[dsabcan]

I completed a project for a cribbage board/table by laminating thin strips of oak (1/8") on a 3/4" piece of plywood. I applied 3 coats of polyurethane to the oak surface and finished the underside of the plywood with a couple of coats of paint. After a few days the table started to warp, cupping in on the laminated side. What did I do wrong and can this be fixed?

 

[ryan50hrl]

Is that particle board.....doesn't look like plywood.....

 

[Camden]

This is just a thought, but you may want to treat it like veneer work. What I mean by that is, when you put veneer on one side of substrate, you often have to put a "balance" or "backer" on the other side to keep what you have from happening. For instance, a cabinet maker gets an order for some rosewood cabinets. He veneers the rosewood on the front, as it will be seen, but uses a less expensive but similar structured veneer like maple(maybe?) on the back. Now, when the rosewood expands and contracts with seasonal changes, etc., the backer will as well, making the whole piece behave more like solid wood. I'm not sure if this will work for your scenario or not, but it's something. Good luck!

WCT

 

[dsabcan]

Is that particle board.....doesn't look like plywood.....

Yes, it's plywood. I also glued a thin piece of oak edging.

 

[ryan50hrl]

Got ya......That's weird that its happening on plywood. I tend to agree with camden that you'll need to laminate both sides.....Did you put poly on the bottom as well as the top?

 

[frankp]

What camden said. You need to do something to the opposite surface as well.

 

[Steve Neul]

Laminating the underside may have elimated the warpage however the strips of oak are going to expand and contract at a different rate than the plywood substrate. What you can expect to happen is over time the joints between the strips will break open making gaps. The holes also could have contributed to the warpage as you weakened that side of the plywood.

 

[cabinetman]

Veneers in ⅛" thickness aren't that likely to have movement issues that would account for that cupping to happen, as the plywood doesn't have any movement issues. It could have happened because the bottom wasn't veneered like the face. Even though there was a topcoat (polyurethane) on the face, and paint (on the bottom) the surfaces were sealed and less likely to be subjective to moisture issues. It could have just been a piece of plywood that had a mind of its own, and reacted. The polyurethane could have had more "pull" than the paint.

.

 

[Camden]

Cabinet man- I wondered about that as well; never used anything that thick in a "veneer" application, so I was kind of thinking it would be more stable, especially since it wasn't a single piece... I think you hit the nail on the head with the "plywood with a mind of it's own" idea. I've found that unless I use fairly high quality hardwood substrates, they can be pretty unpredictable, especially in such small sizes. Never know what the life of the various elements has seen. If I were to try this project, having seen this, I would think about using a slightly better ply, like a birch or oak, and maybe consider using true veneer(and single pieces) in the 1/42 thickness range. Sometimes there's no accounting. Good luck!

WCT

 

[HowardAcheson]

The oak veneer is trying to shrink--as solid wood will do. The plywood does not shrink so the veneer is pulling the plywood into a warp as the solid wood veneer shrinks.

There's not much you can do about it now. If you rebuild, use a thinner veneer and veneer both sides of the panel. Also, be sure that you environmentally condition both the veneer and the plywood before assembly.

 

[woodnthings]

Plan B

Saw the thing apart down the lines of the cribbage board, and maybe in 2 other places. This will be a challenge because of the round shape, but here's what I would do. Attach it to a 1/4" or 3/8" thick rectangle of plywood such that the lines inside are parallel to the edges of the board. Using a table saw and the fence, just rip the round into several sections.

Now the "tricky" part is getting a good edge to glue them back together, since there will be a very slight angle to them. I would probably use a jointer or a hand plane if you have those skills. There will also be a saw kerf thickness missing from each section. You could fill in with a thin spline, in a contrasting color or type of wood, OR just resand the circumference to blend them together again.

Plan C is to reuse just the cribbage board portion by sawing out away from the rest of the circle. Glue it up with a solid wood border on each side, rather than the plywood base.

Now this may sound strange, but I had a friend who did almost exactly the same thing with exactly the same warping condition. I saw kerfed the plywood base about every 6" and then made thin splines to insert in the kerfs after we had flattened it out with a little "over correction"
This was a Birds Eye Maple veneered table top with outstanding grain and it aws not to be cast away easily. So far I've not heard bad things about it in use, and I have seen it in person...drop dead gorgeous!

 

[Hammer1]

It's a guaranteed warp when you glue solid wood to plywood. The wood moves, the plywood doesn't. The same would happen if you attached plastic laminate to one face of the plywood. This effect is well known, now you know it.

 

[ryan50hrl]

So along with this topic....I recently built a router table top out of MDF.....laminated the top with Formica.....anyone think the same thing is going to happen with MDF?

 

[WillemJM]

1/8" is a little above my safety margin for veneer and movement. Looks as if the Oak lost a bit of moisture content and pulled the Ply. If you did the same thing on both sides, should be OK, but even then 1/8" is a bit of a risk.

 

[Steve Neul]

It might be worth a try to remove the finish from the underside and laminate some veneer to the underside the same thickness and clamp it slightly bent the opposite direction.

 

[dsabcan]

Thanks for all the input. I will definitely integrate some of the advise into my repair plan. I'll update the thread with the finals results.