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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 replacing our currently carpeted stairs with solid timber stairs and the first builder has quoted on durian timber, polish grade. I originally suggested blackbutt but he dissuaded me from that based on cost. I had never heard of durian and have researched it, but am still not convinced that this is the best choice as not certain that it will be hard wearing enough. Is it? Should I insist on blackbutt or some other type of light colored timber (our furniture is Early American maple color)? This is a high traffic stairs and I am concerned about not only ensuring the wood is suitable but also that the polish finish will be hard wearing.

Like many tropical timbers "durian" is not a single species, but is the product of a number of similar but distinct species that are grouped together for commercial purposes. Consequently its properties are variable. The authoritative US Forest Products Laboratory quotes a Janka hardness rating for durian of 560 to 800 lb. This converts to 2.5 to 3.6 kN in the metric system, which is comparable to radiata pine. Blackbutt is considerably harder with a Janka hardness rating of 8.9 kN. That is not to say durian is unsuitable, depending on likely traffic on the stairs. If the stairs are only lightly used durian could give adequate service but it will have much less resistance to denting and would not stand up to high heeled shoes. Regarding a suitable finish, any flooring grade polyurethane would be suitable. However, a hardwearing finish will only increase resistance to abrasion and will not improve resistance to indentation.

Q. I had cypress pine tongue and groove in my house which has been changed to H3 treated laminated hoop pine. I have concerns hoop pine is softer than cypress and is not naturally termite resistant. I would like information on both materials taking into consideration I live in Chinchilla Qld. Also all of the rest of my house is cypress. Also I do not like chemical I prefer natural.

Cypress pine is quite hard for a softwood, comparable to the lighter hardwoods such as mountain ash and alpine ash. Hardness could be important for flooring and other surfaces that take heavy wear, but presumably is not an issue for the structural materials in your house. However, it is correct that hoop pine needs treatment to make it termite resistant whereas cypress pine has a natural resistance to termites without the need for treatment. From our point of view either material would do the job, but if you feel your specification has been changed without your approval that is a matter to take up with your builder.

Q. My husband & I are wanting to construct our house using our on-farm materials of mud/sand rendered strawbales and we have some murray pine logs for the main structure & frame work the flooring and ceiling. The logs have been logged from fallen dead trees the trees have been dead for a while however some we have logged still have moisture in them. We live in southern n.s.w around Deniliquin area in a temprature zone that is dry & hot around 45c in the summer & -2-3c in the winter our average rain fall is approx 11.5 inches/year. Any expert advice that you could give us concerning the milling/laying of the murray pine flooring and ceiling would be greatly appreciated.

Murray pine (also known as cypress pine) has a low shrinkage rate, but if the trees only recently died there will be some shrinkage as the moisture dries out. This is not likely to be important for the main structure, although some fine cracks or "checks" may appear. Shrinkage will be more of an issue in the flooring and ceiling lining so it would be wise to either use the drier logs for these products, or else saw the logs into boards and allow them to air dry before milling to their final profile. You are in a very low rainfall area which means that the level where wood moisture content reaches equilibrium will be low. Temperature is not important, it's the humidity of the air that governs the moisture content of wood.

Q. What is the density (Kg/m3) of Western Red Cedar?

Wood densities are average figures, since density varies from tree to tree and also according to the location within the tree. Consequently one finds slightly different figures quoted in technical references. An authoritative reference, "Wood in Australia" by K.R. Bootle, quotes a figure of about 350 kg/m³ for dry cedar, ie. at 12% moisture content. "World Timbers" by B.J. Rendle quotes 370 kg/m³.

Q. I have a job to supply some Blackwood for use in the chemical industy. Is blackwood the same as Blackbutt? This timber will be used inside a chemical storage tank and I believe they specify Blackwood as it will not contaminate the product.

Blackwood and blackbutt are quite different woods - blackwood was mainly sourced from Tasmania in the past and used as a decorative and furniture timber. However, it is correct that blackwood was also considered an excellent species for beer casks and tank staves. It is less readily available today but can still be sourced. You don't mention the type of chemical or the temperature at which the chemical will be stored. The effect of alkalis on wood is more severe than acids of the same concentration, and prolonged exposure to caustic solutions at high temperatures can have a drastic effect. Alternate exposure to acid and alkali is also particularly severe. No doubt the specifier has taken these considerations into account.

Q. We would like to select timbers to clad a beachhouse walls and have timber beams which we would like to grey naturally but not leach like blackbutt does, what timber species don't leach but will grey?

Since tannic acid is brown in colour, woods with a lot of yellow, red, or brown coloration to them tend to contain a lot of tannin. Using a hardwood with a light color, indicating a low tannin content, therefore helps to limit tannin staining. A hardwood that is unusually low in tannin is brush box, but since it is only rated Class 3 durability outdoors above ground, it's perhaps not the best choice for cladding that is to be left uncoated. Tallowood is moderately low in tannin, and spotted gum is considered a low tannin species although prone to gum veins. On balance, tallowwood is probably your best hardwood choice or, of course, cypress pine is free from tannin staining and has suitable durability.

Q. Over the years we have been working with rough sawn European Oak, Quercus spp., I am not sure of the exact species but from what I understand it is coming out of Eastern Europe. Normally when ripping or dressing boards of Oak it emits a very distinct vanilla smell, however there are some boards that emit a very strong smell similar to turpentine. On close inspection of the freshly dressed timber I have noticed damp areas with a liquid residue exuding from certain areas of the timber, these areas are oily to the touch and are the source of the odor. I know timbers, such as certain species of Pinus , are quite resinous, however I have never experienced this with Oak or any other timber. Are you aware of this occurring and is there any associated health or finishing problems with this timber.

We are not entirely sure of the cause of your problem, but we feel it could be a case of "bacterial wetwood". Typical symptoms are wet patches and a sour or rancid odour. It is more common in poplars and elms, but also occurs in oak, cherry and other hardwoods. The odour you describe as being similar to turpentine is likely to be acetic acid. You will find more information about this condition if you write "bacterial wetwood" in your browser.

Q. Could you please advise. A very pale cream timber with a grain pattern similar to oak, fairly dense but not too heavy, used for the packing of machinery from USA. I have been told that it is "Arctic Ash", of which I have never heard. Is there such a timber with this name or could you possibly suggest what it might be. PS I am a wood turner and have been given some of this timber for turning projects.

We are not aware of any wood with the common name "Arctic ash", although it is a name sometimes used in connection with imitation woodgrain products. We suggest the material you have is most probably one of the American white oak (Quercus) species or one of the American ash (Fraxinus) group. You can find images of these timbers on the net which might help you to make a comparison - just write "American ash image" in your browser.

Q. I am a beginner in wood carving and would like to find out please what type of wood is best for wood carving (carved signs or names on wood). I read somewhere that Basswood or Butternut are good for beginners but none of these seem to be available in Australia. Can you recommend one please and also where to get them.

Basswood also known as English lime (or linden in Germany),  is often recommended for carving because it is soft and even-grained. Low density hardwoods are best for beginners because hardwoods don't have such a significant difference between earlywood and latewood, ie. the light and dark alternating bands that comprise the growth rings in softwoods. However, as you have found, basswood is not readily available in Australia. A good alternative would be Paulownia which is grown in plantations in parts of Australia. If you don't have any luck with Paulownia, western red cedar would be good to start with. Although it's a softwood and has noticeable growth rings, it's easy to carve and is readily available from most timber merchants. If you are thinking of making carved signs for outdoors, cedar has good resistance to wood rot which Paulownia and basswood don't have, so that's an advantage.

Q. Thank you for your answer. I must correct my question, I did in fact mean Ironbark, not Ironwood. Does this in any way alter your answer?

That does alter our previous answer with respect to structural properties - spotted gum is considerably stronger than treated pine ("Ironwood") but similar to ironbark. More detailed information regarding Strength Groups and Joint Groups is contained in Australian Standard 1720, "Timber Structures, Part 1: Design Methods" (Table H2.3). However, our answer regarding warping and bowing remains the same - the critical factor is whether the timber is seasoned (dry) or unseasoned (green), rather than which species it is.


Did you know?

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