How to Paint on Casting resin Model Pro, Fabricast 50, Color Pro and Toughcast. If you rather brush on and use your choice of paint. Make sure you follow the steps up to the primer. Primer is sprayed on, goes on like paint dries matte. Allowing a barrier that can improve the paint adhesion and finish will look smoother. Let it dry overnight you can even sand the primer lightly of course. Then apply your choice of paintbrush on or spray paint.