Eastern hemlock (Tsuga Canadensis) is a magnificent tree that was abundant in our Eastern forest hundreds of years ago. Actually, there are 14 species of hemlock native to North America. Western hemlock, the most common, and mountain hemlock are the other two commercial lumber species; they grow primarily on the West Coast and are somewhat heavier and denser than Eastern hemlock. Although Eastern hemlock trees often exceed 100 feet in height with diameters in excess of 3 feet, a 988-year-old tree was 160 feet high and 7 feet in diameter.
North America native people and early European settlers used the leafy twigs of eastern hemlock to make tea (high vitamin C content). Tea from the inner bark was prescribed for colds, fevers, diarrhea, stomach troubles and scurvy.
The bark of Eastern hemlock is rich in tannin and was once one of the main commercial sources of tannins for the leather industry. At that time, trees were often stripped for their bark and then the wood was left to rot.
The wood of Eastern hemlock is quite knotty. Further, the wood is brittle (especially if dried under 10 percent MC) and splinters easily when nailed. Further, the trees are very susceptible to an anaerobic bacterial infection that enters through the roots and weakens the wood. In fact, any tree more than 100 years old (and many younger ones) will probably have bacterial shake (also called ring shake or wind shake), which is zone of separation of the annual rings. In addition to shake, the bacteria increase the wood's moisture content (heavier and higher drying cost), weaken the dry wood (splintering and shelling likely) and produce an unpleasant odor.
All things considered, today Eastern hemlock is not a highly desired species for high-quality lumber. Yet, if sawn from good logs and dried properly, it is indeed an excellent species. There are many instances where this inexpensive lumber can be used effectively and efficiently. Today, it is used for rough, general construction lumber (especially for non-load carrying applications), pallets, boxes, crates, railway ties and pulp. It is not used in large quantities for flooring, furniture or cabinets.
Processing suggestions and characteristics
Density. The density at 12 percent MC is 28 pounds per cubic foot. Dried, planed (3/4-inch thick) lumber will weigh just over 1-1/2 pounds per board foot.
Drying. Drying is difficult at times, with wet pockets being common. Wet pockets are small regions of very high MC within a dry piece of lumber. Brittleness due to over-drying is a problem. Most drying problems are related to resource problems, however.
Shrinkage during drying to 12 percent MC is 4 percent in the tangential direction (across the width in flatsawn lumber) and 2 percent in thickness. These are fairly low values.
Gluing and machining. Gluing is excellent. Machining is easy, except for the wood's brittleness, which results in splintering and cracking.
Stability. Hemlock is fairly stable, with a 4 percent MC change required to produce a 1 percent size change, maximum.
Strength. The mechanical properties are moderate. The strength (MOR) is 8900 psi, the bendability (MOE) is 1.2 million psi, and the hardness is 500 pounds. These are just a bit higher than for eastern white pine.
Color and grain. The sapwood and heartwood have the same pale brown color with a slight reddish hue. The wood grain appears coarse in texture. The annual growth rings are obvious.
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