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Forum topic by Pizzadave posted 03-12-2018 09:48 PM 614 views 0 times favorited 5 replies Add to Favorites Watch
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125 posts in 1004 days

03-12-2018 09:48 PM

Topic tags/keywords: walnut cupped slab

Hello everyone, I have a nice piece of slab walnut that I was going to use as a table top. Moisture was around 20% when I got it and brought it inside next to my wood stove. . Moisture level was around 6 after about 3 weeks or so. When I took it to my shop(in the garage) I planed it and it was flat. I left it for a couple of days and I noticed it was cupped pretty bad. I’m assuming it was due to going into an environment with more moisture than by my wood stove. It has sat for a few more weeks and I got a new planer. When I planed the board flat, I’m noticing it’s trying to cup again. What gives??

-- Dave, NY, It works-It really does!

5 replies so far

View ArtMann's profile


1483 posts in 1738 days

#1 posted 03-12-2018 11:42 PM

It takes months or years to dry a thick slab of wood uniformly all the way to the middle. Trying to dry it quickly with a high heat source can do more harm than good.

View Pizzadave's profile


125 posts in 1004 days

#2 posted 03-13-2018 12:35 AM

Ya. Thanks. I learned my lesson.

-- Dave, NY, It works-It really does!

View msinc's profile


567 posts in 1426 days

#3 posted 03-13-2018 01:22 AM

Ya. Thanks. I learned my lesson.

- Pizzadave

Which is not to say you cant do the exact same thing with another piece of wood and have it work fine….but, I wouldn’t necessarily bet on it. “What gives?” well, a couple of things…first off as Mr. Mann has stated it takes years to air dry a piece of slab. They say one year per inch and I have found that to be about right. Some woods, those that are more porous will dry sooner. Others, the very hard dense ones will take longer.
Second, setting a slab in a high heat environment will dry the surface so you will see 6% on a moisture meter. Cut the slab in half {not really, just sayin’} stab it in the middle, that you can now access, and see 20-24%.
Third, wood pretty much does what it wants to and what I have found is that when a board bows or cups even if it is pretty dry it will continue or is very likely to. The boards that are straight to begin with and don’t cup or bow usually continue to remain pretty straight.
I don’t know why one board will warp or bow, but I have four big thick wild black cherry slabs that all came from the same tree. In fact, you can see they are all sequential. three have remained perfectly flat and straight for two years now, one has cupped pretty bad. Again, not just same tree, same parts of the trunk side by side. You can tell by the grain, they all look identical. What caused the one to cup I cannot say. All four were air dried in a waterproof steel building that gets fairly hot inside in the summer.

View Pizzadave's profile


125 posts in 1004 days

#4 posted 03-13-2018 02:01 AM

That makes sense to me man. Thanks a million everyone. The kiln dried slab came out beautifully. I know now to not rush the drying process unless I use a kiln. Also very good to know that once a piece of wood makes up its mind, it sometimes won’t change its mind. I will always remain teachable.

-- Dave, NY, It works-It really does!

View therealSteveN's profile


6691 posts in 1496 days

#5 posted 03-18-2018 04:13 AM

You already know the closer to a standing tree the higher the moisture content. It will dry from the ends, sides, and faces first being “outside” The inner portion retains wet longest.

Any time you remove the “outer” you expose the wetter “inner”

So you want to make sure you remove the same amount of “outer” from each side so both sides end up the same amount of wet. To some extent the same works for edges too.

Failure to do so is the quickest way I know to turn a reasonably flat board into a snake. Twist, turn, cup, curl, you name it, it will happen.

Then there are several rules about drying wood. You must sticker it to allow for proper air movement all the way around it when it is wet. This can be wet from felling the tree, or that wet you get when you open up a board, and start to thickness it, stacking wet to wet is frowned upon, and will yield inconsistent stock.

Already mentioned is heat, and time, but that is a science, ask any guy who builds a home kiln :-)

Slow is the best for a home guy, done in a consistent temperature that you wouldn’t mind being in.

If it is brand new green wood, first thing to do is seal the ends grain. Already mentioned it will dry quickest from end grain, as the wood dries quickly cracks and checks will occur, sealing the end grain with a product like Anchorseal gives the best results, but even paint can help. A 2” deep check sure beats a 4’ one, when you will have to chop it off the end of the board and it’s usually not great product.

Many suggest not trying to dry really wet wood indoors, but will stack it outdoors, off the ground with a good tarp on the ground to discourage bugs. Sticker this pile, and put a top just over the top of it. Starting in the early spring like that you could take it to a kiln, or start air drying indoors at the end of the summer.

Some will do a seal a meal approach where they do all of the steps above, but wrap the wood in black plastic. I personally have not had good luck with that method.

Most suggest an inch per year, up to 3 inches thick, and then they start adding years. Some guys in the south say they get it faster. I’m in Ohio, and those are our numbers. Down South it is warmer, so they are probably correct.

The kiln deal is usually money well spent, if you really like the boards you have. Wood not so special, hey try it yourself. Air dried properly leaves a very usable product.

-- Think safe, be safe

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