Well, it's doing it again - my 2' x 8' sheets of alder veneer (sticky back 3m) are curling cross grain, after staining and spraying with 2 coats of catalyzed vinyl sealer, followed by 2 coats of CV topcoat. These were thinned with approximately 25% butyl acetate.
The veneer is not glued to anything, it's just to be used for re-facing cabinets. So it's still in the 2' x 8' sheets. I had some curl back in Sept of '06, which turned out to be a nightmare, as after refacing the kitchen, the curling kept up its work and lifted the edges of the strips on the stiles and rails.
Now this time I happened to be watching for this curling, which took about 24 hours to start. So at least I have not applied the veneer in my customer's house yet. It's still in my shop. But what am I going to do to get this to stay flat? I don't dare use this. Why is finishing it causing it to curl? Refacing is done across the country on quite a large scale, so I know somebody has a solution.
From contributor C:
Take a piece of unbacked veneer and spray it with a coat of varnish and you will see the same thing happen. Or if you don't want to waste the varnish, just wipe some warm water on it and wait a few minutes - you will see the veneer curl. The reason is that you are wetting the surface, causing it to expand on one side of the veneer. As you will notice, it always curls with the length of the grain. As the finish dries, it usually relaxes to a degree. The answer to overcoming this problem is to use a veneer that is backed with phenolic, which is hard and won't allow it to curl to any degree that would be unsatisfactory. I have been using this since the 80's and have had no problems or callbacks. Oversize it by an inch or so, route off the excess, and file the edges just like laminate – job's done, collect your money.
My veneer is curling across the grain... That is, you could take the 2' x 8' piece and roll it so you have an 8' long tube. If you wet veneer with water, won't it expand the side you are wetting? My veneer is curling up toward the face concave. I will look into the phenolic back. My finish is solvent base, though, not water base. What do you use and what percentage do you thin it? For veneer?
Do me a favor and make a sample - spray two coats on one side, let dry overnight, and then spray two coats on the other side and let me know what happens. What should happen is that the coating thickness being equal on each side should lay the veneer back out again. I know the first time I used polyester on 1/4" plywood it happened, but as soon as I put it on the other side, it laid back out flat again, as all other pieces I have done since then.
Also, do not use water base, continue with the solvent base - you've misread my first post! All I wanted you to do was put water on a sample to show you how it curled, not knowing yours was an applied finish problem. My mistake.
Comment from contributor W:
If you glue the veneer down with water based contact cement (professional quality available at laminate suppliers) you won’t have a problem with it curling up. The gas based sealers and top coats you are using are leeching through the veneer and compromising the glue you are using. They will not affect water based contact.