How I do I prep an existing, painted fiber glass for for a new coat of paint?

To prep an existing fiberglass door that has a coat of paint on it:

1. Scrub clean with soapy water and a nylon scrub brush.
2. Scuff with a gray or maroon synthetic steel wool.
3. Rinse.
4. Primer needed is not needed if you are using General Finishes Milk Paint unless you are switching to a lighter color. You could prime with Linen or Seagull Gray Milkpaint, or there are several brands of exterior primers available, such as Kilz All-Purpose Primer. Be sure to let other brands of primers dry overnight. When you cross brands, extended dry times are always best practice.
5. Apply 2- 3 coats Milk Paint.
6. Exterior 450 Topcoat is optional. Do not apply a topcoat over white or light paints as it may cause yellowing. General Finishes Milk Paint is self-sealing and does not require a topcoat.