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The most commonly used method is what Vance mentioned. Epoxy paint.
That's the stuff that's a two part mix and it's tough stuff. Jim K. is a
painting contractor and he can give you brand names that are available now. I
talked to a painter using epoxy paint a while back for some large columns
exposed to salt air and he said it's expected life span in that environment was
about 5 years.
I know that a zinc coating uses the "sacrificial" properties to create an
oxide on the surface, preventing oxygen from reaching the metal below. Steel,
aluminum, stainless, and probably all metals react that way ( I think.)
In the jobs where I've used it, zinc rich paint exposed over long periods
to weather and sun gets a little "dusty" layer that develops on the surface.
That's the zinc oxide.
We used a paint called "Zincalate" and you had to keep stirring it so the
zinc would stay in solution.
It went on pretty thick and dried to a dull silver. It lasts a long time
when used on metal legs and stuff on the roof. I've seen things over 10 years
old and the paint coat was still complete, although a little "dusty" as
mentioned.
This is on the roof......not submerged.
A friend made a small metal ladder for his sail boat and painted it with
the Zincalate. It lasted quite a few years and was often submerged in salt water
for weeks at a time.
That's what interested me in that Rhino stuff. It's more a rubber coating
than a hard paint. The sales info described it as creating an "impervious,
monolithic " layer on the metal that was flexible enough to allow the metal to
flex without breaking the bond and/or leaking.
If we painted over the Zincalate painted surfaces, it was just for
looks, and the color wouldn't last very long.
I guess the zinc dust would form on the surface as it was oxidized and
allow the colored paint to flake off.
Maintenance comes into play here. Regardless of what paint is applied, at
some point it needs repair. Whether it's caused by scratches or just normal wear
or salt water corrosion, nothin' lasts forever.
Epoxy paint is the norm and it's probably the easiest to repair or "touch
up".
Because we are taking our subs out and drying them daily a good epoxy paint
would probably still win out in an overall test of reliability.
It's expensive to buy, and a pain to spray on, but still has a known track
record with documented results.
I'll still be asking questions about that Rhino type stuff, but for now,
the epoxy is the safe bet.
I think it still runs $600 for a mix of two 5 gallon buckets, part A and
part B. One nice thing though, it comes in all colors ! ( even the dreaded
YELLOW !! )
Frank D.
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