Revert cupping in sheet goods with wood glued on top?

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Forum topic by davidwww posted 12-02-2021 02:58 AM 336 views 0 times favorited 3 replies Add to Favorites Watch
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19 posts in 154 days

12-02-2021 02:58 AM

I’m making some centerpiece/serving trays for my sister to sell. I decided I’d plane lumber down to 1/4” thick then glue it in small geometric pieces to different substrates (MDF, plywood).
All was going well for the last few days, and I even managed to work some warp out of some of the sheet goods I was working with by gluing the pieces on (combo of CA and TB2). However, when I got home today after leaving them all inside overnight, they were all horribly cupped – all four corners raised up . Some not as bad, some a bit worse, one of them really badly.

This makes getting my side pieces attached pretty complicated, and also makes me worried for what’s going to happen once these go to slightly different climates around the state.

Can I just add moisture and clamp with some cauls? Or how can I counteract this, and what I can I do to prevent it in the future?

3 replies so far

View Loren's profile


11374 posts in 4986 days

#1 posted 12-02-2021 03:43 AM

First I’d try exposing both sides evenly to airflow for a couple of days. This probably won’t help but it’s worth a shot. You can stack and sticker them if you want to, putting a weight like a cinder block on top.

If that doesn’t work you can try moisturizing the concave side so it expands.

In the future you need to add a layer of wood to the opposite side of the substrate. I don’t know if you can get away with a thin layer of veneer or if solid wood of comparable thickness to the top side will be needed.

View Lazyman's profile


8834 posts in 2726 days

#2 posted 12-02-2021 12:03 PM

Even if you are able to get them flat again using moisture, it may just happen again so I would be hesitant to sell them with this in mind. Several things could have contributed to this. The TB glue might be part of the reason it happened. It added moisture to the glue side that hasn’t exited yet but the top dried out some. It could just be that that the wood wasn’t completely dry or at least acclimated to your indoor environment after planing. How long after planing the wood did you wait before gluing them down? You should wait several days (I would probably wait a couple of weeks) with the wood stored so air can circulate around both sides after planing to let everything settle down and make sure that there is no warping before using it. I don’t know how many times I have planed wood and left it sitting flat on a work bench for a couple of hours only to find that it cupped because air could not get to the underside. Even so, you may get better results using a 1/16” thick veneer rather than the 1/4” thick wood.

-- Nathan, TX -- Hire the lazy man. He may not do as much work but that's because he will find a better way.

View bondogaposis's profile


6105 posts in 3689 days

#3 posted 12-02-2021 02:42 PM

The problem is in gluing solid wood, an unstable material, to a stable substrate like plywood. The wood will move in response to humidity, the plywood will not. This is not a viable way to construct something. You would be better off making the entire piece out of solid wood.

-- Bondo Gaposis

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