Q.
I have some red oak I had sawn, and it has been air dying in an unused tobacco barn (small shed). Can I determine with reliable accuracy its moisture content (MC) by weight rather than the use of a meter? If so, how?
A.
Here is how you measure MC by weight.
Take a piece of wood, cut off about 10 inches from the end (or more), and then cut a MOISTURE SECTION, from that piece, full width, full thickness, and about 1 inch, along the length of the lumber. (With a 7-inch-wide piece of 4/4 lumber, the MOISTURE SECTION would be 4/4 x 1 x 7.)
Take the moisture section and weigh it. Then oven dry it until it stops losing weight (24 hours, plus or minus). Weigh it again. Then oven dry it for another hour or two and weigh it again. If the two weights are the same, it can safely be considered truly oven-dry. Now, you're ready to figure the MC.
MC is calculated as the amount of water lost (the difference between the two weights), divided by the oven-dry weight. That quotient is then multiplied by 100.
For example: Wet weight is 120.00 and oven dry weight is 99.99, then the loss is 20.01. The MC is 20.01 divided by 99.9, which equals .200. You then multiply by 100 to get it into percent form, since we always talk about "percent MC." (So the answer, in this example, is 20.0% MC.)
Typically a MOISTURE SECTION is about 100 grams, so you need a balance that weighs to 0.01 grams if you are to get the most accurate readings. However, 0.1 is fairly close (within .2 percent MC usually).
I suggest a balance rather than a scale.
Gene Wengert, forum moderator
