Q: We have some incipient decay in our lumber and I'm wondering about including this in the strips from the rough mill. What do you think?

 

A: Incipient decay is the early stage of decay in which the disintegration hasn't proceeded far enough to soften the wood or to cause a perceptible reduction in hardness. Lumber with incipient decay is also called spalted lumber and may have value to hobbyists. Incipient decay in most cases is caused by the white rot fungus, which typically develops because logs were stored in the woods or mill yard in warm weather for several months.

If you do find incipient decay in your lumber when it is in the rough mill, your employees should be instructed to eliminate all incipient decay. This is because strength properties, such as toughness and impact strength, are appreciably reduced in wood with incipient decay, but indications of such losses are not normally visible to the naked eye. The U.S. Forest Products Lab's "Wood Handbook" states, "No method is known for estimating the amount of reduction in strength from the appearance of decayed wood. Therefore, when strength is an important consideration, the safe procedure is to discard every piece that contains even a small amount of decay."

In addition to strength losses in lumber with incipient decay, the sanding dust from such infected lumber may also present allergy problems to some people.

More generally, because incipient decay results from improper log handling, you'll find some mills will have such decay fungi and others will not. The lumber buyer should work with the offending mills to eliminate such lumber from your supply.

 

Q: We tried to glue some jatoba (Brazilian cherry) and it was a complete failure. The joints had almost no strength. We also had lots of trouble with machining, with lots of burn marks. Any suggestions?

 

A: This wood does glue fairly well, but its main problem is that it is very high density, 15 percent to 20 percent heavier than oak. It also has interlocked grain (grain angle changes from year to year). As a result, it's hard to machine a true surface. Further, with such high density, it's easy to burn (or burnish) the wood when tools aren't really sharp (I prefer HSS that is sharpened often rather than carbide). Therefore, with a poor surface, gluing will not be easy; that is, gluing is nearly impossible. It's also important to have a freshly prepared surface.

In short, proper machining will give good gluing. Although some of the common cross-linking PVAs will work well, I would prefer PUR.

 

Q: Where can I locate a very complete listing of most of the exotic woods of the world, which specifically lists specific gravities, densities and weight-per-board-foot. I'm currently building up a few samples using wenge, padouk, zebrawood, purpleheart and bubinga. That is our marketing niche using the highest quality exotics at affordable prices.

 

A: A great deal of information about native and some foreign species is contained in the "Wood Handbook," which was written by the U.S. Forest Products Lab in Madison, Wis. It is available online (www.fpl.fs.fed.us/documnts/fplgtr/fplgtr113/fplgtr113.htm) or in many bookstores. Another good book with color pictures and quite a bit of information about the tree and wood is "A Guide to Useful Woods of the World." This was prepared by the International Wood Collectors Society and is available through the Forest Products Society ( www.forestprod.org ).

 

Q: We've been having a finishing problem. We're seeing differences that aren't acceptable in the way that yellow birch and white birch finish; that is, they don't look the same after finishing. Can you shed some light on this? Thanks.

 

A: White birch and yellow birch are in the same genus, but are different species. White birch is about 12 percent lighter than yellow birch. When a wood is lighter weight, it's generally because the wood is more porous, which will be noted especially on the end grain. But this slight increase in porosity would not greatly affect finishing.

White birch sapwood is creamy white colored while yellow birch has some pale yellow tones in the white sapwood. Perhaps the difference you see is a result of this slight color difference.

However, it's my guess that the differences you're seeing are because of processing differences, not because of inherent differences within the wood itself. Here are three items to check.

If the yellow birch is at a higher moisture content than the white birch, the yellow birch will not be as absorptive. (If yellow birch and white birch are dried in the same kiln load, it would be likely that the white birch would be over-dried unless special precautions were taken.)

If dried by two different suppliers, it's possible that one supplier is using higher kiln temperatures than the other. Heat reduces absorptivity and darkens the color of the wood. Such color changes are usually not seen until the wood is finished.

Because of the higher density, the yellow birch may be burnished more by the planer knives, sandpaper or other tools, especially if dull knives, dull sandpaper or carbide knives are used. The heat generated with dull tools and the burnishing both reduce absorptivity.

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