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Flattening a Warped/Warping Slab Table

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Forum topic by jbdc posted 02-01-2018 02:28 PM 671 views 0 times favorited 10 replies Add to Favorites Watch
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jbdc

5 posts in 138 days


02-01-2018 02:28 PM

Topic tags/keywords: warp slab table elm

Hello, I was instructed to start a new topic after replying to an older thread about dealing with a warped/warping slab table. I think I’ve got a decent idea on how to handle it, and I’m looking for feedback on my plan below; but I’ll start with some contextual background:

CONTEXT

My wife and I recently got a live-edge 2-inch+ thick slab table from my step-father which was made with stock sawn from an elm tree in the backyard of the family home in which he and my mother still reside. He is an amateur woodsmith and the stock was cut from the log by he and his friend who has a mill.

Suffice to say, he did not allow adequate drying time, nor did he bring it indoors to dry before assembling the quasi-bookmatched pieces of the slab, then sealing the top only, with what I’m guessing is/was a 2-part epoxy.

The results are unsurprising: When we were finally able to move the table upstairs from storage in our basement, it had developed quite the downward concave across the 36” width—crowning about an inch in the middle, and making it impossible to anchor the bolts into the inserts he put in the slab through the steel frame it sits upon.

Luckily, I’m a resourceful guy and figured my way to at least attaching the top to the base: I made a vapor-barrier skirt around the edge of the table, put a wick-type humidifier underneath and some boxes of tile down the centreline on top. Over the course of a few days, it flattened enough to get the bolts into the inserts through the base.

Unfortunately, he only anchored the table around the perimeter (no inserts or anchors down the center of the table), and he used what I’m going to call ‘crappy inserts’:

...and the table went concave again after the humidifier tent was removed. He wants to install more of the same inserts down the centerline, thinking that will fix it; I’m almost certain it will not:

  1. That type of insert is dependent upon small screws for holding strength; probably no match for what I expect will be hundreds, if not thousands of pounds of pulling force.
  2. Even if the inserts held, the strain would probably pop his biscuit joins like the seams of a suit too small for a large man.

THE PLAN

I’m already flattening the slab again with the “humidifier tent + tile boxes” method described above. Once flat, I plan to seal the bottom with AnchorSeal or Lee Valley End Sealer for Logs and anchor the slab to the base down the middle with the largest ‘not-crappy threaded insert nuts’ I can find:

I realize those sealants are meant for endgrains in a totally different application, and I’d consider using the same epoxy as on the top, but it’s winter and I don’t have a workshop in which to do the work, and we have an infant in the house—so I’m looking for a sealant which will significantly slow or stop the transpiration of water vapour out of the wood without off-gassing nasty crap to my wife and baby. It doesn’t need to look at all nice; it just needs to do the job given my requirements and not rub off on people’s pants if they brush the underside of the table.

QUESTIONS

Thanks for your time in reading this over, and for any advice!


10 replies so far

View Aj2's profile

Aj2

1421 posts in 1820 days


#1 posted 02-01-2018 02:45 PM

Sounds like a train wreck. I’ve never worked with Elm but my rule with any woods that don’t behave stand them up in the corner of my shop till they settle down. I had some Beautiful Douglas fir that sat for years till it stopped weeping sap and cupping.
Good luck

-- Aj

View rwe2156's profile

rwe2156

2958 posts in 1503 days


#2 posted 02-01-2018 04:38 PM

How long ago was it cut? You’re never gonna get it equilibrated doing what you’re doing.

As you’ve already found, the cup will never come completely out &/or will reappear after you think you’ve solved it. This is because unequal stresses develop in wood that is dried unevenly (this is my theory anyway).

My suggestion is store the slab on stickers in your house for at least 1-2 years. Then build a router sled and flatten it.

-- Everything is a prototype thats why its one of a kind!!

View johnstoneb's profile

johnstoneb

2932 posts in 2195 days


#3 posted 02-01-2018 04:45 PM

All the sealer will do is slow the wood movement. You need to remove all the finish, rip the table top into narrower pieces, let them dry and until the wood and moisture content stabilize. Then square up the stock and start over.

-- Bruce, Boise, ID

View Loren's profile

Loren

10476 posts in 3670 days


#4 posted 02-01-2018 04:47 PM

Is the base slotted to allow the table to
move in width?

I agree with Bruce. I would consider ripping it
down the joint and regluing it. Perhaps once
cut in half the two sides can be rejoined to
form a relatively flat plane. If the two sides
are themselves cupped severely, either they
will need to be flattened and thicknessed or
ripped into narrow boards as Bruce suggests.

View Carloz's profile

Carloz

1147 posts in 614 days


#5 posted 02-01-2018 04:57 PM



All the sealer will do is slow the wood movement. You need to remove all the finish, rip the table top into narrower pieces, let them dry and until the wood and moisture content stabilize. Then square up the stock and start over.

- johnstoneb


I am curious why ? Do narrower pieces ( not as narrow a half inch or so ) dry any noticeably faster than one whole piece ? If you talked about thinner pieces with the following lamination that could be a different story.

View Woodknack's profile

Woodknack

11768 posts in 2402 days


#6 posted 02-01-2018 05:33 PM

Wood movement is hydraulic so its almost impossible to force a slab to stay flat. I would try your plan of flattening the slab again and sealing the bottom, might work, might not. But it’s easy to try. General rule with panels is that what you do to one side, you do to the other. If that doesn’t work then you’ll need to take more drastic action. But I would try the easiest thing first.

-- Rick M, http://thewoodknack.blogspot.com/

View OSU55's profile

OSU55

1694 posts in 2012 days


#7 posted 02-01-2018 10:56 PM

Are there any fundamental flaws with my plan? Unfortunately it is severely flawed. Until the wood dries out, it will move any which way. Trying to restrict it will result in something breaking, bowing, cupping, who knows. Get the top off and replace it with a piece of plywood or something, strip the finish, and let it sit around for a year or 2.

Are the inserts I plan on using the correct type? Possibly, but probably not. Even after the wood is dry, it will move with moisture change. The top has to be attached allowing it to move.

Is my planned sealant appropriate, or are there better options I’m unaware of? No, those sealer products will rub off on clothes. Once the wood has dried, been reworked to flat and the panel glued again, finish both top and bottom.

Would Titebond wood glue work just as well as AnchorSeal? Actually better since it wont rub off, but don’t do it until the wood is dry.

Other thoughts or ideas? Not until the wood dries. You will just be chasing your tail in circles until then. It’s just not worth fighting it. You could build a “tent” and use your dehumidifier to dry the wood faster. The existing finish needs to be removed. Too fast and you could create large cracks etc.

View jbdc's profile

jbdc

5 posts in 138 days


#8 posted 02-02-2018 09:44 PM

Thanks all for the feedback; in the interval I got some additional information: The sealant is water-based Varathane; So, not nearly as bad in terms of VOCs etc. as epoxy or oil-based sealants. I may simply send wife and baby away for the day when it gets warm enough outside for me to put a box fan blowing out the window, then seal the underside with the same number of coats applied to the top (maybe a few more since the top could do with a few more layers too).

I have no expectation that the inserts will prevent the table from warping entirely; the hope is that they’ll provide an extra bit of stability as the sealant helps slow and even-out the diffusion of water out of the wood over a longer period. (Like using low-power settings on the microwave to avoid pockets of ice and lava in a burrito.) I understand that without sufficient drying (and even then), the wood will continue to move. The existing anchor holes in the base are already oblong (whether that was by design or a fudge, I don’t know); and the anchors will only be lightly tightened.

Further, I know I may be on a fool’s errand, but I’m trying to make the best out of an unfortunate situation with what little resources and time I’ve got: There are countless little projects as we transition our century home from 3 apartments to a more conventional home + basement suite.

That said, I’ll try to keep all your helpful advice in mind as I put this plan into action to ensure that I don’t prevent myself from being able to take some of the more comprehensive measures you guys have suggested in the future.

I’ll post some process photos soonish, and I’ll follow-up with updates in the longer term.

Again, thanks to everyone who’s contributed thus far!

View Gene Howe's profile

Gene Howe

10521 posts in 3451 days


#9 posted 02-02-2018 10:52 PM

I’ve seen 8/4 elm, dried to 6% , cup. And it was coated on both sides with epoxy. Elm is just plain ornery.

-- Gene 'The true soldier fights not because he hates what is in front of him, but because he loves what is behind him.' G. K. Chesterton

View rustfever's profile

rustfever

752 posts in 3332 days


#10 posted 02-03-2018 12:15 AM

Throwing good money after bad!
Do it right or forget it.
Rip into smaller boards, sticker, air dry for as long as it take to get equilibrium.
Glue up and Watch the Grain.
Plane true and then a good finish on ALL edges.
Or just keep fighting a loosing cause.

-- Rustfever, Central California

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