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 looking at using timber windows for a bushfire area (rating 12.5) and would like to know if hardwood and Vic Ash timber are other names for Silvertop Ash.

There are many types of hardwood. Victorian ash is comprised of mountain ash and alpine ash, two very similar hardwood timbers. Silvertop ash is a completely different species of hardwood. Bushfire Attack Level (BAL) 12.5 is rated low risk, where only ember attack is likely. Consequently, Australian Standard 3959-2009, "Construction of buildings in bushfire-prone areas" allows any type of timber to be used for window frames in BAL 12.5 if they are protected externally by steel, bronze or aluminium mesh insect screens (max aperture 2mm), or bushfire shutters. However, if the screens are wood-framed, the frame must be made from bushfire-resisting timber or from timber with a density not less than 650 kg/m³, otherwise metal-framed insect screens are OK. Also if the windows are less than 400 mm from the ground, or less than 400 mm above other flat surfaces such as external decks, the window frames have to be made from bushfire-resisting timber, or from timber with a density not less than 650 kg/m³, but in this case the glass also has to be Grade A 4mm safety glass.

Q. I purchased a desk and filing cabinet almost a year ago but have recently positioned them off the wall where the back faces the rest of the room and have noticed that the wood is different at the back to the rest of the desk/cabinet. I contacted the supplier and they checked their stock and said they are all the same. He suggested I contact a timber specialist and so here I am. Any advice would be greatly appreciated.

When the supplier says the desks are all the same we weren't sure whether than means they all have different timber on the back, or whether it's claimed that all the timber in the desk is the same, front and back. It wouldn't be unusual for a desk to have different timber (or a different grade of plywood) on the back since the back usually sits against a wall and isn't seen. However, if the supplier is claiming that all surfaces are made from the same timber, and you disagree, perhaps you need an expert to inspect the desk and give you a report. We might be able to suggest an inspector if you could tell us which State you are in.

Q. Our certifier has requested a test report from a registered testing authority to demonstrate that the Chestnut flooring installed is compliant with BCA clause C1.10 and Spec C1.10. I forwarded the data sheet from this website, however they won't accept flooring specs from a website. Do you have copies of test reports that were used to compile the data on your website? Your help would be greatly appreciated!

Australian "chestnut" is a marketing name for a group of very similar species, messmate, brownbarrel and silvertop ash. These have all been tested and found to fall into Material Group 3 with an average extinction area less than 250 m²/kg. We will send a copy of the test report direct to your email address.

Q. I am currently investigating suitable timbers for use in freshwater habitat improvement structures in Central Queensland. The structures will be a square stack of criss-crossed posts approximately 2m x 2m x 2m, designed to function as woody debris (snags). Most stacks will be fully submerged, some will be partly exposed. Desired characteristics: 25 year life span in freshwater Reasonable price Sourced locally (Central Queensland) Would rosewood (Acacia rhodoxylan) be suitable? I can get it locally at a good price and judging by the fence I put up at my property it's very dense. Not sure how it stands up to water though. Any information or suggestions would be greatly appreciated.

We don't have any direct experience of this timber since it's not harvested in significant commercial quantities. However, the Queensland Department of Forestry has a data sheet on Acacia rhodoxylan under the common name spear wattle. The data sheet gives it a Class 1 durability rating in-ground, and on this basis we feel it will achieve a 25-year life span in fresh water. The data sheet can be accessed via this link:

Q. I'm looking at building myself a Audio Rack to hold my substantially heavy audio gear. (I'm an amateur). I'm looking for a dark timber that has good sound absorption qualities. Any advice would be greatly appreciated.

It's important to make sure that whatever timber you use is kiln-dried so it stays stable. In the dark-coloured range, jarrah would be suitable. You might want to combine a solid jarrah frame with jarrah veneered particleboard if there are shelves in the unit. Make sure shelves have adequate support to avoid sagging if your gear is heavy.

Q. Hi What type of timber should I use for my ute tray?

Apologies for the delay in responding but our expert has been overseas. We suggest ironbark for your ute tray - it's a very hardwearing timber with good weather resistance. However, you should keep the tray covered when your ute is not in use, because if rain collects on the wood it will make it swell.

Q. I am an architect and am seeking a list of weight of various hardwoods per cubic metre (will vary with species and moisture). I cannot find this info on your site, but am sure it exists. Please advise.

This data is contained in various print media including the book "Wood in Australia" by K.R. Bootle, Australian Standard 1720 "Timber Structures, Part 2: Timber Properties", etc. A reasonably comprehensive list is available on the net if you paste this link into your browser:

Q. I am researching the Specific Gravity of Native Australian woods, i cannot find this information anywhere. Can you point me to the right site to obtain these figures.

This data is contained in various print media including the book "Wood in Australia" by K.R. Bootle, Australian Standard 1720 "Timber Structures, Part 2: Timber Properties", etc. A reasonably comprehensive list is available on the net if you paste this link into your browser:

Q. I’m hoping to get some advice on specification of timber that we’re using as exposed (non-structural) columns on a Retail Project here in Perth which is located approximately 50m from the ocean. We’re after a timber which is: 1. Mid-range in terms of cost. 2. Fairly dense and able to withstand a retail environment. 3. Able to withstand the proximity to the coast outlined above. 4. Able to be stained. 5. Available here in WA. If you could give suggestions (or ask for more information) it would be much appreciated.

Apologies for the delay in responding but our expert has been overseas. The timber species that comes to mind for your project is jarrah - a dense, hard-wearing timber, with good weather resistance and, of course, a local species. The seaside environment won't be a problem but metal fasteners will need to be highly corrosion-resistant, eg. stainless steel. The only difficulty will be maintaining the stain finish, assuming the timber is fully exposed to the weather. The denser the timber, the less the penetration of stain finishes, and consequently they tend to weather off hardwoods relatively quickly. We would guess that maintenance will be needed at least annually, although that will depend on exposure. Perhaps acrylic paint in a jarrah colour would serve the purpose with less frequent maintenance.

Q. Could you please advise best type of timber to use for fence posts. I would like to use river gum or forest gum ie 125 x 75. But cannot find it as such. Can you please advise alternative?

River red gum and forest red gum are good choices for fence posts, with forest red gum rated a little higher for in-ground durability. However, there are other options. You could consider treated pine, which is easy to work with, but if you prefer hardwood, blackbutt, spotted gum, ironbark and tallowwood are all suitable, with availability varying according to your locality.


Did you know?

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