Darryl Keil
Posts: 1455
Joined: 2003-05-22
Location: Maine
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Scott,
Your words truly warm my heart. So much of what you say is exactly what I preach. Or should I say, with me, you're preaching to the choir. Urea glue is superior for veneering, for all the reasons you site.
With that said people are going to use white and yellow glue for the reasons they do. I prefer to let people know what I think is best and then support folks the best I can in their choices, as long as people aren't using contact cement, that's just over the line for me. If yellow glue is used carefully and in less critical situations it will of course work. As good as a urea resin glue? No, but acceptable.
As far as not drying in a vacuum press this is of course true. Well partly. There are really two phases to the use of all PVA glues, the bond phase and the cure phase. The bond phase requires no water evaporation, the cure phase does. During the bond phase water is drawn into the substrate and veneer through capillary action and pressure, the glue is dragged in following the water so to speak. When a sufficient amount of this has taken place you get the bond phase. This is why when you glue solid boards together you can take them out of the clamps in ten minutes or so. Nothing has dried in the joint within this time, you just have the bond phase. The cure phase comes when all water has left the materials being glued. The rule is you don't work a panel until the cure phase has completed.
Now with veneer this is trickier because you have so little surface to draw the moisture away from the glue line. With solid wood you have so much more surface to work with and all the excess glue is driven out of the glue joint as well. With veneer you cant expect excess glue to be drive to the edge of a panel 2' wide. With veneer you have to be much more exacting with the amount of glue you apply if you're going to get a good bond phase.
This is why I was asking Alec whether he used paper backed or raw veneer and what species. Obviously raw veneer has more surface to absorb the glue than paper backed does. Some species absorb better than others as well. Would cold press glue have worked better? Not really, as it still has the same required bond phase as any other PVA glue does, at least for the most part. Would Alec have had this problem if he had used a urea glue? Highly unlikely. Urea's don't have a bond phase only a cure phase which doesn't require moisture removal from the glue line to complete the catalyzation process. You don't need to be as precise with the amount of glue you use either. The answer to using PVA glues for veneer is using more precision with the amount of glue applied.
Now, I could have just said don't use a PVA glue, use a urea and you wont have this problem in the future, period. Believe me, Ive said it before countless times.
I prefer to take a softer approach these days. Tell folks what I think is best, let them make their own choices, and support folks the best I can.
Hope this clarifies things, and please, keep right on doing it exactly the way you are.
Sincerely
Darryl Keil
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