Troubleshooting Warpage with Kiln-Dried Cherry

Why did a load of Cherry boards warp in the kiln? May 16, 2008

I was given three beautiful 16' cherry logs and had them sawed to 1-1/8". I stickered it and covered with a tarp for 6 weeks. I got it to the kiln and the MC was 16%-18%. The gentleman that owned the kiln said he would have it for six weeks. He called me after three weeks and said it was ready and the MC was 6%. I got it home and stacked it up outside for two days before I got it inside. When I was bringing it in, I noticed some pieces were twisted. Just thought it was pieces that were on top in the kiln. I ended up with 5 pieces out of 400 bd. ft. that were flat. I called him and told him what happened and he told me that he never had this happen and didn't know what to do about it.

Forum Responses
(Sawing and Drying Forum)
From contributor M:
Black cherry will warp if it is not heavily weighted. I lost a 42" diameter log this way. I cut it into 2.5" thick table top slabs. It warped badly as it was stickered and waiting for the kiln to free up, and I did not weight it down. Lost the whole log. I just pulled some 8/4 thick cherry mantel stock out of the kiln. One row curled up about 4-5 inches about two feet from one end. The rows above this point were not as long; this meant the weights on this pack were not bearing down on this last two feet. Lesson learned; weight cherry heavily. What most likely happened is, your stock went on the top of the pack and was not weighted.

From contributor J:
Not that it will do you any good, but the same thing happened to me. I stickered 6/4 cherry with plenty of weight and it air dried flat. They were only 6' long too. Kilned to 6%. I lost every single board to twist! I was able to sell some of it as 4/4 and my good friend heated his house with the rest.

By the way, no one was ever able to offer an acceptable explanation, and in fact, most responses were something like "aw shucks, cherry is so easy to dry!"

From contributor V:
Cherry can be a pain to dry, if the log is from a crooked tree. Most cherry around here seems to grow in fence lines or woods edges, and because of this growth pattern, the grain can get twisted, trunks curl upward with tension wood, trees grow at an angle to peek out and get to light... That's part of the charm of it, I guess!

From Professor Gene Wengert, forum technical advisor:
If the cherry is sawn parallel to the bark and not parallel to the pith, you will get flat lumber. The log must also be sawn so that the rings are centered edge to edge when viewed from the end grain. This involves turning the log after sawing a few pieces and turning it 180 and not 90 degrees. I suspect that the warp is basically a sawing issue. More details are given in the "Sawing, Edging and Trimming Hardwood Lumber" book.

As mentioned, crooked logs will produce warp-prone lumber no matter how sawn. The technical explanation for the warp is that the angle or slope of the grain was not parallel to the faces of the lumber.

Knotty wood also warps more, as you do not have the SOG parallel. Note: Slow drying will also make more warp, so when you covered the load with a tarp, you may have slowed drying too much.