Veneer Cracking on Curved Doors

      Advice on glue and substrate choices for preventing cracks in veneer applied to a curved flexible-plywood substrate. June 28, 2006

Question
I am relatively new to vacuum pressing and working with veneer. I am making some curved cabinet doors using ceylon satinwood veneer. I have created a good curved form and substrate of 2 ply, with 3/8" bending ply with a backer veneer sandwiched in between these at 90 degrees as usual, and am using Unibond 800 in this project. This is all good.

My problem is that I created a 2 ply of the satinwood glued to a backer veneer in a separate flat pressing with the backer running 90 degrees to the veneer, and when it came out of the bag, it gradually started to curl in the opposite direction of how I want to press it to the curved substrate. I sanded it well and glued it to the substrate in the bag and now I am starting to feel a fair amount of cracks along the grain under the bag. Any thoughts about this situation?

Forum Responses
(Veneer Forum)
From contributor J:
Your veneer is probably cracking for two reasons. First, the two-ply you've created is very brittle (largely a function of the Unibond's rigid glue line). Second, it's probably not bending evenly over its width.

If you have the luxury of starting over, I'd recommend laying your face up on 1/8" poplar bending plywood, which will distribute the bend better. PVA glue for the face veneer would probably also help. And try to get it sanded and back into the bag as quickly as possible, before things have a chance to start curling.

Also, you didn't mention what the radius you're bending is - is it very tight? By the way, two layers of 3/8" bending plywood will probably not yield a very rigid lamination. You might want to consider using six 1/8" lamina instead.



From the original questioner:
Thanks for your response. The radius is 18" on these doors. The one door I have made up (with the small cracks) seems quite rigid enough with the 2 plies of 3/8", so I feel pretty comfortable with this lay up. Because of budgetary constraints, I am going to have to try to work with the materials I have at the moment. I will try gluing up the 2 ply on the form to give the veneer a head start in the curve and try to do all the pressing in one day's time. If this doesn't work, then I will have to consider your advice as the next alternative.


From John Van Brussel, forum technical advisor:
You can blend up to 35% white glue with the urea glue, which will soften the glue line. This is what the membrane press industry had to do to get rid of the cracks when making raised panels.


From contributor D:
Bendable plywood is extremely unstable. You can expect veneer cracking as long as you use this product. A good solution is Econocore by Interior Products, Inc. 800-637-3539. They also sell kerfcore. Both of these will stand up to the task.

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