Dark Core in Soft Maple
A kiln operator finds that his maple boards develop a light surface and dark core. Others weigh in with thoughts and advice. August 31, 2005
Question
Most of the soft maple, both red and silver leaf, that we have been drying ends up having dark core and white shell. I have a 100-87.5 start with a gradual temp increase and EMC decrease and about 450 fpm across the load. This has been found in air dried, partially air dried and green off the saw. I have followed the suggestions in "Drying Hardwood Lumber" for reducing chemical stains, but it does not seem to make a difference. Does anyone have suggestions?
In these same soft maple charges, we are getting occasional boards that are grey. I think that these are probably log or pre-stacking problems. Is this correct?
Forum Responses
(Sawing and Drying Forum)
The dark core in maple is from not getting the lumber dried quickly enough. The dark core can also be accentuated by too high temperatures in the kiln. High air flow, low kiln temperatures and low EMC's will help combat the problem. I believe that this will take care of your grey boards, as well. One other thing - are you getting the settings that you think you are in your kiln? It never hurts to check the calibration of your kiln controls.
From Gene Wengert, forum technical advisor:
I agree. Often, the core is dark because the shell was dried quickly and then the core was dried more slowly and at a much higher temperature than the shell. Have you tried the schedule suggested in Drying Hardwood Lumber? Also, you indicated the schedule, but not the actual conditions in the kiln. The lumber, of course, only knows what you actually get in the kiln.
From the original questioner:
Thanks for your input. I always get at least a 10 depression in the first 2 or 3 hours and usually hit the set within 12 hours. I looked at the T5-C5 "white wood" schedule that is in Drying Hardwood Lumber, but was concerned that the 120 start may lead to some surface darkening. Are my concerns unfounded? I really don't want to lose the surface white that I get now.
From Gene Wengert, forum technical advisor:
All dry-bulb temperatures are maximums. You can always go cooler.
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