Have you ever had a piece of Butternut that fuzzed or just wouldn't clean up, or a piece of Eastern White
Pine that looked more like Southern Yellow Pine with its bold grain pattern? Chances are these boards contained abnormal wood
called "Reaction Wood".
There are two types of reaction wood and they usually are produced from leaning trees or trees with
large extended limbs. In softwoods it is referred to as "compression wood" and in hardwoods as "tension wood". My trick for
remembering which one is which is to remember that "conifers" starts with the letter "C" so they have
Compression wood. It is
interesting that the compression wood forms on the lower side of the pith on a leaning tree (see picture on reverse side) whereas
tension wood of the hardwoods usually forms on the upper side of the pith.
Reaction wood is much denser than normal wood with the Specific Gravity 30% - 40% greater in
compression wood and 5% - 10% greater in tension wood. Longitudinal shrinkage is also greatly increased, 10 times more than
normal for compression wood and 5 times for tension wood. With this abnormal shrinkage you get warping, especially when lumber
is planed, ripped, or resawed.
Ever had a piece of wood either continually pinch the blade of a table saw or, just the opposite,
widely separate as it is being fed through? That's probably compression wood. A lot of your distortions in stud walls is caused
by compression wood; and, like White Pine, even grained woods appear as uneven grained.
Conversely, the uneven grained woods like Southern Yellow Pine have duller and more lifeless latewood
and its contrasting grain is evened out. It is harder to drive a nail in compression wood, there is a greater chance of it
splitting, and compression wood may take a stain differently than normal wood.
Tension wood is harder to detect. Sometimes there may be contrasting colors such as the silvery
appearance in Sugar Maple and Aspen, or the light, whitish streaks in Butternut, or the darker color of tension wood in Mahogany.
The tough tension wood fibers are hard to cut cleanly and thus the fuzzy appearance. Even when the wood appears smooth after
sanding, there still will be microscopic fuzziness, which will result in stain being absorbed irregularly, which results in a