George, If ya trying to get it as flat as possible cause its a lumpy or un-even substrate after grinding the old stuff glass. Id use vinylester duratec (if your going to ues vinylester resin) to skin coat the low spots to save some work and time, or skin coat the whole area. But personally, I dont have a problem with grinding something down thats 10 or 20 yrs old and flat with 32 grit and wiping it super clean with acetone and the laying it up with vinylester or any resin without having any bonding issues. The acetone softens it up and will help it bond , so use generously just before you start. And back wet the prepared substrate before you add the glass. Be heavy handed with the resin on the 1st layer and then let the 2nd layer pick up any excess right behind the 1st..........
...... Make sure you use vinylester catalyst.