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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. Good afternoon, I have been asked to quote on 100mm thick hardwood that specifies a density of 40lb/ft3 (American spec.) I'm not 100% sure of this but I calculate that density to be around 640 kg/m3 ? Can you recommend a species that would meet the specs on that density?

That is correct, 40 lb/ft³ = 640 kg/m³. Many Australian hardwoods equal or exceed that density. We weren't sure whether the specs call up seasoned or unseasoned timber, since not all hardwoods are available kiln-dried in 100mm thickness. But virtually all commercially available Australian hardwoods have a density of more than 640 kg/m³ at 12% moisture content. The only exception we can find is alpine ash which falls slightly below at 620 kg/m³. To compare different hardwoods, visit the Wood Solutions website via this link:

Q. I am wondering if you were able to tell me whether merbau decking is poisonous at all. We have made an outdoor enclosure for our turtles and the wood has bled into the pond. I haven't put the tutles in the enclosure as yet as we have left the wood to bleed for the past 3 months. Is merbau treated before being sold? Or is the bleeding just natural? Just dont want to poison my turtles until i know its safe. The merbau is a feature wall of the enclosure.

Merbau decking is not normally treated with any preservatives as it is a naturally durable timber. The "bleeding" you refer to is the natural tannin content washing out of the wood. We have no expertise on the subject of turtles, but a quick search of the net suggests that tannin isn't harmful to them - for example, see the discussion on this site:

Q. I'm trying to build support for growing dragon fruit. It's a type of crawling cactus and likes to let its aerial roots grow into natural wood. Typically one would erect a post using any available cheap material eg galv. pipe, strong pop pipe etc and attach to it a natural untreated timber - even old tree trunk can be used. I would like to use rough sawn natural untreated timber approx. 1.8m high and 100 by 100 mm cross section but any other dim will do. Would you be able to help me with it? If not where about can I find such a material? Cedar woul be ideal as it resists moisture & water but I think oregon type timber would also be ok. Are you in Australia?

Yes, we are based in Australia but questions come from all over. We weren't sure whether the dragon fruit needs a soft timber for its roots to penetrate into, or whether hardwood is suitable. Oregon is not very durable outdoors as it doesn't have a high resistance to wood rot. A more durable timber such as red gum would perform better if it is going to be exposed to rain and/or watering of the plant. Other durable Australian hardwoods would also be suitable assuming the hardness of the wood is not a problem.

Q. I am sanding and refinishing a stair case where carpet had once been. Stair treads appeared to be all hardwood. Flooring contractor sanded and poly one coat and realized treads were oak on the left side where spindles installed but remaining stair tread was ash. Should a flooring expect have informed me that the stair treads were different woods and would not match. I have tried to get information on a builder used manufactured stair tread using both red oak and ash but have not been successful. Can you provide some information please.

It's sometimes hard to judge the appearance of different woods until a coat of sealer is applied. A coating is often said to "bring out" the natural colour of wood, usually darkening it to some extent. The technical explanation is that the air in the exposed cell cavities is replaced by a finish that has a higher index of refraction, in your case polyurethane. It might therefore be unreasonable to expect the contractor to notice that the woods were different until a coating was applied, since the grain pattern of oak and ash can be similar. Maybe the answer is to stain the wood before applying the poly coat to try to even out the colour.

Q. I practice karate and wanted to make a "makiwara" for use at home. It is a striking post for which I need a timber that is 1) strong 2) flexible and 3) suitable for outdoor use. If it helps, traditional woods used include "shijiya" (a member of the Japanese beech wood family), "hinoki" (Japanese cypress) and "sugi" (Japanese cedar).

Perhaps a rough guide to alternative woods would be density. Dense woods such as ironbark and other Australian hardwoods would be too hard and inflexible while low density woods may break on striking. Hinoki and sugi have an average density of around 400 kg/m³, although like all woods they vary. Radiata pine from New Zealand is in the right ballpark, often sold in Australia as "clear" pine on the basis that it is available knot-free. If your outdoor location is exposed to the weather, pine would need to be preservative treated, so perhaps material marketed for verandah posts would be suitable for your makiwara.

Q. I was just wondering if Tasmanian Oak would be suitable for making a pair of drumsticks It has a similar Janka rating to Japanese White Oak, which is what my favourite pair are made of and I was hoping to be able to replicate it.

Resistance to impact would probably be the most relevant property for drumsticks. It is usually tested either by the Izod test or by the falling hammer test. However, we have not been able to find any impact data for Japanese oak, so Janka hardness is perhaps the next best. Density is also a good guide. A reference in our library quotes 660 kg/m³ for Japanese oak, whereas mountain ash (one of the Tasmanian oak species) has an average density of 680 kg/m³, so the two are very similar. Just make sure your drumsticks are made from straight-grained material!

Q. Can you confirm that if the wall was a solid timber cladding/panel (ie. CLT style) 130mm thick we can only achieve an R-Value of 1.3 or does this value relate to a 130mm framed wall section?

It's often said that wood is a good insulator, and it is, but only relative to other building materials, most of which have lower R-values. For example a 90mm thick brick has an R-value of 0.14, so a solid brick wall 130mm thick would only have an R-value of 0.2. Compared with brickwork, wood is outstanding. However, insulation performance depends on the amount of trapped air in the material, so wood can't compete with products such as polystyrene, rockwool and fibreglass insulation batts.

Q. I would like help advising a customer on the R-Value of a Solid Wall manufactured using 130mm thick pine timber panels fitted between timber columns. The columns are the structural element.

According to CSIRO data, the R-value of pine is 0.01m².K/W per 1mm thickness. Therefore a 130mm thick wall would have an R-value of 1.3 without any additional insulation. This assumes there is no "leakage" through joints.

Q. I am after some timber to use for some sculptures I am working on, preferably a hardwood that will withstand the elements but will be easy enough to work with. I have some Australian Red Mahogany that I am using at the moment. I have oiled it to protect it, will it turn grey still? The pieces I am working on are around 50mm x 65mm in diameter and about 2 and a half metres tall. I have seen some fence posts that have turned grey and even have a slight orange tinge. Is this due to something growing on them? I am looking for that same natural grey finish but without too much cracking and splitting. Any wood you can recommend? I have a piece of Red IronBark in mind but I am thinking it might be a bit rough on my tools. Any help you can provide will be greatly appreciated!

To some extent there's a bit of a conflict between withstanding the elements and ease of workability, since it's generally the harder timbers that stand up best to the weather. However, your choice of red mahogany is a good one as it is a durable timber outdoors and is relatively easy to work. As long as you keep oiling it it won't turn grey, but that can be quite a chore as the oil doesn't penetrate deeply into the wood and so needs to be re-applied regularly. Regarding fence posts that have turned grey but have an orange tinge, we can only think that perhaps they are very old wood which is supporting some kind of fungal growth. This is unlikely to happen to your red mahogany, or at least not for a very long time. Whether it will crack and split depends on a number of factors, including whether the timber is dry or green, and if green, whether it is exposed to severe drying or a more gentle regime. Red mahogany usually dries with little degrade if the drying process is carefully controlled. Red ironbark is a denser timber that is very durable (ie. resistant to wood rot and insect attack) outdoors, but perhaps more inclined to hairline cracking during the drying process. Of course if you can find recycled ironbark, such as timber from old fence posts, it will already be dry.

Q. We are building a project home in Kellyville, Sydney. We want to know if Maple is a good timber for staircase. We have been told that maple is not hard enough. Is this correct. Cost wise, what is the best timber for stairs which is hard but not hard on the pocket.

Timber names can be confusing. The name "maple" covers a number of timbers - for example, meranti is sometimes called Pacific maple, or there's the completely different timber Queensland maple, or sugar maple from the US. If "maple" has been recommended for stairs it's quite likely to be meranti. This is not a particularly hard timber, but whether it will be hard enough for your situation depends on the wear it's likely to get. If everyone in the house wears flat shoes or sneakers it will probably be fine. If high heels are likely it will dent. We suggest you ask for clarification about the kind of maple that has been recommended and then decide whether you need a harder timber. Different timbers vary in price, but the cost of labour is a large component in a staircase, so timber that costs twice as much won't make the staircase cost twice as much.


Did you know?

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