Lizard Coating?

most boatbuilding shops and boating supply stores have that stuff. when i built glass boats back in the day we called it "glass balls". the proper title is "inorganic microspheres". mixed with resin it makes a nice filler. mixed with paint; pretty much the same thing. don't confuse it with body type filler, it doesn't sand well but its pretty light and flows out nice.
got mine at West Marine and i'm mixing it with standard water based latex primer. it will go over the por15 i've already put down (fogged with spray bomb primer on top for adhesion), and i'll finish with B-quiet ultimate for sound deadening.