PAINT 101:
Lacquer dries by evaporation
Enamel cures by a catalyst or combining with air. (this is why a skin forms inside the can even when its closed, and it can not be remixed with the other paint)
The best way to remember is to think of an egg if you dry it out, you can add water and you have an egg again. If you boil it in water, cut it up add water you have a mess, it changes state for the lack of a better word.
To Keep It Simple
There are primers and primer surfacer, primers are for adhesion to metal, fiberglass or another substrate. Primer surfacer adheres but also fills imperfections, the part that fills is basically talc like talcum powder which absorbs moisture. This is why you can not use any primer that contains talc, to seal water from metal.
I don't know of a lacquer primer/surfacer that does not have talc in it.It also was originaly made only for spot repair for quick repairs and had been abused because its quick dry time.
Enamel primer is the only thing to use for any type of body work and with the catalyst (2/PART) it is faster and better than lacquer. BUT if you want to try and seal the metal from oxiation (rust) it also can not have any talc in it.
Epoxy and Vinyl Wash are the only 2 I can think of that have very little talc in them. The paint co. call these shop primers since they sill don't want them in outside exposure, but they seem to work good for limited exposure (rat rods)
REMEMBER SAFETY FIRST !!!!
WEAR AN APPROVED RESPIRATOR (PAINT TYPE ONLY)
ESPECIALLY WITH ANY 2/PART PRODUCT
