Full Chisel Blog

July 28, 2009

The advantage of air dried wood

I suppose I should say the advantages, because there are several.  And this of course is in comparison to kiln or artificially dried wood.  During the nineteenth century and earlier all wood was air dried, the technology didn’t exist because it wasn’t needed.

Air dried wood was used when there was time for it to dry.  The standard is one year for every inch of thickness for hardwoods and a few months less for softwoods.  Of course this can change depending on temperature and humidity.  I have air dried one inch thick spruce and pine in less than 6 months.

Kiln dried wood was needed for the new balloon framing that became popular for house construction starting in the 1830’s.  Prior to that time the nature of the structures were such that it didn’t matter if the wood was dry and the builders took that into consideration when the buildings were built.

Most things were built with green wood, from log cabins, timber frames to legs and spindles on chairs, spinning wheels, there just wasn’t time nor a good reason to wait.  Green wood is much easier to work than dry wood, even air dried wood.  I have hewn green white oak and it works like dried pine, I would not attempt to hew dry oak, it would be possible but it would be a lot of work.

Working kiln dry wood makes shavings that are full of static electricity and stick to everything.  Green wood does not have the same static cling.  Air dried wood sometimes has static cling but not as much as artificially dried wood.  Air dried wood also works better, it stands up better under a chisel and tends to have more uniform firmness than wood that is speed dried.

When wood is heated above 185 degrees (F), fatty acids in the lignin change, harden and can not be altered from that more rigid state.  This produces wood that is harder and more brittle than wood that has dried naturally.  There can also be casehardening to the outside of the wood forming a refractory surface.  These can be a problem for working with tools, gluing with Hide Glue and can effect stains and finishes.

Wood when green contains both free water within the fibers of the cellulose and bound water which is within the cells themselves.  As the wood dries naturally (air dry) the bound water replaces the free water as it evaporates slowly from the wood.  As this happens the wood shrinks, more across or around the grain and not much at all in its length.  A board will get somewhat narrower but only its loss of length is insignificant.  When wood is artificially dried the water leaves quickly causing cell rupture and collapse.

The above illustration shows how wood seasons depending upon where it was cut from the tree.  Being aware of how wood seasons the craftsman would choose the proper cut of wood for the proper application.  Quarter sawn wood used for table tops and panels help maintain flat boards even if cut from unseasoned wood.

Today is is difficult to obtain air dried wood, almost everything is kiln dried.  In order to get the stuff, most times you have to dry it yourself.  It is indeed unfortunate that wood suppliers don’t offer an alternative to kiln dried woods.  When I get an opportunity to use air dried woods, I get a better idea of how woodwork was done in the nineteenth century and earlier.  The same applies to green (unseasoned) wood as its working characteristics are much different.

Stephen

2 Comments »

  1. Your post explains why I have stopped buying wood from one local source. I think they have turned up the heat and rushed things a bit much in the kiln. I make musical instruments and wood from this source had sometimes failed at glue joints under string tension. The fibers near the glue joint tore or broke away.

    I now choose to buy wood primarily from a local sawyer who offers wood both air-dried or run through a low temperature dehumidification kiln. I see little difference between the air-dried and kiln-dried wood I get from him. He also doesn’t steam wood so the walnut and cherry he offers has beautiful color.

    Comment by Doug Berch — July 28, 2009 @ 1:10 pm

  2. Thank you for the lesson. I am just starting to get into wood working and your post gives me a much better understanding than what I had.

    Comment by Dena at York Saw — August 10, 2009 @ 12:07 pm

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