Can You Use Bondo over Rust?

However, Bondo shouldn't be used on every kind of rust hole. Because it can't support any weight or protect you in a crash, you should never attempt to use Bondo for rust holes in anything structural, such as frame rails or reinforced areas on unibody vehicles (i.e. most modern cars and crossovers).

Can you put body filler over rust?

The mere application of body filler over a substrate won't stop rust, Miller said. Fillers might contain corrosion resistance and slow the process, “but they're not gonna stop it,” he said. Put filler on rust, and “(the rust) may continue to grow,” he said.

Can you Bondo over rusty metal primer?

NO, never. bondo goes over bare steel only. Never over any kind of paint, primer, etc.