Yes, it is nasty stuff, but it works. I went half with a friend on a quart container & poured it all in glass baby food jars. Try to use it as fast as possible. If you seal it in a container & it's not quite full, it will harden with the air that's inside.
Yes, it may peel if applied over a smooth surface. It's made to go over rust, so don't grind the rust down to shiny metal, leave some for the POR-15 to stick to.
Make sure to rough it up before applying paint or primer. As for exterior finish work as WODNEK mentioned, it is not the easiest thing to smooth out, goes on pretty thick. Would work though for filling in a low spot from heavy rust. Paul.

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1984 300CD red/blk 290,000 partial resto
1980 240D 4 sp Brn/palomino gone
1997 Mazda Miata STO edition wife's baby
1988 Lincoln Mark VII LSC next resto
1986 Subaru GL wagon daily
1993 Isuzu pickup field beater
2008 Honda Civic EX-L 5sp wife's new car
1978 Honda XL350
1974 Honda XL70 my Calif. ride in HS