Im not certain what was used I would assume sand but that would be a guess. In regards to the primer it is a 2K epoxy primer from SPI. I have done some spot checking in various other areas of the cab and have not noted rust under the primer. I might go back to the location and see what the extent is. That being said if I moved on in the build I would always be nervous that rust would rear its ugly head eventually. I new I should have kept it with the old patine and let well enough alone.
Thanks,
Eric
Eric, not to split hairs here, but is it Epoxy or is it 2K? They are not one in the same. About 3 coats of epoxy and it will seal out moisture from your sheet metal. 2K is their high build primer, which is a more porous paint, it does not seal. So if you indeed used 2K primer, it is possible that moisture crept through the primer and rusted the panel. If it is Epoxy Primer, I would lean more toward media blasting/prep being the culprit.
