Bamboo: timber or grass?
Ted Riddle considers the advantages and disadvantages of bamboo flooring.
I recently attended the HIA Sydney Home Show, and while it wasn’t as big as before, it did seem more targeted. With an insatiable appetite for discovering new and innovative products, the stands featuring timber and timber products generally caught my eye.
As per usual I picked my way around the flooring displays to see what new names manufacturers had pasted on rubberwood and other tropical hardwoods this year. One thing that never ceases to fascinate me is bamboo flooring.
I was standing in the display of ‘House of Bamboo’ when a voice behind me said, “they really make bamboo into nice timber flooring, don’t they.” As I turned around I recognised the voice as it belonged to a former colleague of mine from the NSW Timber Advisory service; he was obviously trying to get a rise out of me. We just laughed.
As we talked about all things bamboo we reminisced about another former colleague who always said ‘bamboo isn’t timber; it’s just grass’ and another of his favourite sayings ‘you burn wood, you build with timber’ both a couple of good old truisms, but I thought to myself, are they still true today.
Bamboo is of course a form of grass, albeit in some cases very big grass, but grass was the early development in the evolution of the flowering plant family that has become what we see as hardwoods today. Hardwoods are angiosperms, as are the bamboo species, the stems of which are both made up of woody fibre, therefore by definition: wood.
Subsequently I have searched for a definition of timber and although I am sure there is probably as many definitions as there are species of angiosperms, I think the four below reasonably qualify the question, and I found that many more were similar in their explanation:
trees that are grown so that the wood from them can be used for building;
wood used for building or making things;
wood, especially when regarded as a construction material;
that sort of wood which is proper for buildings or for tools, utensils, furniture, carriages, fences, ships, and the like.
The first definition considers ‘wood’ from trees, as to what constitutes timber, but the last definition, attributed as a legal definition obtained from ‘Websters’, more widely considers timber, so long as the ‘wood’ is proper for its use, and lists a number of options where the ‘wood’ from bamboo is often used.
I can hear a lot of old timber men turning in their graves when I make that reflection but it does seem a logical step to take when trying to figure out if bamboo is really timber… or not.
To use an analogy, if it looks like a duck, swims like a duck and quacks like a duck, it probably is a duck.
There are over a thousand species of bamboo, the largest of which is called giant timber bamboo, bambusa oldhamii, which naturally occurs in Taiwan and southern China and has now been grown extensively around the world as both an ornamental shrub as well as in plantations for wood production.
The giant timber bamboo can grow up to 20m tall with stem diameters reaching 100mm which is hardly saw log size. Most bamboo grows to optimum harvest size in 7-10 years; certainly a quick turnaround for harvestable wood fibre and wood products. Some species can grow as much as 91cm (3ft) in length a day.
Unlike timber from trees, where there are many different species used, individual bamboo species are measured to obtain the specific mechanical properties. While this is possible, it’s more likely that generalised properties are considered for bamboo because of the wide range of species, the similarity of appearance and the will, or need, to individualise the testing. Most testing results I have come across have derived from natural round material rather than as a wood product where it does give very good weight to strength ratios.
Generic understanding indicates that bamboo has very high compressive and tensile strength ratings when compared to other woods, brick, concrete and even steel. Other properties are hard to gauge though because of the wide range of species. In saying that, bamboo seems to compare well with most commonly used softwoods like Douglas fir (Oregon), Australian cypress and some of our ash type hardwood species.
With flooring being one of the main uses, particularly here in Australia, the Janka (or Hardness) rating is usually considered the main property referenced as it is used by the industry as the standard for determining the ability of a particular timber species to withstand denting and wear; the higher the number, the better the rating.
Conventional thinking rates bamboo at about 6 on the Janka rating scale with other common Australian flooring timbers such as Tasmanian oak/Victorian ash rating around 5 and Australian cypress 6-6.5, jarrah 8.5 and brush box 9. Many of the higher density species such as the ironbarks, grey gum, southern blue gum and spotted gum rate 11 and higher.
In Europe and North America it compares very favourably with such species as oak, both English and American, walnut, elm and beech all around the Janka 5-6 rating. Here in Australia, in the early 20th century, softwood species such as Baltic pine and kauri, both from New Zealand and Australia, were very popular and only rated 2-4 depending on the actual species.
I remember providing advice from the Advisory Service about the care needed when living with flooring species that had low Janka ratings. By understanding the softness and the possibility of impact damage it seems as though many of these species are regularly used and because of this I don’t see any problem with bamboo. I do know that many people do complain about dent marks in Bamboo, but then again they have probably never experienced or compared it to similar species commonly used outside of Australia.
One specific type/grade of bamboo flooring, referred to as ‘strand woven’ seems to have super Janka rating. I’ve seen it listed at 16-plus, which puts it up there with grey ironbark, grey box, turpentine and ebony.
From what I understand there is some conjecture over the testing with opponents saying they believe the Janka tests are being done at the node in the bamboo, where it’s definitely at its strongest, rather than on a random basis but I don’t think reputable testing agencies would enter into such deception as repeated testing would soon disprove the results.
As a natural product bamboo has many uses, as noted in our definition above. It can be used for tool components, utensils, fencing and widely used as scaffolding, particularly in Asia where the round tube weight to strength ration and flexibility give it some major advantages.
With many conventional timbers being used in similar ways to enhance the value, capability or resource recovery, the convention that timber only derives from the stem of a saw log capable tree and not from the actual manufacturing process, whether that be just longitudinal straight line cutting or some newer manufacturing process, that cuts, crushes, fiberizes, veneers, chips, grinds or glues, is the point to be considered.
To my mind, conventional lumber, as the Americans call it, cut from a round stem is probably timber. This means that some bamboo products could be genuinely called timber, while the rest are timber products; a reasonable compromise from an old timber man.