I recently had a stone countertop installed with a mitered edge. For support, the installer put plywood under the stone. However, because the slab wasn't flat on the underside (to my surprise) - the plywood is sticking out in places about 3/16".
Additionally, the plywood he used wasn't big enough so it has a couple of pieces screwed into it to make it "flat" (obviously provides little support).
Sidenote: The slab is also supported by metal brackets, not just plywood.
I want to make the underside of the countertop smooth and need help with finding the best way to do that.
I was thinking I can remove the screws then use a planner to shave down the plywood, then use Bondo wood filler to make it flat, then sand and paint it.
Or I could use a belt sander instead of a planner.
Any other, easier, ways to accomplish this?