Yes. Most body fillers, fiberglass and automotive primers may be applied directly over Rust Bullet. Two coats of Rust Bullet should be applied to the metal surface. The body filler, fiberglass or primer should be applied directly over the second coat of Rust Bullet between the time that the last coat of Rust Bullet is dry to the touch, about two to six hours, up to 12 hours. The previous coat should be dry to the touch and not wet or tacky; if there is no transfer of coating to a gloved finger it is safe to apply a filler. If 12 or more hours have lapsed, wait for Rust Bullet to cure for at least 24 hours then lightly scuff with 80-100 grit sandpaper; enough to break the glaze to create a surface profile. This 12-hour period is decreased in areas with high humidity levels.
NOTE: Fillers tend to absorb moisture which will cause further rusting of the metal and bubbling of the filler if applied directly to a rusted area that has not been protected with Rust Bullet. Rust Bullet works best when it is in direct contact with the metal.