DAY TWO -- Sanding primer and adding color/clear coats
After letting the primer surface to dry overnight, you are ready to sand the surface in preparation for the color coat.
Using the 400 GRIT sandpaper sand the primer coat using the criss cross method again. This step is very important in that you sand using moderate but even pressure. You want to sand to a dull smooth surface. Make sure there are no imperfections on the surface [divots, deep scratches, etc.] as these will amplify when applying the color coat. After getting a smooth sanded surface, apply and repeat the sanding process with the 600 GRIT sandpaper using the same criss cross method.
This will leave a super smooth surface ready for the color coat.