I'm going to paint my engine compartment completely in POR15 but I have a few questions. Now my one strut tower and began rusting which is why im using POR, but the 90% of it still has good paint. Should I scuff up the good paint before I POR it or what? What grit sand paper if so? The paint is already stripped of the top of the rust, just wondering about how to get it to stick to good paint.

 

You can scuff it-220 grit-150- whatever. Por-15 really flows out nicely so a heavy scuff won't show thru. But--if only 10% of the paint is bad, it would be more economical to just paint the rust w/ por-15 then top coat it and the other 90 % good paint with a less expensive paint. The advantage of por-15 is over the rusted metal-it isn't as tough when its put on over other paint.

 

You can certainly apply por-15 over paint, but you're wasting your time. In order to get the benefits of the rust prevention, you need to apply it to bare metal.

Mathius