fdmonline.com
Gene Wengert
wooddoc@uwalumni.com
Q:We are using southern yellow pine for furniture and have been getting what looks like length- wise shrinkage. However, I was always taught that wood does not shrink along the grain. Can you help please?
hyde after gluing and this formaldehyde is released from the joint over time. I see these designations used in imported ply wood, including Chinese plywood.
For health reasons, very low emissions are desired. E0 has an emission level of under 0.5 milligram per liter of air; E1, under 1. 5; and E2, under 5.
For some imported plywood, one might question the reliability of the ratings; in other words, did someone actually measure the levels as required to meet the standard? I have seen imported plywood that is supposed to be E1 but there are no markings to indicate this or any other quality stamps. It makes me wonder.
A:I have also heard many times that wood does not shrink lengthwise an appreciable amount. But there are several exceptions to this statement.
First, wood around the core of the tree, often called juvenile wood, does indeed shrink lengthwise several percent from green to dry. As a general rule of thumb, consider this shrinkage to occur in the first 15 to 20 annual growth rings from the center of the log.
Second, with softwoods, compression wood will shrink lengthwise several percent during drying. Compression wood is identified by its darker color and by the oval shape of the stem and wide growth rings in the location of the compression wood.
Special note: Hardwoods have juvenile wood and tension wood (not compression wood) that shrinks several percent upon drying.
Q:When grading hardwood lumber, can incipient decay be included or not?
Q:I am buying some plywood and it is designated as E1 and E2. What is this?
A:The designations of E0, E1 and E2 refer to a European standard of formaldehyde missions. Formaldehyde is a chemical used in many ply wood adhesives. Sometimes there is extra formalde-
A:First, incipient decay (usually seen as a bleached white area surrounded by black zone lines that looks like someone doodled with a marker on the lumber) is caused by a decay fungus, but when using the word incipient, meaning beginning, we assume that the decay has not gone far enough to soften or impair the hardness of the wood.
Second, the NHLA Rule Book states (Rule 26) “stain, including spots in which the disintegration has not proceeded far enough to soften or otherwise change the hardness of the wood perceptibly, will be admitted in grades of species where the rules specifically state stain is admitted or in the grades of species specifying Sound Cuttings.”
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