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Specifying Wood

Initially, this sounds quite simple. You need a bit of wood for a job; so why not just ask the supplier for the correct size and the right number of pieces; and then that’s it, isn’t it?  Well…no!

“Timber” is not one, homogeneous “thing” which does anything you ask of it: just as the term “metal” doesn’t really help, when you want some of that stuff – Aluminium, Brass, Steel, Mercury: what job is it required to do, and for how long do you need it to do that?

Specification of timber requires an understanding of the properties of wood: things like strength, durability (resistance to rot), dimensional changes in response to moisture ( “movement”): and more subtle things, such as colour, texture, density, working properties (how easily can you machine it?) and so on. Not to mention other “customer” factors, such as those much-misunderstood terms “grade” and “quality”…so where to start?

A short article like this isn’t going to solve your problems in just a few lines, or a few minutes: but it can point you in the right direction; by making you realise that “wood” or “timber” are not universal terms that can be used to “specify” your way out of difficulty in a project (any more than a metallurgist would be able to define “metal” and its myriad uses in just 300 words!).

The vital thing to understand is that you must have a good idea of exactly what it is that you need the timber to do: and then you can (with help) find some options from the dozens (or hundreds!) of available species, that will have the right strength, adequate decay-resistance, appropriate moisture stability characteristics, correct working properties – and of course, appearance – that you require.

Which is why the world needs Wood Science!

Air-drying Hardwoods

 

Contributor:       Jim Coulson  CEnv FIMMM FFB AIWSc