Air Drying Lumber
Freshly milled, or green lumber has a high water content. For some uses, this is OK, but if the wood is going to be used indoors most of that water will need to be removed.
Fortunately, getting rid of the water is not difficult. It evaporates. For both lumber and laundry, the process is called drying. In either case, there are two options: quick drying in a heated appliance (called a kiln in the case of lumber) or air drying outdoors. Air drying takes longer, of course, but requires no energy other than what we get for free from the sun and the wind. So, there's both a cost savings and an ecological benefit to this approach. In most cases, the end product will be pretty much the same either way.
Air drying requires good air circulation. In the case of lumber, this means that stacks need to be built in a way that allows air to move freely around the individual boards and carry the moisture away. This is done by stacking boards in layers separated by spacers called stickers.
Lumber should be sticker-stacked soon after milling, within a few days in most cases. Failure to do so may result in staining of the lumber which is caused by microorganisms or chemical reactions in the wood.
There's no shortage of information available about how to properly build a stickered stack of lumber for air drying. Rather than trying to summarize it here, there are links below that you can follow to read and listen to people who know what they're talking about. Of course, they sometimes disagree with each other on the details...
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Drying Native Lumber (pdf, 482 KB) is a brief 5 page description of both kiln drying and air drying procedures. It comes from the Vermont Department of Forests, Parks, and Recreation.
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Air Drying of Lumber (pdf, 4,460 KB) is a 66 page report from the US Dept. of Agriculture aimed at large commercial operations, but it still has a lot of useful information for the rest of us. In particular, there's a chart on page 24 which shows the approximate time to air dry 1 inch thick boards of various species of wood.
Unfortunately, the drying times are in broad ranges. For instance, Northern Red Oak will dry in 70 to 200 days. The reason for the large range is that lumber, like laundry, will dry much more quickly in summer than in winter.
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A Calendar for Air-Drying Lumber (pdf, 21 KB) is another USDA publication that can help in making better estimates of actual drying times by taking seasonal variations into account. It contains a chart that estimates the number of effective drying days in each month.
One inch Red Oak takes 70 days to air-dry in the best of conditions. The calendar chart in this document tells us that drying for the warm month of June will count for 30 days of the 70 needed. But, drying for the cold month of January would count for only 5 days of drying.
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How to Dry Lumber is a 10 minute video hosted on the website of Fine Woodworking magazine. You will need the Adobe Flash Player to view this.
As several of these resources point out, air drying outdoors will not dry lumber quite enough for indoor use. To complete the process, simply bring lumber into a heated space for a time.
If you don't have a moisture meter to measure the moisture content of your lumber, you can use the oven in your kitchen and an accurate scale instead. The technique is described in detail on page 14 of the Air Drying of Lumber publication.