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Would you like to add information to this article? Interested in writing or submitting an article? Have a question about this article? Mist systems and relative humidity by Professor Gene Wengert Q.
A.
So long as we are discussing humidity, three additional points: First, do not humidifiy your plant to a level that is wetter than the customer's home or office. Why? Because, if your plant is humid and the lumber is equally moist, you will solve all the cracking and warp problems in the plant, but you will just postpone these problems until the customer gets the product. It is better to have the problem show up in the plant than in use. Second, the real cure is to get dry lumber (maximum of 7.0% MC in the winter for most of the U.S.) and keep your plant around 6% EMC (30% relative humidity). And, always double check the MC yourself--don't rely on a value stated in the invoice. Measure the RH with an electronic sensor--not the brass office-style devices. Third, if the temperature varies in the plant, so will the RH and the EMC. For example, assume that the temperature and RH are 75F and 30%, respectively, which means 6% EMC. If there is a cold spot at 65F, the RH there will be 43% and the EMC will be 8%. If there is a hot spot at 85F, the RH will be 22% and the EMC 4.5%. (As a rule of thumb, a difference between the MC of lumber and the EMC of the air of more than 2% will begin to lead to problems.) Professor Gene Wengert is Extension Specialist in Wood Processing at the Department of Forestry, University of Wisconsin-Madison. Click on Wood Doctor Archives to peruse past answers. If you would like to obtain a copy of "The Wood Doctor's Rx", visit the Wood Education and Resource Center Web site for more information. Have you reviewed the related Knowledge Base areas below?
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