No. 1 vs. No. 2 Common

Q. With the recent changes in lumber prices, we have been purchasing a lot of No.1 Common instead of No.2 Common. We are finding that our products seem to glue better and stay flatter. Can you possibly explain why this is so? Is it in the wood or in the way it is dried?

A. Based on my 50 years of experience in this industry, I believe that you are quite interested in yield. As a result, with the more knotty No.2 Common lumber, you are trimming the wood as close to the knots as possible. The wood around a knot that appears normal in color will actually be at a steep slope of grain. Some people might call this cross-grain. The wood in the proximity to a knot will actually glue like end grain instead of the more normal side grain. End grain and cross-grain are very difficult to glue successfully.

Further, cross-grain does warp a bit differently than the rest of the wood, so if the moisture changes, the regions with cross-grain will change shape or size differently.

It might be obvious at this point that when processing No.2 Common lumber, or any lumber with knots, is to make sure that the knot and any severe cross-grain associated with the knot is eliminated. The overall yield might drop a bit, but the yield of quality pieces will increase.


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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.