Surface Checking in Walnut

      To control surface checking in Walnut, you have to tweak the air-drying process. July 7, 2011

Question
I just pulled a pretty large bunk of expensive 8/4 walnut out of my kiln to find out the surface was really checked! I was able to plane down to 1 1/2" and get rid of most of them, but still its ruined a ton of lumber I really needed to sell. What gets me is that it was air dried for over a year and a half before being put in my Nyle kiln. I did have the Nyle on pretty strong right away, but my feeling is that this damage happened by drying to quickly from green? I take precautions with my QSWO by wrapping with landscape fabric so it doesn't dry too quick and check while air drying, but Iíve never had problems with walnut before.

Is it possible this happened while air drying? Can you air dry too long? It might have been two years. The kiln was on 100% compressor cycle at 120 degrees which is my normal rate for air dried lumber. Then a 24 hr cycle at 150 with humidity to condition. I never had this before. Itís concentrated on knots and figured areas, but also in the middle of perfectly clean lumber

Forum Responses
(Sawing and Drying Forum)
From Gene Wengert, forum technical advisor:
Checking occurs above 45% MC, so you have air drying checks. They worsen and stay open at the end of drying if they are subject to rewetting when partially dry. Start a kiln with the same EMC as the outside EMC - usually 12% EMC. If you start wetter, it will make small checks worsen. With your long air drying, you have an air drying issue.



From the original questioner:
Thanks for the info. Wound you suspect that I should use fabric to slow the drying on my 8/4 walnut like the QSWO? Maybe it was unusually dry and windy when I stacked it green.


From contributor A:
Most of the time walnut is forgiving but if thick stock tries to dry to fast it will check badly. I try not to saw it during the heat of summer unless I am going straight into the kiln with it. That way I can control the humidity.

I often sticker it and cover the whole pile with black plastic. This keeps it from being re-wetted by rain and keeps the humidity high for a few weeks. The pile gets hot during the day and helps dry the thicker stock faster. During the summer dead stack it and cover with black plastic and it will make the lumber look like it was steamed after a month or two.



From the original questioner:
Thanks, I'll try it. Yes Iíve noticed on old walnut logs left around for awhile that the sapwood starts to turn darker. I don't know if it matches well enough so that people will actually pay for it, but it does look closer after awhile.



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