A few tips for flat paint. 1. Acrylic sanding blocks for body filler, primer, and clear coat. 2. Cut the polyester primer completely flat with a long acrylic block, and either 80 or 100 grit. 3. Cut the clear coat completely flat with an acrylic block and 600 grit. No 'flow coats' either! The less you spray anything on, the less you have to cut flat.