In a message dated 96-09-15 18:35:26 EDT, you write:
<< I have seen various types of "Rust stop" paint. The can says to just spray
it on and the rust will stop spreading... I'm not so sure about that. >>
RUSTY METAL
Some products, like Rust Oleum's "Rust Reformer" and Locktite's "Extend" are
essentially phosphoric acid with a vehicle that forms a protective coating.
The phosphoric acid converts the iron oxide (rust) to iron phosphate, and
the coating then seals the area and provides a better bond for primer and
topcoats.
I've had some impressive experiences with these products. The Rust Oleum
stuff is a latex-based product which (at least this is the only way I've ever
seen and bought it) comes in a plastic squeeze bottle. You pour some out and
spread or paint over the rust after having wire-brushed the loose rust away.
I've applied this to really rusty mild steel and then proceeded to leave it
outside for two years, and the surface never re-rusted in that time. It
forms a purplish-black coating.
The Locktite product (again, in my experience this is the only way it comes)
is an aerosol, and seems to be shellac-based. Application is via spray, of
course, after wire-brishing all loose rust away. Similar purplish-black
coating, but somewhat thinner and smoother. I've been using this on tools in
my garage workshop, to prevent rusting. The coating isn't too durable if the
tool is used (ie saws, etc.) but if left undisturbed it holds up to weather
fine. I've not tested this as rigorously as the Rust Oleum product, but the
spray application makes this quicker and easier. I do, however, suspect that
the Rust Oleum stuff is at least as good due to the thicker coating.
Besides the above, good old fashioned Rust Oleum #69 Damp-Proof Red Primer is
a great product. It has a fish-oil base that penetrates and seals rust, but
(just like the above products) the more you can remove first, the better.
There are more exotic materials like POR-15. I've had a few gallons of this
stuff since the '70's (probably no good now) but have never cracked a can
open. I've heard it's thick and gloppy, but I have no real info.....
CLEAN METAL:
The old standby, zinc chromate (zinc chromate dust is a powerful carcinogen
and zinc chromate is still in lots of inhibitive paints) works fine. DuPont
has a great epoxy automotive primer called Corlar (which I suspect still
contains chromates). This is extremely durable by itself and is approved by
DuPont for weather exposure without a topcoat, something that they DO NOT
recommend with normal primers despite the legions of cars being driven around
in primer for years on end. I have used this and love working with it -- and
the durability is as good as DuPont says. Aircraft and military sources have
epoxy zinc chromate or strontium chromate (pretty much the same danger as
zinc chromate) primers like GlidPlate and RandOPlate, and also non-chromated
epoxy primers like Randolph's Epibond. We use these on chrome-moly and mild
steel aircraft parts after sandblasting and metal-prepping. The FAA / US
Military considers these standard and acceptable. There are also wash
primers which are chromated and also contain phosphoric acid to etch and
convert microscopic amounts of rust.......
More than you wanted to know??
-Karl
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