Spots revealed in dry, planed lumber

Dr. Gene attempts to find the causes of discolored spots on dried lumber, revealed only when the stock has been planed. 1998.

Professor Gene Wengert

Have you ever heard of a spray in the later part of a schedule causing funny discoloration on hard maple? These spots look like oil spots and can not be seen until surfacing. They are very few and we haven't established a pattern as of this time but feel strongly it is from our drying process. When the sprays come on the reservoir fills and doesn't drain fast enough to keep water from coming out the header and wetting the wood.

Could this be causing the spots? We have new American package kilns pushing air through 14" of wood. We treat our water with Nalco chemicals and our water source was recently treated with chlorine.

The spots could be from several sources---they could be because of water on the surface (rain or snow) that doesn't let the interior dry fast enough, and so the wood develops interior chemical stain.

They could be spots where a lumber fungicide resulted in penetration by certain discoloration chemicals due to the surfactant in the solution. Or it could be the pH of the dip solution is a factor.

They could be spots where the boiler water (not steam) dripped on the lumber.

In most cases, the quick drying of the surface leaves the surface color in good shape, but subsequent surface treatments/events discolor the interior.

We do not see these spots with fresh logs and quick drying. Look for a problem at MCs over 40% MC.

Why are you steaming at intermediate stages of drying--steam should not be required until equalizing and conditioning?

Professor Gene Wengert is Extension Specialist in Wood Processing at the Department of Forestry, University of Wisconsin-Madison.

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