Q. We just started processing some cherry lumber that was planed S2S by the supplier. We are seeing a small number of checks developing, especially in the flat sawn pieces. We are really perplexed as to what is causing this.
A. Dry wood is too strong to develop new cracks or checks. In fact, it is also difficult, but not impossible, to make any existing checks worse. Therefore, these are preexisting checks that show up when you expose the lumber to drier conditions than it has been used to. What happens is that the surface dries a little and with drying comes shrinkage, which opens existing checks.
I will bet that the S2S was done in a cool and likely more humid condition than the conditions in your shop. One might argue that your shop is too dry and that you should add humidity to your shop. However, if you raise your shop humidity, you will only be delaying the appearance of these checks until the customer gets the finished product and exposes it to low humidity in their home or office.
As most homes and offices are no drier than 30 percent RH (drier conditions cause printers and copy machines to work poorly with the dry paper, and humans get chapped lips, dry throats, etc.), try to keep your shop no drier than about 35 percent RH average for the day and night. Even if your shop is drier than 35 percent sometimes, which will make the checks open more, these are preexisting checks. Finding them now is better than finding them later.
Gene Wengert, “The Wood Doctor” has been training people in efficient use of wood for 35 years. He is extension specialist emeritus at the University of Wisconsin-Madison.
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