Two comments. Rust can't continue without oxygen. If rust continues
under POR-15, then it doesn't form an air tight seal. However, I can't
say whether POR-15's claim that it does seal, is true or not. I suppose
one could come up with some sort of experiment to prove this one way or
another.
If I recall, the manufacturers of POR-15 recommends treating the surface
prior to painting with their brand of acid prep, which I strongly suspect
is phosphoric acid based. I'd be surprised to learn that POR-15 wouldn't
stick to a surface prepared with their own product.
Roland
> Hi,
>
> Among the responses to my "Brushing vs Spraying" question, I received some
>interesting responses about using POR-15 on the backside of the rust-free
>steel sheet metal wings on my Healey. In the past, I've heard or read only
>positive testimonials about this product, but now I'm hearing some things to
>the contrary. One person indicated that the product seals in any oxidation,
>and that it (rust) will continue to progress underneath the coating, contrary
>to what the manufacturer claims. Another person indicated that they were told
>the product might not adhere to the zinc phosphate coating left behind by
>phosphoric acid such as used by Redi-Strip, or Oxysolve like products. I've
>always been told the zinc phosphate coating was a very desireable surface for
>a coating like paint or primer. Judging by my past experiences with POR-15, I
>can't imagine it NOT adhering to this type of surface. It sure sticks to
>everything else it comes in contact with.
>
> Anyone like to shed some light on this?
>
> Thanks,
>
> Scott Helms
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