Un-Cup a Glued Panel

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Forum topic by ckorkyrun89 posted 11-30-2015 05:31 PM 885 views 0 times favorited 14 replies Add to Favorites Watch
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65 posts in 2018 days

11-30-2015 05:31 PM

I have 4 panels that I have glued together out of ~12” wide Sapele. Each panel is ~24” x ~30” with ~1/4” cupping across the 24” direction.

When I bought the boards, they were flat and surfaced on both sides. I suspect that the moisture in my garage is too high and that gluing them one side down towards concrete created an unbalanced moisture situation and that the convex side has expanded due to additional moisture.

Right now, I have them sitting in my house hoping that the moisture will equalize across both faces and I will end up with flat panels again. If this does not work, does anyone have ideas of what I could try? I have read about placing them concave side down in grass, wet newspaper on the concave side, and heating up the convex side. I am willing to try one or more of those, but I don’t have a good idea of the duration of each or if they actually work.

14 replies so far

View a1Jim's profile


117090 posts in 3572 days

#1 posted 11-30-2015 05:42 PM

You can try dampening the concave side with a damp sponge and placing it on stickers with weight on the top,it may take a few tries.
In a worse case scenario you may have to rip it (on a band saw for safety) joint and glue back together.

-- wood crafting & woodworking classes

View rwe2156's profile


2920 posts in 1475 days

#2 posted 11-30-2015 07:12 PM

I wouldn’t be very optimistic about a spontaneous recovery.

I’ve just never had very good luck with the moistening/heating thing.

I’m with Jim on re sawing the panels and resurfacing. I’ve done that before and it works.
I would split the glue lines and also make a cut each panel down the middle making 6”.
Before you glue back up, make sure the grain direction is the same in all the boards.
The problem you’re going to face is the panels are finished thickness and you’ll need to do a very accurate glue up.

For future reference, I always put the panel in plastic bag or wrap it with saran wrap immediately after taking off the clamps.

Good luck!

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

View shipwright's profile


7980 posts in 2792 days

#3 posted 11-30-2015 09:19 PM

Did you alternate the curve in the end grains when you glued them up?

-- Paul M ..............If God wanted us to have fiberglass boats he would have given us fibreglass trees.

View bonesbr549's profile


1546 posts in 3062 days

#4 posted 11-30-2015 09:26 PM

Now this was in summer, but once i had two doors long panels and painted them and left them out to dry and came back and they’d cupped like a son of a gun. I was ready to chuck them in the trash and the wife convinced me to flip them around and leave them in the sun and i’ll be darned they came back. However that was the only time(and I’m old). If they don’t recover, you can rip and reglue, and salvage some of it. Thats one of the reason I llike rough stock and I take it down slowly to avoid. Good luck my friend!

-- Sooner or later Liberals run out of other people's money.

View pintodeluxe's profile


5654 posts in 2808 days

#5 posted 11-30-2015 10:48 PM

Much of the answer depends on what the final use for the panels will be. It they will be installed in a frame and panel, that may straighten them out.

-- Willie, Washington "If You Choose Not To Decide, You Still Have Made a Choice" - Rush

View AlanBienlein's profile


159 posts in 2669 days

#6 posted 11-30-2015 10:58 PM

Go and lay them back on the concrete with the opposite side down. Just keep an eye on them.

View AlanBienlein's profile


159 posts in 2669 days

#7 posted 11-30-2015 11:04 PM

Oh and never lay your panel on a flat surface without some kind of sticker under it to allow for even airflow and to prevent cupping.

View ckorkyrun89's profile


65 posts in 2018 days

#8 posted 12-01-2015 03:09 AM

Thanks for all the responses.

I probably should have said tops instead of panels. I am making a couple of end tables with steel bases and sapele tops. Each top is made of 2 boards with just one glue joint and the boards are essentially quarter sawn. For one, I am trying to avoid cutting the boards into smaller widths since I like the look of just 2 boards. I also didn’t flip the grain (probably foolishly) since they were quarter sawn and I didn’t expect for them to cup.

I’m trying to very lightly moisten one side and heat the other right now. I’ll report back if I get any luck out of that.

I think that in the worst case, if I can get them back to within 1/16” or so of flat, the steel base will likely hold them flat enough that it should work out.

View ckorkyrun89's profile


65 posts in 2018 days

#9 posted 12-01-2015 04:41 PM

Not much luck so far. I will try moistening the concave side a little more and weighting it down to see if I can get any results.

View mahdee's profile


3883 posts in 1762 days

#10 posted 12-01-2015 05:09 PM

ckorkyrun89, I think you are right about the steel holding it in position. If you really want to make the straight, screw or clamp them to the steel base cup up with some shims at the edge of the cup and let them be for a day.


View a1Jim's profile


117090 posts in 3572 days

#11 posted 12-01-2015 05:13 PM

I don’t know if this is something you want to do or are able to do but you can cut kerfs in the wood on the bottom of the table tops by cutting 3/4 of the way through the wood every inch or two and the wood will flatten out. after that you can fill the kerfs by gluing in contrasting wood to make it look like a design choice or wood of the same kind your top is made of or even epoxy.

-- wood crafting & woodworking classes

View ckorkyrun89's profile


65 posts in 2018 days

#12 posted 12-04-2015 08:26 PM

I got some decent results from wetting the concave side and using clamps to try to flatten it out. It is now flat enough that I can live with.

Thanks for the help everyone.

View Tennessee's profile


2872 posts in 2509 days

#13 posted 12-04-2015 08:38 PM

Ha, Jim I did that kerf trick back in the day when I refinished.
Brought back the olden days!

Had a big double drop leaf table that when folded, was no more than 12” wide, but opened to about 6 feet. One of the drops was bent about 3 inches.

The antique dealer had bought it and stored it in his barn over a NE Pennsylvania winter – (not tooo smart!!)
He went to put it in his showroom in the spring and Oh, MY, what happened here!!

So we took it and discussed all kinds of things, including setting angle iron in a groove and letting the flat be screwed to the back, which he didn’t like.
So we kerfed it…Boy, I can tell you that was some nervous cutting! We had to do it with a radial saw so we could see the saw blade cutting since we had that bend to work with. Stained it jacobean afterwards to hide the cuts. Table was almost black from age anyway.

Then we filled it with epoxy and dust from the cuts after straightening. It pretty much worked!
I think it was cherry.

-- Tsunami Guitars and Custom Woodworking, Cleveland, TN

View Todd's profile


398 posts in 1671 days

#14 posted 12-04-2015 11:24 PM

What Alan said. My shop’s humidity and temp are fairly well controlled but every time I stack without shims I get warpage. Ruined a nightstand tabletop that way.

Oh and never lay your panel on a flat surface without some kind of sticker under it to allow for even airflow and to prevent cupping.
- AlanBienlein

-- Todd, Huntsville, AL

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