Q: We are a furniture plant in the far North, where it is cold outside and dry inside. Last winter, like all the winters I can remember in the past, we had checking problems with our edge-glued panels. The ends seem to get cracks no matter what we do, although using a wax coating on the end seems to prevent most of the problems. When we remove the wax coating, however, we might see a few cracks develop. Can you give us any information?
A: Wood only changes its size or shape because its moisture content changes. When the moisture content drops, wood shrinks. When the moisture content rises, the wood swells. So, the cracks you can see are evidence that the wood has shrunk after gluing, which means a reduction in moisture content. So, we are 100 percent positive that the moisture of the wood panel pieces (some or all) is higher than the moisture of the air. (Although we could measure the air moisture with relative humidity, when dealing with wood we express the humidity in terms of the moisture content that wood will achieve in a given relative humidity air. At 30 percent RH, the wood will achieve 6 percent MC. So we say that air at 30 percent RH has 6 percent EMC.) So, the EMC of your plant's air is lower than the MC of the wood by at least 2 percent.
The wax on the ends acts as a nearly perfect buffer for the ends, preventing them from feeling the effects of the 6 percent EMC air on wetter lumber. But rather than use wax, which could potentially cause finishing problems, why not just try to get the MC and EMC equal? And the way to do this is to dry the lumber a little more. You could raise the plant EMC, but be careful. When the wet pieces get into the customer's home or office, they will dry out there, making any repair or adjustment very expensive.
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