My painter and I discussed using white sealer and decided not to do it. He lets his sealer cure, then wet sands it prior to paint to level it perfectly. He says if you don't do that you'll see it in the final basecoat (he's really picky). We decided to spray a white base before spraying the orange instead. It's thin, doesn't orange peel, and makes everything the same color.....and it's pretty cheap.