Quote:
Originally Posted by Reiver
I've scuffed it up, so it has some tooth, with good results
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Agree. You need to create mechanical adhesion ("tooth") or you are pissing in the wind.
If tie-coat primer or self etching primer creates tooth, great. But if I did not know for sure, I would scuff it with 120 grit, then put the primer on. POR-15 is like glass and is just about as hard.
Give yourself a fighting chance and beat it up first - thoroughly.
FWIW - I know a tool crib guy at a machine shop. He has cars but no real experience in car painting or finishes. I was about to buy POR-15 for the first time and I asked him about it. First thing he says is "Make sure you scuff it up or no second coat will stick". They base coat machines when they rework them with POR-15 then over coat with green or gray.