Bonding Plastic Laminate to Apple Plywood

      Thoughts on glue choices for adhering PLAM to plywood. May 5, 2007

Question
We are about to build some plastic laminate doors on a 3/4 inch appleply (similar to Baltic birch) plywood core. The reasoning behind the plywood core is that the customer would like to see the striations from the plywood core on the edges of the doors. We like the idea because there isn't a whole lot of edgework to produce. Our goal is to keep the door as flat and straight as possible.

We are contemplating laying the long grain of the PLAM perpendicular to the long grain of the plywood. Our thinking is that this would help balance the panel. We are planning to use a vacuum bag for bonding the glue and are planning on using either an aliphatic type yellow glue or a hard plastic marine resin type glue. Which type of glue would be best for this? Cycle time in the bag is not important to us, but flatness is.

Forum Responses
(Adhesives Froum)
From contributor J:
We've had good results doing this with just about every type of glue; I did recently notice that Formica brand recommends PVAc (at least for ColorCore, which is what we were using).

All that said, it makes sense to me to take water out of the equation (remember, you're covering the panel with plastic - how/when does the moisture escape?) so my preferred adhesive is Unibond 800 (two-part urea formaldehyde) from Vacuum Pressing Systems.

The other thing you have to deal with is the flatness of the appleply - will it be flat enough for your application?



From the original questioner:
Good point about the moisture migration. I hadn't thought about that. My reasoning for the plastic resin glue was that it might be stiffer than yellow glue. I figured that if I vacuumed the blank to a flat basis, it might stay that way. The only urea glue I have ever worked with is a water/powder marine resin glue by Weldwood. This stuff is brown and takes about 24 hours to fully set up. Do you know anything about this type of glue? Might it be appropriate?


From Jeff Pitcher, forum technical advisor:
It sounds like we need some clarification here. Your instincts are right for this project. The resin you mentioned would work well for you in a vacuum bag. A PVA would also work well. The powdered resin you referred to is basically the same as Unibond 800. Both are urea formaldehyde resins. Once you add the water to the powder or the catalyst to the resin, you have essentially the same thing. A lot of folks mistakenly assume that there is no moisture issue if they use something like Unibond 800 for their project. The fact is that liquid urea resin is about 50% water. So, no matter which resin combination you use, you are adding about the same amount of water to the mix. Regardless of your adhesive choice, the moisture will find its way out through the process of evaporation. My advice (considering that you have no time constraints) would be to go with a UF resin.


From contributor J:
Thanks for the clarification; I didn't realize that Unibond had that much water in it. I have a related question now: Where does that water go when we leave catalyzed UB out in a container? It seems like the mixed adhesive sets up much faster than water could evaporate out of it and there's no precipitated water. What's going on in there?


To the original questioner: I would assume you are doing both sides at the same time? As long as both sides of doors are glued up on a flat surface at the same time with the uf, it shouldn't be a problem, as uf does not creep.


From contributor E:
Make sure you laminate both sides of the door. It wasn't clear if you are doing this. If not, you will get a warped door. The laminated side will pull the plywood in the direction of the lamination.

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