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 I’ve 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. It’s 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.
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.
