Q. We are getting a lot of information about the correct spacing of stickers when drying and also the 4x4s. What is the best? We dry mostly oak and cherry, but sometimes do have other species. We do make furniture that needs long, straight pieces, so warp is a concern.
 

KNOWLEDGE CENTER

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A. Stickers are almost always spaced 24 inches apart. Sometimes, when there is a lot of odd length lumber (1 or 3 feet shorter than most of the lumber), there will be 12 inches of spacing at the ends of the pile to catch these shorter pieces; that is, a sticker is at the end, then 12 inch, then 12 inch and then 24 inch until the same 12-inch spacing is repeated at the other end of the pile. However, you can safely use 24-inch spacing (by "safely" I mean drying without increasing warp) if and only if your alignment vertically is perfect. Further, the 4x4s must also be aligned correctly and placed under each sticker; that is, 24-inch spacing of the 4x4s as well. Anything less than this preciseness and you will contribute to warping.
 

Closer spacing

 
You can space stickers at 12 or 16 inches. This is sometimes done with higher grades of expensive lumber. Closer sticker spacing is most effective on thinner stock or when sticker alignment is not perfect. With 12 or 16 inch spacing, you can be a bit sloppy in alignment without contributing to warp. A few warp-prone species like sweetgum, will probably benefit from slower spacing for 1 inch and thicker stock.
 

Short sticks

 
I should mention that short stickers (an inch or two shorter than the width of the pile; the ends of the sticker have probably broken because the lift driver had two packs too close together when he lowered the one pack; don’t let this happen) do increase cupping and other forms of warp. These short stickers need to be eliminated.
 
One idea is to cut them back to the next shortest foot and then sell them as short stickers; for example, if you usually use 6-foot stickers, a broken one can be cut back to 5 feet and sold. 
I have heard many good reports on oak, apitong and western-made laminated "plywood" sticks, as well as stickers of these species with a profile designed to minimize staining. These premium stickers are expensive, so it is important that the lift drivers do not break the ends or otherwise damage the stickers. Training of lift drivers in this respect is often overlooked.
 

Side-bend and bow

 
You might be interested to know that side bend warp and lengthwise bow is seldom, if ever, the result of poor drying practices (other than poor stacking). These types of warp are due to the sawing procedures used and the resulting grain deviations in the lumber or due to natural stresses in the tree. (For example, it is common to find that quartersawn lumber will develop much more side bend than flatsawn.) A good sawyer using proper sawing procedures will produce flatter lumber after drying.
 
Putting top weights (perhaps 100 pounds per square foot) on top of the loads can help hold the lumber flat, preventing some bow and side bend, if stickers are aligned perfectly. With poor alignment, top weights will increase the warp. It is not clear if the loss in kiln capacity from these large weights is financially beneficial for all operations.
 

Cup

 
Cupping warp is a natural tendency of flatsawn lumber, as the bark side of the lumber will shrink more than the heart side. This cupping tendency is more for flatsawn lumber sawn from near the center of the log. Cupping (and staining also) is accentuated by slow drying especially at high MCs, rewetting during drying (such as starting the kiln at too high of a humidity after the lumber has been air-dried; usually start at 60 percent RH or even a few points lower) and over-drying (drying under 6.5 percent RH or using a 50F depression).

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