Q: We have a small manufacturing operation near Pensacola, Florida. The air is really quite humid, so when the windows to the plant are open, the humidity inside is quite high too. When we ship our finished items, we find that we get a little warping and cracking in the drier conditions north of Atlanta. We do request kiln-dried lumber that is 6 to 8 percent MC. What else can we do?
A: I hope you realize that once lumber has been kiln-dried, it will lose or gain moisture in order to achieve equilibrium with its environment. In other words, kiln drying does not stop subsequent moisture movement.
Also, when I check the records, the climate in Pensacola is indeed very humid. Changing the relative humidity (RH) to equilibrium moisture content (EMC) tells us the moisture content that wood will be trying to achieve. I see that your EMC varies from 13 percent to 15 percent, on the average. This means that your manufacturing plant, with the windows open, will probably have an EMC of 12 percent to 13 percent - a little drier than outside. Wood in the plant will be trying to achieve 12 to 13 percent MC. But, most homes and offices in the U.S. will average 6 percent to 8 percent EMC. So, anything you make will undergo serious drying and shrinking after it leaves your plant.
I can think of two options: First, change your markets to more humid climates. Second, build a small room in your plant using plastic sheets for the walls. Put a dehumidifier inside this room along with all your wood. This sealed room with a dehumidifier inside can easily maintain 7 percent EMC 24 hours a day. Move your work out of the room to work on it, but then move it back into the room for nighttime and weekend storage.
In any case, you need to constantly measure MC so that you can avoid any "wet" pieces that will end up giving you a reject in the customer's home or office.
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