Veneer Adhesion Failure

[Ken Krawford]

I glued some 20" x 27" unbacked cherry veneer with Titebond Coldpress Veneer glue. In spite of using every clamp in my shop and 5 cauls I still ended up with a couple of areas where the veneer didn't adhere to the substrate. The one other time this happened I tried injecting some glue into the void and then clamping but the results weren't good. I don't know if ironing the areas would melt the glue or not. The veneer was applied yesterday and Titebond says to allow about 72 hrs for full cure.
Does anyone have any experience with this product regarding using heat to melt it? Any other suggestions would also be appreciated.

[Mike Henderson]

I have not had good success with the Titebond coldpress glue. As for re-gluing areas that didn't stick, use Gorilla glue (the poly stuff, not the PVA stuff). The problem with injecting PVA type glues is that PVA doesn't stick well to cured PVA.

Mike

The way to inject Gorilla glue under the veneer is to cut the veneer along the grain and then use something to carefully lift the veneer. Work the gorilla glue under the veneer with a thin rule - one of those pocket rules that you occasionally get free. Try to work the glue under the veneer on both sides of your cut. Then put a caul with packing tape on it, or put a layer of plastic under your caul, and clamp it. One problem you can run into is that the glue builds up a bit so you can have a small bump there. You can usually sand it down.

[One other comment: When applying the glue, make sure the substrate is clean. If you have any questions, run a sander over it to take the top layer off. Only apply glue to the substrate, not to the veneer. How much to apply is by experience - too much and you'll get a puddle of glue in spots and it will look like the veneer didn't adhere - too little and you'll have spots that didn't adhere. You need to apply the Goldilocks amount.]

[Kevin Jenness]

The problem is likely uneven pressure, insufficient glue spread or a contaminated substrate. If you plan on doing much veneer in the future a vacuum press is a good investment and will give consistent pressure.

As far as heating and re-pressing it, it's worth a try- what's the worst that can happen? Heat the area with an iron over a damp cloth to prevent scorching and rub it down with a wood block with an eased edge while still hot. If that fails you can try injecting polyurethane or cyanoacrylate and clamping. You can force the glue into the depths of the bubble with compressed air. Once the new glue has set, dampen the surface with a wet rag to see if the problem is solved.

[Phil Mueller]

I’m sorry to hear about the failed glue up. I have successfully used Titebond cold press for dozens of projects and have never had a failure. I’ve done some with cauls/clamps and some with a vacuum press. Never an issue.

I think Kevin is right about what may have caused it. Or as Mike suggests, too much glue and it’s actually a hump.

By the way, I rarely leave it clamped up more than a couple of hours.

[Jerry Wright]

I have used cold press glue many times with no issued. I keep matching pieces of BB plywood and trap the panel between them. I have some deep throat(6-8") clamps and clamp toward the center first, then around edges. I also have a pair of parallel clamps (woodcraft) that work on wider pieces.I place wax paper between the BB and the veneer so there is no adhesion. I find this glue to be amazingly good. I would use a hot iron on your "bubbles" and see what happens.

[roger wiegand]

I don't know about coldpress, but with regular titebond ironing it flat is very successful. It reactivates with heat and bonds very strongly. I often use it as my first choice application method-- titebond on both the veneer and substrate, let it dry, and then iron them together to bond.

[Mel Fulks]

I’m surprised that no one is using hot hide glue and veneer “hammer” Certainly much faster than clamping, except when pieces of the same
size can be stacked.

[Mike Henderson]

My problem with hot hide glue for veneer is that hide glue is water based. Some veneers expand a fair amount when they get wet. With certain veneers it's a problem to lay with any water based glue, such as PVA, and get it laid and in press before the veneer absorbs much water.

A particularly difficult pattern to lay is a radial match in a rotary cut veneer, such as rotary cut bubinga (often called kewazinga). Burls can also be a problem. As soon as the bubinga absorbs any moisture, it expands so by the time you lay all of the pieces except one, that one has to be smaller than the others and can be noticeable.

I've had to use a non-moisture based glue for certain veneers in certain patterns. For example, I did a table top in a radial pattern (could have been 16 pieces) in kewazinga. I used epoxy. It came out very nice.

But our ancestors laid burls in rotary patterns (sunburst) with hot hide glue so I assume there's a way to do it and make it come our properly.

Mike

Attachment 456637

[Mel Fulks]

Mike, thanks for that explanation. I remember when white glue was quickly accepted by shop owners who had used hot hide glue for years.
They were tired of the cost of glue pots , as some did get knocked over and broken. Then they found that white glue would creep and make
perfectly flat veneer pieces move and have to be rescraped and sanded , and it took more time to set. Modern glues can block stain, so that can be a time killer when a finisher finds that and has to send the piece back to the cabinetmaker. The thinking was that getting one man to
fix a problem made by another increased the number of faults.

[Ken Krawford]

Thanks everyone (and especially Mike for the detailed response). I glued up a "test piece" yesterday after posting and left an area in the center without glue. I'm going to use that as a practice piece before proceeding.
Mike, is this the Gorilla product you recommend - https://www.gorillatough.com/product...gorilla-glue/? I'm afraid it is and it's one product I hate working with for a variety of reasons but will use it if it's the best solution for my problem.

[Jim Becker]

I agree with the comment above about uneven pressure. Using a vacuum press as suggested is one solution. You can also use a full size piece of material on top of the workpiece to "make a sandwich" so that clamping pressure can be better spread...that works with both "a gazillion clamps" as well as with a vacuum press. I actually keep some MDF panels for doing small laminations in my vacuum bag that are scored to permit better air extraction while going under vacuum for this purpose.

[Phil Mueller]

Jim, I have a variety of sized mdf and plywood panel cauls as well, with the corners rounded to protect the vacuum bag. I also have a few that have thin felt covering the surface. I use these when I’ve put together a veneer piece that includes inlay that sits a bit proud of the veneer. The felt helps to provide even pressure to both the proud inlay and the surrounding veneer.

[Mike Henderson]

Thanks everyone (and especially Mike for the detailed response). I glued up a "test piece" yesterday after posting and left an area in the center without glue. I'm going to use that as a practice piece before proceeding.
Mike, is this the Gorilla product you recommend - https://www.gorillatough.com/product...gorilla-glue/? I'm afraid it is and it's one product I hate working with for a variety of reasons but will use it if it's the best solution for my problem.

Yep, that's the stuff. I don't use it for anything except fixing veneer, probably for the same reasons you hate it. I buy the smallest bottle they make and it gets hard in the bottle before I use all of it.

Mike

[Mike Henderson]

I agree with the comment above about uneven pressure. Using a vacuum press as suggested is one solution. You can also use a full size piece of material on top of the workpiece to "make a sandwich" so that clamping pressure can be better spread...that works with both "a gazillion clamps" as well as with a vacuum press. I actually keep some MDF panels for doing small laminations in my vacuum bag that are scored to permit better air extraction while going under vacuum for this purpose.

Jim brings up an important point - you really should use a caul when pressing veneer. When using a vacuum bag, you have a bottom platen which works as the bottom caul. But you need to make a top caul that generally fits the work (just a little bit larger) and round over the top edges so it's easy on the bag. The problem is that you do work in all different sizes so you wind up with a lot of upper cauls in the shop. I keep saying that I should use some of them for scrap work but I keep them around "just in case" I have something that exact size.

You can't use a caul that's too big because the vacuum bag will pull the sides down and generally release the pressure in the center of the caul. The reason for making it a bit larger is for convenience of getting it aligned on the work in the bag. If it's "exactly" the same size as the work, you have to align the caul very accurately and even then it can move as the vacuum is pulled. So I make it maybe a !/4 inch larger on each side.

Whatever you do, make sure you put plastic between the work and the caul. Glue can come through veneer and if it does, and you don't use plastic, it will glue the caul to the veneer. Removing the caul will probably damage the work.

Mike

[Mike Henderson]

Jim, I have a variety of sized mdf and plywood panel cauls as well, with the corners rounded to protect the vacuum bag. I also have a few that have thin felt covering the surface. I use these when I’ve put together a veneer piece that includes inlay that sits a bit proud of the veneer. The felt helps to provide even pressure to both the proud inlay and the surrounding veneer.

Phil makes a good suggestion. I do the same but I have some heavy canvas that I use to spread the pressure, or sheet cork (I bought a large roll of it years ago).

Mike