I'm getting ready to build some cabinets and book cases from birch plywood. I'll be painting them white. One suggestion I heard from a coworker is to brush a thin layer of urethane on the bare plywood and then sand it before priming and painting. This is supposed to keep those little wood fibers from sticking up through the paint. Has anyone done this before? Sound like a decent idea? I was sort of afraid of the paint not adhering but I guess if it's a thin coat it'll soak in pretty well and then get sanded.