PUR adhesives

      A Q&A on PUR hot melt formulations and their proper use. December 6, 2000

I understand that Jetweld is not a hot melt but a warm applied moisture-curing urethane. Does that mean that if it is subjected to heat it does not re-soften?

Also, there is a specific formulation (TE-100) that is thin viscosity and forms a thin glue line. Is the glue line thinner than, similar to, or thicker than yellow glue?

Forum Responses
Your understanding is accurate. PUR hot melts are just that, PURs which are applied as a hot melt. Because a chemical reaction occurs in the curing process, once cured, they are irreversible. This doesn't necessarily mean they are heat proof. It does mean that they have much higher resistance to heat than a normal EVA hot melt.

Regarding the glue line, I'd have to say that there are no formulas currently available that can give you a glue line as thin as PVA (yellow glue). I usually tell people that these kind of adhesives are excellent in a wide range of applications but if you're looking for a quicker way to produce panels, it's not the right glue.

Jeff Pitcher, forum technical advisor

From the original questioner:
I am not considering edge gluing boards. I do want to glue beveled mitered plywood. I need a perfect seam. I was going to use the vgroover system of tape and glue.

If you’re using a closed cell hardwood plywood, like birch or maple, you may find a wicking cyanoacrylate will give you a perfect, fast and easy joint. Wicking is different in that you must add it after the joint is clamped. It sets in minutes. It may effect staining.

From the original questioner:
The “it may effect staining” part is a show stopper.

Any adhesive you choose will affect staining. There are some PUR hot melt formulations that are thin enough to produce an excellent glue line in a mitered joint. The trick is to apply considerable pressure quickly.

There are a number of PUR hot melts available. Most companies are interested in selling bulk but 3M, Seaco, and Jowat are involved in selling the smaller 10 oz cartridges. Seaco has the greatest number of formulations.

Jeff Pitcher, forum technical advisor

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