'POR15' is a whole system, for best results use it for the whole job.
1, marine clean to clean it
2, metal ready to etch/etc the metal
3, paint with por15
Whereever you buy it from should be able to supply you all the info sheets as to how to use it. Its good stuff, just has to be done right otherwise don't waste your time using it.
Its all I use now, have done a whole floor with it, and it looked like new 1-2 years on. (then sold it) All 3 stages of the job are about as thin as water, so coverage is huge.