[HoovDaddy]

As Don said, it’s imperative to use SPI Waterborne Wax and Grease Remover when using SPI primer. Their primer is not compatible with solvent based cleaners or acid cleaners. I don’t think heat has anything to do with it because the problem only appears where the filler is (shadow lines). Was the filler completely cured? Or the wax and grease remover you used wasn’t completely evaporated out of the filler when you applied the primer. Filler absorbs moisture, that’s why I think it’s a bad idea to put filler over bare metal. Yeah, it’s the way we did it in the old days, but filler adheres to epoxy primer better than to metal. When it’s really hot out, I reduce with high temp reducer to slow the cure time.