dont spray high build directly on bare metal unless its an acid etch primer like the PPG NCP primer. it will lift AFTER its color sanded, buffed, and delivered...
strip and blast bad rust spots, acid wash the rest and then 60/80 DA and then one wet coat of black epoxy prime.let the epoxy tack off for an hr (70* with 10% humidity) anything with colder temps or higher humidity and it will take longer.
rough out your first mud coat and 80,then spray your high build right over the top of it. after than long block the primer till you just see the black of the epoxy. stop and work any obvious lows, level and reprime.
should take you two primes before you no longer need mud work. then you can 80 long block and prime three times.
