Expanding Glueline


From original questioner:

I am working with medium density concrete form overlays. Our glueline usually bonds fantastically to plywood but recently one of our customers has started buying cheaper plywood with more irregularities in the surface. This is causing problems with bonding.

I'm wondering if anyone has any ideas about how to get a glue or glueline to expand under heat and pressure? (approximately 285F and 220 PSI, these panels are pressed onto the plywood)

Our glueline is made with a phenol/formaldehyde resin if that helps. I've tried using an isocyanate compound(like gorilla glue) with a blocker that releases at press temp but I believe it needed water to expand.

Currently I'm waiting for some potassium bicarbonate to incorporate. Any suggestions? Thanks!

From contributor Je

Just a thought, but have you tried adding a filler to your phenol/formaldehyde? We've had some good luck using shell flour in similar situations.

From contributor Tr

Thanks for the great suggestion! We actually use a similar filler in our mix. I've tried different fillers and some of the thicker ones give us a thicker glueline that can produce the effect of an expanding glueline, but the extra glue bleeds through the overlay.

I'm considering altering the overlay in order to handle a glueline with a thicker filler (and therefore thicker coat) but that would require altering the glue as well as the overlay, which complicates things.