Cupping and splitting in slabs

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Forum topic by DirtyMike posted 10-13-2016 07:23 PM 244 views 0 times favorited 7 replies Add to Favorites Watch
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384 posts in 324 days

10-13-2016 07:23 PM

Hello all, I just left my local wood supplier where they carry large slabs and dimensional rough sawn lumber. I noticed that all of the slabs were cupped pretty bad some over a 1” for a 24” wide slab. Most of the rough sawn dimensional hardwoods had deep wide cracks near the ends of the boards and were cupped too. I ask the gentleman that was running the store if the ends of the lumber was sealed, he said he didn’t think so but couldnt answer for sure. He also assured me that the kiln dried lumber wasn’t over 12% MC, I would hope that the air dried lumber wouldn’t be over 12%.

Is the splitting and cupping caused by lack of sealant and poor stickering/stacking?

7 replies so far

View gargey's profile


396 posts in 197 days

#1 posted 10-13-2016 07:47 PM

The list of possible causes is well known. They specific cause in your case is unknowable.

View ki7hy's profile


431 posts in 161 days

#2 posted 10-13-2016 08:23 PM

A lot of this is caused because they are slabs, which still include the pith (in some of them). Sealing the ends would help as well but mainly stickering and stacking with lots of weight would have helped more. The most help would have been to quarter the slabs and then sticker, stack, and add weight.

Species of tree also factor in. Just my thoughts. I might have missed something.

View Bill White's profile

Bill White

4408 posts in 3382 days

#3 posted 10-13-2016 08:45 PM

Find a new supplier.


View DirtyMike's profile


384 posts in 324 days

#4 posted 10-13-2016 08:53 PM

Thanks scott, I knew the nature of a flat sawn slab is to cup but it just shocked me how much material would have to be removed to make a table top. All of the slabs were air dried vertically, And bill i am currently trying to find a good experienced supplier.

View WDHLT15's profile


1565 posts in 1898 days

#5 posted 10-14-2016 01:37 AM

Drying too fast in thick slabs leads to cupping and splitting. Slabs need to be dried in a herd, that is, stickered in a stack like regular 4/4 lumber, in layers with the top layer protected from direct exposure, like with a top layer of low grade lumber to act as a nurse layer. This leads to slower, more even drying. Any slabs that I have dried singly and vertically, like standing or leaning against the wall of a barn or shed have all had major issues like cupping, cracking, splitting, and warping.

My sense is that your supplier is drying the wood poorly.

-- Danny Located in Perry, GA. Forester. Wood-Mizer LT40HD35 Sawmill. Nyle L53 Dehumidification Kiln.

View customsawyer's profile


10 posts in 107 days

#6 posted 10-14-2016 12:16 PM

Drying incorrectly is causing some of the issues. Not reading the log correctly when sawing is going to effect it as much if not more. There are ways to saw the log that will minimize cupping and cracking. Some woods/logs will behave badly regardless of how you saw them.

-- In middle Ga. I run a couple of LT70 mills, edgers, Nyle L200 kiln, Pinhero M800 4 sided planer, and lots or rolling stock.

View kryptix's profile


13 posts in 13 days

#7 posted 10-14-2016 01:25 PM

That said, you might not have to lose as much as you think since you can cut the slab in half, flatten, then rejoin the middle probably only losing about 1/2 – 1 inch in width…

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