Dried wood or green? Back to Home Page
Experienced woodworkers will know for each project what sort of wood they will need with regards to how well dried or seasoned it is. This page is for those of us who are less experienced and would appreciate some help in this area.
If you read
woodworking magazines you might think that everything should be constructed
from kiln-dried timber, and it is certainly true that some woodworking
professionals use nothing else. But
there is actually a huge industry in
Advantages of green woodworking for traditional oak frame buildings
But isn’t it more sensible to plan ahead and use seasoned timber? Well actually the answer is a resounding NO! It is actually much, much easier to work the timber green, not only is it not so hard (oak becomes very hard indeed when thoroughly dried) but green timbers will be straight and so as the building takes shape everything will fit as it should. Over time the beams will dry and the characteristic bends and splits will appear but the integrity of the structure will remain. Also it would be very much more expensive to use seasoned timber and of course the sizes you need may simply not be available. If you are ordering the wood unseasoned the sawmill will cut to whatever size you need, even if it a rather unusual size. Yes we are perfectly happy to produce beams 5.5 inches by 8.5 inches if this is what you want – but there is no-one out there who already has fully seasoned beams of this size!
So having established that working with wood unseasoned is sometimes a big advantage for structural work like timber framed buildings let’s look at the other side of the coin. Furniture for indoor use is usually made from kiln-dried timber. Is this a good idea? Well the timber certainly has to be thoroughly dry for most furniture, but it doesn’t necessarily have to be kiln-dried. A lot depends on how thick the timber is and how long it has been drying; the design of the piece (can it cope with a little movement or would this ruin the item?) and as much as anything the species.
Oak likes to move!
Why is the species important? Well some woods move a lot as they dry. Oak is the best example of this – and for this reason it is not really a very sensible choice for furniture. It is used a lot because there is demand for it, but other woods such as Ash and Sweet Chestnut are far more stable and have equally beautiful grain. Many of the tropical hardwoods (such as Mahogany, Teak, Afromosia, Greenheart) are very stable and this is one of the main reasons they were used so much for furniture until the nineteen eighties. They are still highly suitable timber for such uses and many other uses but now it is recognised that sustainability has to be considered – they have also become very expensive as the indiscriminate logging is gradually stopped.
Another factor that is very important is the quality of the timber itself. Having said that oak moves a lot, if a high quality oak log is cut in the right way it can produce quite stable boards despite being Oak. A quarter-sawn board from a large, straight trunk with no large knots will be pretty stable, and will just shrink a little across the grain. On the other hand a plain sawn board cut right through a moderate size log including knots may be about as straight as a noodle by the time it is fully dried.
Other timber uses
OK, so what about the myriad of other uses of timber – how dry should the wood be? Well it does depend on a host of factors, not least the finish that is required, where it is to be used, the design and the width of each piece of wood (a wide board is very likely to cup or split as it dries, a narrow board probably will not).
Here are some examples.
We have supplied several bridge building projects with unseasoned Oak and Sweet Chestnut. The timber has to be high quality but not dry. This bridge at Cwmcarn Forest Drive (photo coming soon) built on behalf of Caerphilly County Borough Council by Marton Civil Engineering was entirely built in completely unseasoned local oak. Its timbers are now fully dried, but this took about three years after the bridge was completed and opened, and due to the inherent quality of the timbers selected it is proving entirely satisfactory. Previously Marton had used dried timber for another bridge (not supplied by us) and found the oak was moving so much the job became very difficult to complete. This bridge on the other hand, using green oak was built in winter, so no real drying out took place until spring when it was finished so construction was straightforward.
More examples and some photos will be detailed here as I have time….