gorilla glue for veneering - update

[David Zaret]

today i finally got around to performing a test of using gorilla glue as a substitute for urea resin for veneering. i did a simple test of pommel sapele over MDF. i spread the gorilla glue very thin, using a credit card. i didn't wet anything - just put the glue right on the MDF. i applied a waxed laminate caul to test the adhesion, just to see if it would stick to the caul in regular practice. it was in the vacuum press at room temperature for about two hours.

the veneer certainly stuck - zero issues with adhesion, with foaming, or with coverage. BUT, the dreaded bleed-through was a major issue. the pommel sapele was effectively encased in plastic, with almost complete bleed through, despite my attempt to apply the glue in a very thin layer. maybe there's an approach to apply an even thinner layer, but i'm not sure what that would be.

so.... at least for the time being, i'm sticking with unibond. prior to this test, i did a large run of pommel sapele for some door panels, and with the unibond i could dial in the color, and the viscosity with the thickener to avoid almost all bleed through.

anyway, hopefully somebody finds this valuable. i had high hopes, but i fear it's not viable for veneering with "commercial veneers" (~0.025" thickness). with shop-sawn, or thicker veneers, i'm optimistic that polyurethane glue would work quite well. i might switch to it for door construction, where i use thicker veneers.

-- dz

[Jeff Roltgen]

Interesting. I too, got the itch to try polyurethane veneering, based on recent thread. Small 16x26" subwoofer face baffle.
- spread with plastic scrap in trowel fashion, then rolled with short-knap roller, only because I felt I was scraping more off than leaving in place and saw the roller in Mr. Thibedeau's article, and thought it may leave just the right amount. (1" MDF substrate)
- Super light mist of water on plain old flat-sawn, raw commercially-produced walnut veneer, which I'd taped face down on a veneering caul of melamine
- Vac press time roughly 90 minutes.

Results: ZERO bleed through, and a couple corners of the board did not adhere = just not enough glue.

How's that for a contrasting experience?

Not sure what to make of it. Hard to say no moisture added is the issue, as it seems that would just cause even more foaming, not reducing bleed-through. Hard to imagine the moisture acted as a deterrent to bleed through.
Certainly no instant convert to Polyurethane for veneering. I am likely to try again, just with more glue, but perhaps the species is the key difference to focus on in this comparison. Spread rates are so hard to judge/convey with words. One person's light coat is another's flood...

Jeff

[John TenEyck]

Interesting stuff, guys. I've only done a couple of panels so far with PU glue, using shop sawn veneer, and had no issues with bleed through. Never do, of course, except if there are cracks or worm holes, then it happens with any glue.

I'd suggest you start weighing the glue to figure out the required spread rate, just like you do (or should do) using Unibond 800. You can weigh the bottle before starting and then afterwards to see how much was used. After a few panels you'll be able to calculate the average used and then know how many gms/ft^2 are needed. With Unibond 800 it's 20 gms/ft^2 for me using a printer's roller to spread it. I suspect the optimum amount will be somewhat less with PU glue, but that will depend upon how you apply it.

John

[Kevin Jenness]

Sounds like marginally inadequate coverage and flatsawn veneer prevented bleedthrough while highly figured veneer with somewhat heavier (?) coverage had the opposite effect. The roller may have taken up enough glue in Jeff's panel to cause the loose corners. I wonder if varying viscosity due to age of glue had any effect. Further experiments using a thickness gauge to assess spread rate might be illuminating.

Jeff, how did the pu glue take to rolling? Would it work better with a non-absorbent roller like a printer's brayer?

Complete bleedthrough/saturation might be acceptable in some situations requiring grain filling, depending how the surface sands out and how the color is changed.

Thanks to both of you for reporting on your experiments. When you have an adhesive(s) that has proven to work it takes some motivation to try out something new and work out any kinks.

[David Zaret]

yeah guys i am almost sure it's the veneer i was using. a highly, highly figured, open grain pommel sapele. would flat sawn maple or walnut have had the same degree of bleed through? clearly not. alright, i'm not giving up yet... i'll learn from your experience, and find another way to spread it, and try again.

[Mike King]

yeah guys i am almost sure it's the veneer i was using. a highly, highly figured, open grain pommel sapele. would flat sawn maple or walnut have had the same degree of bleed through? clearly not. alright, i'm not giving up yet... i'll learn from your experience, and find another way to spread it, and try again.

Why not use Titebond Cold Press Veneer glue? PVA, water cleanup.

[David Zaret]

well, i don't love using PVA for veneering. first, the open time is pretty short. second, the water curls the veneers, which when i'm doing 20 panels, and need 20+ minutes to veneer and package everything, is an issue.

sometimes if i'm only doing a panel or two, i reach for PVA. but, for larger work, i've had better luck with urea resin (especially for the open time).

[David Zaret]

i think my concern about the gorilla glue bleed through was perhaps overblown.

i grabbed my sample, and sanded it. it sanded absolutely beautifully. the glue that bled through disappeared easily, revealing the veneer with excellent clarity, and opened up the grain. when i use tinted glues, sometimes the bleed through "stains" the veneer, and discolors it, even marginally. but this was beautiful. i sanded it all they way up and applied a finish, and it looked perfect.

i snapped a picture after 120 grit and a wipe-down.

i am going to reconsider gorilla glue as a veneering approach. the bleed through just wasn't an issue.

-- dz

485091

[Jeff Roltgen]

Jeff, how did the pu glue take to rolling?

I believe I would use it again. Troweling is not my usual method of spreading glue for veneering. Since I began with trowel and switched mid-stream, I'd say the roller may have picked up a bit more than it laid down at first. As usual, any fabric/fiber applicator needs to hit that sweet spot of ideal saturation before things really even out, and given small panel size, don't think the mini roller really had a chance to reach that point on this first go at it.

Mike: Cold press PVA is very frequently used in my shop. This was an experiment just to try the polyurethane glue.

Again, I am likely to make another attempt in the future, likely to stick with the roller method, and now that I know what too little looks like, I'll lay on a little more next time...
Hate to admit, but the ability to cheat my way out of a backer for smaller panels is really what motivated me most to try the polyurethane. It was a project for myself, so one can afford to take a chance and try something new.

[Kevin Jenness]

Hate to admit, but the ability to cheat my way out of a backer for smaller panels is really what motivated me most to try the polyurethane.

Are you hypothesizing that normal seasonal wood movement is not a big enough factor to cause cupping in small panels sans backer if using a non-shrinking adhesive?

[Jeff Roltgen]

Are you hypothesizing that normal seasonal wood movement is not a big enough factor to cause cupping in small panels sans backer if using a non-shrinking adhesive?

Not at all. It was a theory posited during a previous discussion about polyurethane glues, that the fact that no water is present in it, it will not cause the typical short-term warpage associated with water based glues, such as PVA's, right after the pressing stage. In that regard, I was interested in testing this theory, especially since, ironically, one has to introduce some moisture for proper adhesion...
It worked out that no appreciable warpage took place during the pressing/curing of the panel, so as a short-term test, that theory seems to have passed. I would theorize that, if I had done this with the normal cold-press glue I reach for, I would expect to see a bit of warpage, even considering the thicker substrate. This was the first time, and likely last, that I would do a layup without a backer.

To be clear, in no way am I implying that there is a glue out there that will allow us to dismiss seasonal wood movement. That's utterly preposterous. Only debate in this regard is whether any failure of glue line or cabinet structure will take place because of that layer of veneer's hygroscopic properties.

Again, this was a project constructed for myself, laid up on 1" MDF, so the "conditions" were favorable for this test. Wouldn't be trying out these brazen tests on a client's item. Turned out well enough that I finished the cabinet, and will now be able to observe directly if any long-term deterioration takes place.
Fortunately, the small loose areas got milled away, and even though that glue layer was apparently too thin, no loosening or bubbling took place when water-born topcoats were applied, so I'm not expecting any problems.

Instant convert to polyurethane glue for veneering? Not likely, but I now consider it one more option, instead of completely dismissing it for veneering as I was about to do just a few weeks ago.


jeff

[Kevin Jenness]

I would theorize that, if I had done this with the normal cold-press glue I reach for, I would expect to see a bit of warpage, even considering the thicker substrate.

jeff

For sure, and likely a permanent warp as the pva would set with moisture still in the panel. Many cabinets with fixed panels veneered only on one side have survived, but I too don't do that. Thanks for experimenting and reporting back. My biggest concern with pu glue would be shelf life, but I can see the possibility of using it for veneering in the future.