What causes breakage in walnut chairs?
July 14, 2015 | 9:00 am CDT
Q.  We are experiencing breakage in walnut cut-to-size chair legs. A "normal" piece of walnut bends a lot and takes a lot to break. When it does break, it ”shatters” with rough, splintery ends. What we are experiencing is that some parts that break far easier and the break is far cleaner somewhat like honeycomb in a bee hive looks and straight across. Can you advise any information as to what we have going on here?
A. Your description makes it easy to identify this wood as “brash wood.” There are basically three causes of this wood—two are natural within the tree and one is man-made.
The first cause is wood that is much lighter in weight than normal for the wood species. This light weight is caused by very slow growth in porous woods like oak, hackberry and ash. With slow growth, there are more pores with air space instead of solid wood. Light weight is also caused by the formation of tension wood (hardwoods) or compression wood (softwoods) within the tree. In hardwoods, tensioned wood leads to excessive fuzzing. In softwoods, compression wood is identified by color and wider than normal growth rings.


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Most employees will be able to notice this lightweight wood, color difference or excessive fuzzing, if they actually handle the wood. Of course, with more and more automation, it is getting harder to cull such pieces prior to manufacturing.
A second natural cause of brash wood is decay (or rot). Even the beginning stages of decay can substantially weaken the wood. Such decay can be visually detected. The most common decay, white rot, appears as white zones surrounded by black zone lines. Shiitake mushrooms are actually white rot fungi, so enjoy your steak and mushrooms; just do not use the tree that they are from.
Third, we can also have this effect if we squeeze the wood excessively. Normally, this would require a lot of extra force, such as from a large clamp that was tightened excessively. I have seen a few handles that were forced into a hammer head and the high force right at the head damaged the wood, making the wood break with a brash failure. I do not think that this would be an issue with most cabinets or furniture manufacturing.


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Gene Wengert

Gene Wengert, “The Wood Doctor” has been training people in efficient use of wood for 45 years. He is extension specialist emeritus at the University of Wisconsin-Madison.