggest where we can access the Luminance factor of American Oak, in order to calculate the luminance contrast of the two materials, as required by AS1428.1 – 2009?

We assume you are providing for disabled access, since AS 1428.1 caters for people with disabilities rather than building work in general. So while AS 1428.1 calls for a minimum luminance contrast of 30% between the nosing and the background of treads on stairs that provide disabled access, our understanding is that it does not necessarily apply to all stairs in a building. Having said that I'm afraid we don't know of any testing to establish the luminance factor of American oak, or indeed any other timber.

Q. I am a wood turner and using crows ash to make a series of bowls and plates that food will contact. Is there any natural chemical that could be a problem health wise?

Crow's ash is inclined to have a greasy surface, but we are not aware of any natural elements in the wood that could be harmful. Presumably you will seal the wood before using the bowls and plates for food service. We suggest salad oil, olive oil, or other oils used in food preparation. If you intend to use the items frequently, regular oiling may be necessary.

Q. I am currently detailing a series of farm sheds out at Armidale and am wanting to know a suitable grade of timber to meet durability requirements for the timber joists, bearers and floor battens. The floors are covered by a roof but will be subject to animal urine and Faeces.

No doubt the floor will be hosed down from time to time, which also presents a hazard, although not too different from an outdoor deck exposed to the rain. We suggest a Class 1 Durability hardwood such as ironbark or tallowwood (or a combination of the two). All nails, bolts and other hardware will have to be a non-corrosive metal such as stainless steel or hot dip galv.


Did you know?

Australia’s 1.9 million hectares of timber plantations produce about two-thirds of the timber products consumed by Australians each year.