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.
