Protecting Cabinets from Changing Humidity

      Details on how shop humidity, jobsite humidity, and occupied home humidity vary, and advice on helping cabinets withstand the changing environment. January 21, 2007

Is there a perfect shop humidity level? Does anyone have problems with laminated goods going out of the shop in the cold season, when the heaters are on, and then getting installed in a different environment? Building on site or letting materials acclimate is not an option. The shop is at around 22%-25% humidity at this time. We took a fairly large top out of the shop yesterday, and today went on site to finish up. I noticed that instead of feeling the top laminate overhanging the edge as though it was not filed properly, you could feel the top of the edgeband as though the deck had taken on moisture and swelled the edge out. It was slight, but in the shop the top was perfect. Was it a fluke? Typically when a job goes in, we are in/out same day and don't see it again.

Forum Responses
(Cabinetmaking Forum)
From Professor Gene Wengert, Sawing and Drying Forum technical advisor:
We all know that wood changes its moisture when the surround RH changes and that changes in size occur when the moisture changes. Form this perspective, an RH of 20% is about 4% MC in wood (the air is said to be at 4% EMC). Most homes in the winter heating season will reach about 30% RH (unless humidified). Showers, plants, and cooking with less fresh air than a shop using a dust system mean that homes tend to be higher in RH than a heated shop. In the summer many homes will reach 50% RH average. These two values are 6% EMC to 9% EMC. The outside conditions in North America in most of the country are 65% RH average or 12% EMC. The best shop environment is one that is identical to the home or office into which the furniture is going. Oftentimes in a small shop we control RH by avoiding excessive heating. Larger shops will add humidity and recycle dust collector air. Only a few shops are climate controlled year round.

From the original questioner:
Gene, obviously the best solution is to match the environment of where the product is going. But what to do if one day's job is going to a heated home, the next to an unheated business under construction, the next for pick-up and who knows where? I am mainly curious if this is something that can be monitored/solved, or is the way it is.

From Professor Gene Wengert, Sawing and Drying Forum technical advisor:
Even an unheated space under construction will eventually be heated, so I would target the expected final MC. To minimize changes between manufacturing and use, consider putting an item in a plastic wrap. For example, it takes 2 pints of water for a 100# door to change 2% MC, and usually 2% MC is considered a "safe" change. So, wrapping the door in plastic wrap is very effective. So is coating the wood on all six sides with a vapor resistant coating such as several coats of marine spar varnish. Note that wood products stored in a tight container will not change MC if there is very little influx of moisture. Temperature alone is not important.

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