Hmm. Can said it can be applied to bare metal or primed. The entire car has been undercoated (professionally, at some point) and there isn't a bit of rust on the car? It's also a FL car, so no chance to salt migration. The rubber should resist the water to penetrate to the metal.Too late now, but one of our resident body guys (Clutch) informed me that undercoat is porous. It needs paint, and shouldn't be applied to bare metal.