I found the email from Krylon. I was asking about using Fusion as a primer or undercoat...
The Krylon Fusion Paint may be used as a primer, however it was not manufactured nor tested as such. I would recommend using the Gloss White #2320 as the primer. This will act as a good base allowing the truest top coat color representation. If you are applying a dark color, you can always use a similar Fusion color for better hide.
Regardless of the Fusion color used, I recommend to allow the last coat of Fusion to cure for a minimum of 7 full days. Lightly scuff sand the surface with 220-grit sandpaper to create a slight surface profile. This will allow your topcoat to bite into or bond to the Fusion Paint film more effectively.
NOTE: Krylon does not recommend top coating the Fusion Paint coatings. Unfortunately, not all paint coatings are created equally. We are not able to test all blends or paint types with the Fusion Paints. There are, and will continue to be, exceptions to the standard rules established thus far. The main concern would be that the Fusion paint film and the topcoat paint film (oil, latex, lacquer, etc.) may expand or contract at different rates causing intercoat adhesion failure.
Please Test:
Apply the Fusion to a small test area. Allow the Fusion Paint to cure for a full seven days. Next, lightly sand the Fusion Paint film. Use 220-grit sandpaper. Remove the sanding dust with a soft, lint-free cloth. Apply your topcoat paint. Allow the test area to dry and cure for an additional 5-7 days. Test the surface by scratching the test area with your fingernail. It should resist scratching if the paint has bonded correctly. This will give you a pretty good indication of how the product will perform on your particular surface over the long run. If the topcoat is holding well, you may apply the system with more confidence.