We are preparing a kitchen counter top for new formica. The original plywood is still intact but is rough, so we will glue 3/8" plywood on top of it for a smooth durable surface. What is the best glue to use to bond these two layers of plywood together, given they will be the substrate for the formica?
I don't think it's going to be critical but when in doubt: PL. As far as I can tell, PL Premium can bond anything to anything. In a case like this, do a bead around the perimeter and bolts (quarter sized blobs) about 8" inches apart in a grid and you'd have to sacrifice a goat to a powerful deity to get those two pieces of plywood apart. The more important bond to consider is the laminate to your substrate. On that topic, counter tops are made with particle board, not plywood. PB is cheaper, flatter, and free of voids. Go particle board if you can (yes they make it in 3/8"), if not don't worry just make sure your plywood is of very high quality.