Incremental body and paint advise

I do filler-type bodywork on epoxy primer base after any weld and hammer work on bare metal. As for the acid note, yes, if the acid stays in the unreacted form it can cause problems if covered, but your timeframe should work well (read the label clearly and do not ignore it). If you are very worried you can (and should) prep the metal again using your normal pre-cleaning steps before epoxy then body work. As normal I also do a 2K sealer coat before paint (just to be clear).

RGAZ