![]() ![]() The simplified chart to the right shows the EMC values of wood when stored at the humidity and temperatures indicated.Ĭomplete EMC levels for wood stored in unheated structures in your area of the country can be found HERE. For woodworkers and carpenters, the EMC is more helpful than RH. The EMC helps us understand the response wood will have to relative humidity, whether it will shrink or expand. For example, if wood at 10% MC is exposed to 25% RH, the wood will dry to 5% MC (and shrink as it dries). If you’re installing wood that’s recently been transported, or installed on a job, it might take a little while for the material to reach its equilibrium moisture content (EMC) with the air-in other words, for the wood to accommodate to the humidity level for the climate around the wood: the wood may take on more moisture or it may dry out. The higher the relative humidity, the higher the MC of the wood. The moisture content of wood is tied directly to the relative humidity of the surrounding air. Understanding Equilibrium Moisture Content This relationship is referred to as Equilibrium Moisture Content (EMC), and can be accurately predicted. As humidity increases, the MC increases, and the wood expands, and as the humidity decreases, MC decreases, and the wood shrinks. Wood is hygroscopic, which means its MC will fluctuate based on the relative humidity (RH) of the surrounding air. Plus, with this data, finish carpenters can accurately predict how trim and flooring will behave after it’s installed. It’s our premise that with a moisture meter and an understanding of wood movement, most wood movement problems can be avoided. But few realize that the expected movement can be accurately predicted and potential problems avoided. Most finish carpenters are aware that seasonal changes in humidity cause trim and flooring to shrink in the winter and expand in the summer. In this article, we’ll explain the importance of understanding wood movement, how to use a moisture meter to measure the moisture content (MC) of trim, how to decide when a load of trim should be rejected, and how to accurately estimate how much trim will move after it’s installed. (with Gene Wengert, The Wood Doctor.) Expected movement can be accurately predicted, which means avoiding potential problems down the road.
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