Curling Problem with Peel-and-Stick Veneer

      Pros suggest solutions to a problem with veneer that curls as it dries after finish is applied. August 14, 2007

Question
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 that turned out to be a nightmare, as after re-facing the kitchen, the curling kept up its work and lifted the edges of the strips on the stiles and rails.

This time I happened to be watching for this curling, which took about 24 hours to start after the last topcoat. So at least I have not applied the veneer in my customer's house yet; it's still in my shop. What can I do to get this to stay flat? I don't dare use this curled this way. Why is finishing it causing it to curl? Re-facing is done across the country on quite a large scale, so I know somebody has a solution.

Again, the curl is not with the length of the grain, it is across the grain. The veneer will be cut into strips and to length and applied with a waterbased contact cement to the cabinets in my customer's home. The last time I used veneer that had curled after it was sprayed, I rolled it out flat after gluing and applying, but the strength of the curling just gradually lifted the edges over a month's time, and I had to redo the whole kitchen. I'm not going through that again. The second time around the veneer behaved, was nice and flat even after the finished was sprayed. That was in late January. I really need to find out the cause of this. I'm supposed to start install on Monday.

Forum Responses
(Cabinetmaking Forum)
From contributor M:
I've run into this problem but solved it by not using peel and stick veneer. That veneer is quite thick and has a mind of its own.

I buy the cheaper 10 mil paper-backed veneer, spray contact cement onto the paper, and stick it onto a sheet of cheap 1/8" MDF while the contact cement is still tacky (I don't put any glue on the MDF).

Then I go ahead and stain and finish the veneer while it is on the MDF, and cut the finished panels into the appropriate width strips for my re-facing job. When I am on the job, I use a miter saw to cut the strips to length to fit the cabinet faces, peel the veneer off the 1/8" MDF, and apply it to the cabinets. For the finished ends, I precut the pieces oversize in the shop, again peeling off the veneer to apply.



From the original questioner:
Thanks for the response. Do you reapply glue to the back of the veneer after peeling off the MDF? Do you put glue on the cabinet faces? And what led you to gluing on the MDF? Does the paper backed veneer curl also after finishing unless it is on the MDF?


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From contributor C:
I've never used any sticky back veneers, but I have had some experience with curling veneers. I have found that heavily or well lacquered veneer faces must be sealed and sanded on the backs or they will curl in the first 24 hours. The contact cement works well on a smooth, sealed surface. Trim carefully. Seal edges after smoothing.


From contributor P:
Isn't this caused by the finish shrinking?


From the original questioner:
Unfortunately, I can't spray the sticky back veneer, but you do have a point. We all spray our doors and panels equally both sides to stop warp.

Contributor P, that's what I am wondering. And since I have one sheet of the sticky back left and no regular veneer, I'm going to stain it and try reducing the thinner back to 15% as I was using 25% for better flow. Does the extra thinner, when it evaporates, allow the film to shrink too much?



From contributor M:
You spray contact cement on the paper back of the entire sheet and stick it on the MDF while it is still tacky. Roll it down hard and it should stick quite well, but will peel off easily later. Then stain and finish the face of the veneer. This will be easier to do with the veneer stuck to the MDF, and curling should not happen to any great degree because you have temporarily stiffened and sealed the back of the veneer with the MDF.

After you have stained and finished the face of the veneer as a whole sheet on the MDF, you can cut it into strips for your re-facing job while it is still on the MDF and then peel off the veneer from the MDF on the job. The MDF keeps the contact cement fresh so it still sticks well to itself (at least with the contact cement I use). If it has somehow over-dried, you can usually refresh it by going over it with a rag damp with lacquer thinner. You can then apply the veneer to the cabinets you are refacing after you have applied contact cement to them as well.

I believe that the veneer curling problem you have presently is due to a humidity change, not to finish shrinking. From your photo, it doesn't look like the veneer is curled so much that it will not stay flat with contact cement holding it down. How are you going to cut it into strips? A straight edge and razor blade will work if it is too curled for a table saw.



From the original questioner:
Are you using conversion varnish? This stuff cures very hard. And if the veneer is curled when it cures harder and harder as time goes by, you cannot flatten it without cracking the veneer. I am going to clamp it flat till it cures and see what that does. I have thought it might be humidity, but why does it curl only after about 24 hours after the last coat? I know it is dry in Arizona and wood will cup to the top side when it dries. I currently use a veneer/laminate slitter hand held to strip the veneer on the jobsite, then cut with a paper cutter to length.


From contributor M:
I use either conversion varnish or lacquer, depending if the veneer will ultimately be exposed to water or not (like being below a sink). I have never had veneer warp as quickly as you say. That's why I think it's not the finish tension that is doing it. The dryness of Arizona weather would cause the most permeable face of your veneer to dry out quickest and to slightly shrink, causing that face to cup. That would be consistent with the direction of warp you show in your photo.

The back side of peel and stick veneer is completely sealed by the peel off liner and thus won't allow drying from that side. With paperbacked veneer, both the wood face and the paper face suck in or lose moisture together (that is, if one face is not laying flat on something which prevents the process). I think that the paperbacked veneer is also thinner so it is more flexible even if it is warped.



From Professor Gene Wengert, forum technical advisor:
Put a little finish (maybe just the top coat) on the sticky side of the veneer and see if it dissolves the adhesive. If so, the solvent in the adhesive is softening/dissolving the adhesive.

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