Here are some quotes from guys who've used both.
"You would be MUCH better off using Zero Rust than POR15. We used POR for 15 years before we discovered ZR and once we tried ZR we never went back. The POR gets hard and cracks allowing moisture to get between it and the metal which causes more problems than it cures. The ZR can chip or get scratched but moisture can only effect the exposed area right at the scratch because it won't creep under the coating. POR was good when it was the only product on the market but ZR works better and it's less expensive."
"I think the general concensus on this board is that Zero rust is a better product in the long term than Poor por...(pun intended...)
Poor15 becomes very hard and brittle. Its also difficult to repair. In the long run you are much better with zero rust..."
"
trouble with POR is that it is almost TOO hard imo, but when used correctly it holds up OK, but unless you can get all sides of the metal youre painting, chances are it will rust UNDER the POR. zero rust, used in conjuntion with picklex from i understand holds up very well. somewhere on the site len put a picture of something he painted with it that was submersed in ocean water for quite some time, compared to por."
As far as I'm concerned the "BEST" method for finishing metal is to clean everything down to clean metal then prime and paint. However that's impractical for most surfaces under or inside the car so they are usually treated differently. We used POR-15 for a long time and found it to work ok but after opening it hardens in the can and is difficult to work with. After we used Zero Rust one time we never used POR again. The ZR looks better, is easier to store clean and work with plus it comes in colors and costs less. You can check out a test we did HERE and check out prices HERE.
