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Veneer "bubble"

5/6/20       
Daniel Member

Hi All,

Any thoughts on the cause of the attached photo. Paper backed red oak veneer overlay'd on 45lb particle board core with 5" solid hemlock "cap" 1-3/4" thick. Cross banded PVA glue used in a hot press. It appears there is some bubbling happening just on the hemlock blocking and not on the particle board core.


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5/6/20       #2: Veneer "bubble" ...
Tom Gardiner

I'm not familiar with hemlock in the shop but is it possible that there is a large pitch or sap pockets? The hot pressing could flow the sap to the surface.
Just curious, why such a large piece of solid?

5/6/20       #3: Veneer "bubble" ...
rich c.

I hate paper backed. You can get a good result with the adhesive on the base and the paper, but then get a release between the paper and veneer just because of solvent leaching through the veneer. What kind of finish schedule? Two wood ply veneer is far superior to paperbacked if you must buy the veneer already laid up.

5/7/20       #4: Veneer "bubble" ...
Daniel Member

Tom Gardiner: The reason for the large solid block is for a face mount door closer, this is typical in 20 minute fire rated suit entry doors. We have never had any issues with hemlock in any other laminating processes but that is a good thought. The odd thing is these doors have the same block on the bottom of the door and it appears its not happening there. Id expect it more on the bottom because its plowed out for an automatic door bottom sweep.

5/7/20       #5: Veneer "bubble" ...
Daniel Member

Thank you for the thoughts and replies.

rich c. : I am asking the finishers for their schedule, I believe it was a lacquer based spray stain with clear over. This was my initial thought but then there are no signs of this happening anywhere else on the door but the top block. The same solid block was used on the bottom and also no delamination/bubbling anywhere thats PB core. It appears the only bubbling is on the top block.

5/7/20       #6: Veneer "bubble" ...
Tom Gardiner

Now that the veneer is ruined put on your deer stalker hat (Sherlock Holmes) and remove the veneer to see if you can determine the cause of the fault. And of course get back to us when you do.
Your photo shows the top block seam telegraphing through the veneer as well. This would be improved with a cross banded veneer as well. Probably more than double the price of paper backed though.
I don't think it would be finish solvent causing the bubbles. A cross linked PVA is not that susceptible to solvents.

5/7/20       #7: Veneer "bubble" ...
rich c.

If it was a hemlock problem, why aren't there bubbles all over that entire board?Looking at it a little closer, looks like a section of rift grain where the bubbles are located. I'm sticking with a solvent issue as it could wick deeper in the rift grain section.

5/8/20       #8: Veneer "bubble" ...
ThomasFR

99% guarantee paper backer bond to veneer failed. 50 years of furniture restoration & finishing here. Solvent penetatration unlikely. Quality control issue with veneer manufacturer is most likely cause.

5/8/20       #9: Veneer "bubble" ...
John S

I agree with ThomasFR, extremely likely it's a bond failure between the veneer and paper. Having been involved in commercial door manufacturing for 40+ years, I would never recommend anything but a 2-ply door skin (veneer + HDF backer) in any commercial door application. That would solve all of your issues.

5/9/20       #10: Veneer "bubble" ...
BH Davis  Member

Website: http://www.bhdavis.net

Have you tried knife slitting one of the larger bubbles and peeling it back a bit? You might be able to determine if it was veneer to paper or paper to wood failure.

And although likely not to be successful you could always try to do a repair this way by easing in some adhesive once a bubble is opened up. Or with a syringe inserted into a bubble and then press rolling with a J-roller.

BH Davis

2/23/22       #11: Veneer "bubble" ...
Connor Johnson

Looking at it a little closer, looks like a section of rift grain where the bubbles are located. I'm sticking with a solvent issue as it could wick deeper in the rift grain section.


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