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Name: Robert B.
Status: Student
Age: 17
Location: N/A
Country: N/A
Date: Febraury 2003


Question:
I was once told that the native Americans would "roast" their spears over a fire to make the wood stronger. Is it true that heating wood or burning it to a certain point makes the wood stronger?



Replies:
I do not know much about what the native Americans did with wood, but it seems very plausible. The following advantages of dried wood are given in the USDA Forest Service publication titled Drying Hardwood Lumber:

"Some advantages of dried lumber over undried or partially dried lumber are as follows: - Lumber with less than 20% maximum moisture content (MC) has no risk of developing stain, decay, or mold as a result of fungal activity.

- Dry lumber is typically more than twice as strong and nearly twice as stiff as wet lumber.

- Fasteners driven into dry lumber, including nails and screws, will perform much better than do fasteners in wet lumber, especially if the wet lumber dries after fastening.

- Dry lumber weighs 40% to 50% less than wet, undried lumber. For example, an 18-wheel, flatbed truck can haul about 7,500 board feet of wet lumber, 10,500 board feet of partially dried lumber, and 12,500 board feet of kiln-dried lumber.

- Products made from properly dried lumber will shrink very little or none at all while in service; products made from wet lumber often shrink substantially as the wood dries.

- Gluing, machining, and finishing are much easier to accomplish with dry wood.

- Wood that will be treated with fire retardants or preservatives (such as copper chromium arsenate, CCA) after drying must be at least partially dried to allow for quick penetration of the treating chemicals."

So, it is pretty obvious that drying of wood imparts some very positive properties, included increased strength, reduced weight, and less tendency to warp or shrink as it ages. If you would like to learn more about the actual mechanisms that improve the wood through drying, you can visit the web site of the Forest Service's Forest Product Laboratory at the University of Wisconsin. Their address is www.fpl.fs.fed.us. Go to their publications link to download the publication on hardwood drying and many other informative handbooks.

Andy Johnson



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