There are three effective ways to apply body filler over RustSeal so that the RustSeal and the body filler bond and fuse together.
1) Apply your body filler once the second or final coat of RustSeal is dry-to-the-touch and does not leave a fingerprint (usually 3-10 hours depending on temperature and humidity).
2) Let the second or final coat of RustSeal fully cure (at least 24 hours), scuff the RustSeal with 300 grit, then apply your body filler.
3) Let the second or final coat of RustSeal fully cure (at least 24 hours), dust the RustSeal with Fusion Self-Etching Primer, let the Fusion cure for 30 minutes, then apply your body filler.
You can feel free to choose the method that will work for you.
RustSeal Product Link 👉 https://www.kbs-coatings.com/rustseal.html
Fusion Self-Etching Primer Product Link 👉 https://www.kbs-coatings.com/fusion-self-etch-primer.html
Please review the complete RustSeal Application Directions before you begin your project.