"Dave Plowman (News)" wrote:
In article ,
Fredxxx wrote:
The snag with any of these preparations is they just treat the surface
rust. Just sand it down after it has dried to see what I mean. You'll
get back to rust. It might well work ok on fresh thin rust - but not
on that which has been there for some time. Hence the instructions
telling you to wire brush it. So with a spot on a car bodywork, you'd
do more damage attacking it with a wire brush than simply sanding down
the effected area to bare bright steel.

That argument would be true for any steel surface. The advantage of
using phosphoric acid is that it reacts with iron oxide to form a stable
and paintable surface. Removing more steel by sanding/grinding seems an
unnecessary way of reducing what good metal you ought to retain.

Thing about rust is it carries on growing. Especially under car paint once
it has started. And no surface treatment will removed it properly from a
stone chip.

It doesn't necessarily "keep on growing". I have some bits of steel
in my garden (South Suffolk) which I have painted with the "Vernis
pour Rouille" that I mentioned earlier in this thread and the rust
colour under the varnish just remains ast it was when I originally
painted them. Vernis pour Rouille is actually advertised as a way of
preserving the rust coloured look of bare iron and steel.

Admittedly when there's adjacent paint you always have the difficulty
of getting whatever you're using to coat the unprotected metal under
the edges of the broken paint coating. Vernis pour Rouille is very
runny so does quite well at this.

--
Chris Green
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