I use Por15 as directed when possible removing rust and applying to bare metal with the phosphate as directed. I never spray as that is not recommended. I used it in the inner truck lid when I had the lid off, Cleaning out as much inside without taking it apart. I then poured POR15 into it with it upside down and swished the trunk lid so it came out all small drain holes in corners. WHY? Cause I can't get into sand surface rust out and paint. I wanted all inside creases to fill with it as it is a moisture curing paint. The more moisture the harder it gets. I figure it will block any air or moisture from getting to any surface rust and seal it from going any farther. Regular paint breathes and can let moisture thru.
So I figure something to seal light surface rust is better than nothing. Plus POR15 you don't have to mix like epoxy enamel.
That's why I use it and have had good results.
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