Fresh blasted metal is an ideal surface for POR15 to adhere to. No other prep is needed, just brush it on.
This stuff is tough, but not tougher than metal! If you can cut the metal, you can cut the metal coated in POR15 too so don't let that be a factor in your sequence.
That being said, POR15 adheres great to oxidized metal too. So if you left the metal for a while and it had minor surface rust you could then brush on the POR15 with absolutely no downsides.
And THAT being said, bare metal, kept in a garage won't rust...except where you touch it...or like happened to me, my kids had a squirt gun fight in the garage.
I had a car in bare metal (portions of it) for over a year and no surface rust set in even though the doors were open on 100% humidity days. It only rusted where I touched it, or where water directly touched it.
So in the end, it shouldn't matter whether you POR15 it now or later unless it's going to be sitting outside.
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