Balancing Veneered Panels

Even small veneered lay-ups require back-veneering to prevent curling. But with care, you can get away with using a different and less expensive material for the back side. July 13, 2006

Question
I was wondering if it is necessary to apply veneer to the back side of a panel when using 18mm fin-ply Baltic birch as a substrate. I'm using 10mil backed veneer. The parts are relatively small, 36" long max. Will my panels be unbalanced if I just leave the backside alone?

Forum Responses
(Veneer Forum)
From contributor A:
It doesn’t really matter what the substrate is. If you don’t veneer both sides, the panel will get pulled hollow by the unbalance. Someone could have a special situation where the panel was going to be glued to something very rigid and would be held straight.


From the original questioner:
Do you think that Baltic fin-ply would be less likely to buckle than say MDF, composite core or even standard plywood? Also, if the parts were cut oversized prior to laying-up and then cut to finished size would this help? I'm guessing that the larger the panel, the more unstable it will become, if only veneered one side.

From contributor A:
I buy the highest grade of Baltic birch they sell, and it is rarely ever flat when I get it. It’s hard to say if it would be pulled hollow to a lesser extent than MDF. It would make sense in theory that the stiffer the material, the less it would bow, but wood products can be contrary sometimes.

I don’t see any chance of making the part over size cutting down on bowing. It is however a standard practice to make them oversize before pressing. The extent that a part will bow is relative to its dimensions. I don’t understand your resistance to veneering both sides though. If the veneer is a really precious or rare wood you can use a veneer of lesser value on the flip side. It is only a rule of thumb that both sides must be the same species.



From the original questioner:
I'm pressing some quartered zebrawood and I didn't want to waste it on the back side of drawer fronts. Do you know of a good alternative to balance out the zebrawood?

From contributor A:
For the back of a drawer front, I would use anything I had around that was the same thickness.

From contributor B:
Do you have to balance panels if you are using PSA veneer? I am building a small television/component stand, and will be using MDF as a substrate. I would like to use PSA laminate for the exposed faces. If required, are there any PSA backing quality veneers?

From contributor C:
Regarding balancing, the proper method is to use the same veneer and the same cut - plain slices, riff cut, etc. - on both sides. For example, the P/S cut will curl and the R/C will stay flatter. You do not want unequal pull on the opposing sides. The MC must be the same on both sides.

We make every effort to do this but there are many situations that just do not work out – for example, expensive materials and the need to use off cuts as available. The balance is most critical on thinner panels, less than 1" core. For 1" and above I'm less concerned with making a compromise.

You should have a good idea of the pull each wood has. It's ok to use Ash and cherry, but using maple and Anigre would not be so good. Often the problems do not show up until you build or even deliver the product. Another problem is that people do not let the panel completely dry before working with it. It takes many days in a 70 degree room to fully acclimate panels using PVA glue. They must be dead stacked for the entire time. UF glue is faster when hot pressing, but the same when using the water/powder product.

Many people on this forum seem to be doing small projects. I would suggest that the same on both sides should be the rule on any hand made high quality work. Ask your supplier for reject grade material, even burls etc. They often want to get rid of it. When it's all said and done, what is $20 worth of veneer on a major work?

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