Thread: Strongest adhesive for veneer ?

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here is the mold with some veneer in it! I need the deck to be stiff as a rock after pressing it in a vice and PVA glue won’t do the trick !

Originally Posted by airapollo

Hi everyone !
i am looking to find the strongest most rigid glue for glueing 5 plies of veneer (0.6mm) together..

Urea Formaldehyde glue is perfect for that if you want rigidity - Michael Cooper used it extensively on his bent laminations using all manner of timber species.

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Originally Posted by airapollo

I’ve tried PVA wood glues but the deck turns out pretty weak !

This is a pretty general statement. Weak as in the glue bond between the veneers is not strong / well bonded and separates? or that the "deck" cracks easily when loaded / stressed?

"Thin" laminations of stacked thin veneers with the grain aligned in the one direction (unidirectional) will always be weak. However laminations of stacked veneers with the grain in alternating layers set at 90 degrees to the one below are very strong i.e. plywood.

I have done many projects involving laminations of veneers and have had plenty of success using PVA's, Polyurethane, Epoxy glues, at times forming quite tight radius bows without failure of the glue or assembly. In my teens and twenties we built triple diagonal laminate veneer 16' sailing skill hulls with all the frames being laminated assemblies. The strength in a "glue up" depends upon the "engineering" - how the laminates are aligned, how thick they are, how well the "composite" has been crafted (tight glue lines, no voids, etc), and the final cross section, and profile (2D or 3D) of the member. Most frames were unidirectional laminations of 3 mm veneers of northern silver ash and Australian red cedar typically 19 to 30 mm (3/4" to 1 1/14") thick, the hulls were 3 x 0.6 or 0.8 mm or sometimes 0.8/1.2/0.8 mm veneers.

Then there is a whole new world of laminations of wood veneers with man made materials - woven glass mat (uni or bias), kevlar etc. More on Laminating Wooden Beams - Epoxyworks

Techniglue epoxy with a 0.75mm spreader will work well. Polyurethane does work but if you don't have complete and even clamping pressure you may risk it bubbling up in sections. With something like a vacuum press it works well.

If it for a skateboard ( you mentioned deck) many people have success using titebond 111 if it is a skate board it is way too thin

Originally Posted by airapollo

here is the mold with some veneer in it..

I am going to go out on a limb (and hope that I dont offend) when i ask, what is your level of woodworking experience? Just so that we can all chime in as appropriately as possible.

Given the size of the mold and the small amount of glue you need, I would just stick with the suggestion of any titebond. It will be easy to clean up off that mold.

Polyurethane glue will be too expensive and you will never use it up before the bottle bad, unless you're making several hundred of these decks. Epoxy is also expensive, and the issue with Polyurethane and Epoxy especially, is that it will glue your mold together.

You can trust me on those latter statements because as an engineer I specialized in composites and tooling (basically we made race car parts and all the molds for it, a lot of which were milled from Aluminium), and our molds were buffed 3-4 times with mold release before each layup (glueup) - which was essentially Carnauba wax, so that the resins (mainly epoxy and polyester) didnt glue the whole thing together.



Kindest regards,
Siggy

Sorry PVA "will do the trick" hundreds of skateboards decks have glued with PVA, including three that I personally made. I can't speak for tiny little display models, exactly the same principle only smaller.

I'm wondering why the PVA didn't do the trick. How tight are you clamping it? It's possible you're getting a dry joint - too little glue. Or perhaps you'r using too much glue and/or uneven clamping. voids have no strength. What is the ambient temperature? Check the specs of the glue.
PVAs used to have a reputation for creep, but haven't heard that complaint recently. I used a PVA with catalyst about 20 years ago (sorry, can't remember the brand or number now) for load-bearing laminations in a chair and they haven't moved.

Originally Posted by airapollo

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here is the mold with some veneer in it! I need the deck to be stiff as a rock after pressing it in a vice and PVA glue won’t do the trick !

This post & image wasn't up when I started my reply this morning. Even though 0.6 mm veneers will bend to fairly tight radius bends asking 5 x 0.6 mm veneers to bend to that profile is pushing limits with the multiple reverse curves. The glue must act as a lubricant to allow the veneers to slip and conform to the former / mold. For the glue to act as a lubricant it must have a long "open time" or "working time" so look for a PVA glue with those properties.

The way I would approach the lamination is to,

1. use a lamination of 2 face veneers and 1 core veneer with their grain aligned to the longitudinal axis of the deck, and 2 core veneers with grain aligned normal to (90 degrees to) that axis.
2. lay out the 5 veneers in order and with the two face veneers with the "face side down." Mark the face sides with a pencil mark. The veneers must be steamed & bent in the correct orientation!
3. steam the 3 veneers (2 x face + 1 x core), then lay up without glue and insert into your former / mold. The veneers with grain normal to the axis do not need to be steamed as they will comply to the profile
4. clamp slowly to allow the veneers to slip, then let cool. IF they do not slip easily you may have to do each one separately.
5. check the "spring back" of the veneers to see how readily the steamed veneer/s comply to the former.
6. Do another dry assembly of all 5 veneers as a lay up without glue and insert into your former / mold.
7. clamp slowly to allow the veneers to slip, check progress. Remember you do not have the glue acting as a lubricant.
8. When satisfied with the prep work step up to a full assembly.
9. lay out the 5 veneers on a sheet of plastic or disposable work surface, in order and with the two face veneers with the "face side down." Check the mark on the face sides before glue up.
10. using a small foam brush / roller apply a generous coat of the PVA glue quickly to one side only of each veneer. Remember it has to act as a lubricant as well!
11. Stack the veneers in order and get into the press / former / mold ASAP.
12. clamp slowly to allow the veneers to slip, but don't take to long.
13. maintain constant pressure for the recommended clamp time in your ambient conditions, temp, humidity etc.

Hopefully you will have good success and can then streamline the process to see how far you can economize on the steps required in the process. Another thing to keep in mind is that all PVA glues are not the same. They are chemically tailored to specific applications, that require specific properties such as pH (acid / neutral / base - noticed how Tas Blackwood goes black with some PVA's or the PVA reacts with steel wool to produce black flecks); open time; "shear" i.e. viscosity / slipperyness; clamp time; even RF gluing to "instantly" cure the glue, etc and are manufactured as such.

The PVA (and other) glues we typically use as hobbyists have properties to suit "general applications." With some PVA glues shaking the bottle vigorously will change the "shear" or viscosity of the glue making it more "runny" which helps with projects such as yours.

As stated above I would also be using a mold release agent - but be mindful it has to be compatible with the finish/es you propose to use on the deck. Another tip - stick with veneers from wood/s that are recognized for their steam bending qualities.

Originally Posted by airapollo

Hi everyone !
i am looking to find the strongest most rigid glue for glueing 5 plies of veneer (0.6mm) together and pressing them in a mold .
I’ve tried PVA wood glues but the deck turns out pretty weak !
Any ideas would be greatly appreciated!
thank you !

PVA is no good for such applications (it's inheritantly flexible) if there is any sort of constant stress and or subjected to the outdoors... You need to use a resorsinol or epoxy glue.

Other glues such as UF109 (formaldehyde glue) are good but hard to find now.

You also need to make sure your press is well made so there is no voids when the veneers are pressed together. If not, you need to add a matrix such as very fine saw dust to strenthen the glue and add gap fulling properties.

And most importantly, don't cheap out. You need to see squeeze out so you know the project isn't suffering from glue starvation.

YMMV

Not correct used properly PVA such as Titebond lll will be fine hundreds of full size skateboards around the world have been constructed using Ttitebond lll

Originally Posted by The Spin Doctor

PVA is no good for such applications (it's inheritantly flexible) if there is any sort of constant stress and or subjected to the outdoors... You need to use a resorsinol or epoxy glue.

Considering that the former / mold fits in the palm of ones hand, and the resultant lamination is ~ 3 mm thick, I don't think the deck is going to be subjected to "constant stress" - not unless curious hands start testing how strong the mini-skateboard is.

I'm curious - why the minis?? Do you have adventurous guinea pigs / hamsters/ pet rats??

Urea formaldehyde or epoxy.

For the shape airapollo shows in his picture I’d use Urea Formaldehyde (cascamite, extramite, DAP plastic resin glue, Borden UF etc) or epoxy - as suggested by Riverbuilder and Siggyk. Very rigid bond, no springback. My choice would be UF - less messy than epoxy. Proper clamping pressure is essential. Not bagging PVAs, just my view on OP’s question re “most rigid” glues.

Best regards,

Brian