Ask an Expert

Ask an Expert

Forestry, wood processing & certification

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 trying to find someone who can carry out timber grading for us. We are wanting to mill our own timber for an extension and want to have it graded but trying to find someone who can do it, is proving difficult. Would be grateful for any assistance. We are north side of Brisbane.

We don't know of any graders in Queensland although it's likely that there are some qualified people around. Perhaps Timber Queensland can put you on the right track. Their phone number is (07) 3254 1989. Failing that, NSW State Forests provides a grading service and you can find out more via this link - One of their regional offices might be able to help, or they might be able to put you in touch with someone in your area.

Q. What sort of recovery could someone expect from their private forest when it comes to milling same? x amount of logs would expect about a yield y amount of sawn product?

There are several ways of estimating the recovery from a log, taking into account the natural taper, width of sawcut and wasteage. To calculate log volume you can refer to tables such as the ones given in various forestry manuals. For example a set of log volume tables can be found at this website However, log volume won't give an accurate indication of recovery of sawn timber. To get a rough idea of recovery you might find the Sawing and Stumpage Comparison Tool useful. This can be found on the Private Forestry website at

Q. I’ve recently done a development project for my employer and we had to remove a fairly large Turpentine tree. I managed to salvage the main barrel of the tree which is pretty straight and is approximately 4m long with a 0.8m diameter. I’ve dropped it off to a small local timber mill to have it cut into 5” square posts. However the sawmiller has come back to say that such long narrow lengths would likely bow and never remain straight and true. I would like to make some use of the timber somewhere architecturally in my residential renovations as posts or beams but maybe this is not feasible. What other ways could the timber be cut allowing me to use it where it could be appreciated architecturally? Thanks for your help

We feel that your 5" (125 mm) square posts should stay fairly straight if they are sawn away from the pith (centre of log) and the tree in question grew straight, not leaning. Bow is less likely in larger trees than small, rapidly-grown trees, and yours is quite a large diameter log. However, it's always hard to know how much growth stress there is in a log until it's sawn. Bow may occur at the time of sawing as result of stress relief due to the sawing operation, or it may occur during drying, due to differential shrinkage. What the sawmill says is correct, ie. if there is any bow it will show up more in a longer piece. A 4 m piece would have four times as much deviation for the same shape of curve as a 2 m piece. Maybe you could utilise the posts in shorter lengths, perhaps as verandah posts which wouldn't need to be 4 m long. Since it's a salvaged log there's not much to lose by having it sawn.

Q. I work at a timber supply yard in New Zealand. I was wondering what methods you know to stop timber from warping and shrinking when stored outside under direct sun? This is mainly for the lower grades of timber, boxing, posts, etc. Any information or resources about this would be much help.

We weren't sure whether the timber you refer to is kiln-dried or "green" at the time it's placed outdoors. It's really not a good idea to store unseasoned timber outside under direct sun - it will definitely shrink, and possibly warp and split as well. In fact unseasoned timber will shrink whether it's stored inside or outside, but warping and splitting are more likely if it is exposed to direct sun. Even kiln-dried timber is likely to undergo some further shrinkage under direct sun, depending on how hot the sun is and how long the timber is exposed. Whether it will warp or not depends on several factors. Material with spiral grain is likely to twist, while material sawn close to the pith may bow if the moisture content changes significantly. To some extent this can be prevented by keeping the timber tightly strapped so any tendency to warp is restrained, although stresses in the wood are likely to be released when the strapping is removed. Also if the timber is placed on bearers to keep it clear of the ground, the bearers should be no further apart than 600mm for framing timbers and 450mm for flooring, cladding and moulding timbers. But the best strategy would be to store the timber under cover. This subject is covered briefly in Appendix H of Australian Standard 1684-2010, "Residential Timber-Framed Construction".

Q. Do you know the difference between rough sawn timbers and DAR (Dressed All Round) timbers. Can you explain it for me?

Rough-sawn timber is timber straight from the sawmill, so it has a rough surface. Construction timber is sometimes supplied this way. Dressed All Round (DAR) timber, referred to in some States as Planed All Round (PAR), is timber that has been put through a planing machine to give it a smooth surface.

Q. I'm wanting to source some rough sawn durability class 1 or 2 decking direct from a mill in NSW. Do you guys have a list of mills and what hardwoods they saw? I have been looking in the yellow pages but it is difficult to work out which ones have what.

I'm afraid we don't have a list of sawmills and the hardwoods they produce. We can only suggest you try an organisation such as Forests NSW, which is part of the NSW Department of Primary Industries. Forests NSW's role is to sustainably manage more than 2 million hectares of native and planted forest, so they should have a rough idea where various species are processed. Forests NSW has a website at which will give you more information about their activities.

Q. Does EWPAA or GLTAA have an accredited laboratory in Surabaya, Indonesia who is able to certify our products while we process our Factory Certification under the GLTAA Certification?

The Engineered Wood Products Association of Australasia (EWPAA) is located in "Plywood House", 3 Dunlop Street, Newstead, QLD Australia. They can be contacted by fax on +617 3252 4769, or by email via this link The EWPAA carries out certification on behalf of a number of manufacturers of particleboard, MDF, plywood and LVL. Information about their testing capability is contained in a press release at

Q. Would you please be able to advise what is the best environmentally friendly wood I should use to build a pergola? I would ideally like to use hardwood, but it is heavy and difficult to work with, so maybe you can suggest the best sustainably treated pine?

If you prefer treated pine for your pergola it is all produced sustainably from plantations in Australia and New Zealand. Various treatments are used - for situations above ground, pre-primed pine is available, treated with a light organic solvent preservative (LOSP). For timber in the ground, or in contact with the ground, CCA and ACQ preservarives are used. These give the wood a greenish tinge because of the copper in the preservative solution. However, pine that is treated with CCA or ACQ can be painted like any other.

Q. How many yrs to grow grey box timber in south qld?

That's a pretty open question because it depends on site conditions and also whether you intend to manage the timber in a plantation with weed control, watering, etc. or whether you are going to let nature take its course. As a very general guide we would expect it to take 60 to 80 years to produce quality timber under managed conditions. You might be able to get more specific advice from someone who knows your area, eg. the Queensland Department of Primary Industries. They have a website at which will give you more information.

Q. I am building a 6m x 5m deck in Victoria and was considering Merbau however I have since discovered that it is destroying the orangutans habitat so certainly not using it now! Can you please advise me of another type of timber that is less harmful to the environment?

We assume merbau was to be used as decking rather than for the supporting structure. If so there are several Australian hardwoods that are suitable for decking, including ironbark, tallowwood, spotted gum, jarrah, etc. However, not all merbau is sourced from forests inhabited by orangutans and another way to approach it is to look for merbau produced under a certification scheme. Merbau is an excellent material for decking and if you write the words "merbau certification" in your browser you will find more information on the subject.


Did you know?

In 2008 seventy percent of known old-growth trees are in nature conservation reserves.