Understanding Reaction Wood
Have you ever ripped a thin strip off a board only to have it
immediately warp or twist? You might have also had the board pinch the
blade and cause friction burns or blade stalling. We often receive
e-mails from frustrated woodworker wondering why their "perfect
board" is acting like a sleepy two-year-old. These problems are
often caused by a difficult to detect condition in the wood called
"reaction wood".
In short, Reaction Wood is abnormal wood formed in a leaning tree.
In softwood trees, the reaction wood forms on the lower side of the
lean and is called compression
wood. Compression wood is often very
dense, hard, and brittle. In hardwood trees, reaction wood forms on
the upper side of the lean and is called tension
wood. Woolly surfaces
and excessive longitudinal shrinkage are often symptoms of tension
wood.
Reaction woods should be avoided for a number of reasons. The dense
hard wood is less likely to accept an even stain when compared to
other parts of your project. The reaction wood is also more prone to
failure under load and will crack and split more easily when nailed or
screwed. Carving and shaping can also be difficult and dimensional
changes with changing moisture levels are likely.
The primary problem comes in trying to identify reaction wood. Even
an experienced woodworker can have trouble picking out reaction wood.
There are some hints that a board may contain reaction wood.
Crookedness or a sweep in the log is a sign of reaction wood. Wood
fibers that are unusually dense and hard for the species is another
sign. Very small fuzzy fibers on surfaced hardwood can be a sign of
reaction wood as well as crack and splits that pull wildly away from
the board. If you find a piece of reaction wood
"accidentally", save it for future reference. Fortunately
reaction wood is more of an exception than a rule. And now, if you
happen to run across an uncooperative board, you'll have an answer for
why your cuts are twisting and curling.
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