by Professor Gene Wengert
Q.
Have you ever heard of a wood called "Jarah"? Can you give me any information regarding it's characteristics (workability, durability) and suppliers?
A.
It is one of the species of Eucalyptus (from Australia). It is red, is extremely hard and dense (difficult to machine and glue compared to most North American species), has natural decay resistance, and is used for outdoor furniture sometimes.
There used to be a supplier in Milwaukee, WI. I'll see if I can find their name.
Professor Gene Wengert is Extension Specialist in Wood Processing at the Department of Forestry, University of Wisconsin-Madison.
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Comment from contributor A:
We who work on a regular basis with timbers in the Australian Outback *do not* class jarrah as hard. Hardness can be compared using the Janka test, which involves pressing a .444" diameter steel ball into the subject piece of wood until it is imbedded halfway in. In Australia the units used are Kilo-Newtons (I think the US uses ft/lbs and Europe uses Kilograms). Nevertheless, a comparison can be made.
In Australian terms, with red cedar it takes about 2.3 kN to imbed the steel ball halfway in, Oregan (Douglas Fir) 3kN, Teak 4.9kN, and jarrah takes 8.5kN. So jarrah compared to those species available in the US is quite hard. Timbers from Outback Australia, however, such as Brigalow (Acacia Harpophyllia), Mulga (Acacia Aneura), Gidgee (Acacia Cambadgei) and Coolibah (Eucalyptus Microtheca) along with others take 17 kiloNewtons to imbed the steel ball to half its depth(that is not a misprint - it is 17 kN). So by comparison, these timbers are 6 times harder than red cedar and Oregan, three and a half times harder than teak and twice as hard as jarrah. Incidentally, they are also extremely strong and very dense (they all have a density greater than 1). They work quite well with modern TCT tools, glue quite well with modern glues and have a beautiful figure (grain). They grow as small trees (typically < 8ft long and 10" dia logs), so therefore only come in small end sections (typically 1 x 2 up to 1 x 6) and up to 8ft long.
When green, it is relatively easy to work, but the older it is, the harder and more difficult it is to work. I am presently building a treehouse for my children from old jarrah. Each nail and screw hole has to be pre-drilled as it splits very easily and is so hard that a nail will often bend before going in half its length. Oiling finished jarrah will improve its appearance and durability. As an aside, I burn it in my stove and it burns very hot, down to large chunks of charcoal with virtually no ash. It is, however, a little difficult to start and needs to be cut relatively small as it is also resistant to fire. Green jarrah sinks like a stone when thrown into water and floats (just) when dry.
