On Sat, 06 Nov 2010 19:53:40 +0000, Theo Markettos wrote:

I have some steel car bodywork that's rusty and wants treatment - mostly
exterior edges of wheel arches. I think the metal is good underneath,
so it's just surface rust.

I don't know - most times I've seen that, it's either coming through from
the reverse side, or via the join between inner and outer wheelarch - and
it follows the iceberg principle, where there's always ten times more
than you can actually see :-(

I've been sanding off the rust with sandpaper and a sanding block, and
some good metal is coming up, but it's quite pitted and will take an age
to sand off all the good metal to make a flat good surface.

Yep. You can skim-coat it with filler, and you can get thicker primer
paints that are designed to be sandable and take up some of the slack.

That of find a very large sacrificial anode, PSU, and bath ;-)

I've been thinking of using a wire brush in a power drill, something
like one of these:
http://www.toolstation.com/shop/Powe...ire+Abrasives/
d80/sd1920

Problem I found with steel brushes were that they took away as much good
metal as they did rust and paint. Brass is probably better - or go with
some kind of sand-blasting (if you have access to a compressor you can
DIY)
Once I have bare metal, what's best to prime it? Use the Jenolite to
treat the surface? Or straight Hammerite? Or I've heard it suggested
using zinc primer (Zinc 182?), or an epoxy-based primer. I already have
some Jenolite and black Hammerite. This time I'd like to try using the
manufacturer's paint to get a colour match (a few bits are more
conspicuous than undersides of wheel arches, where I might just stick
with Hammerite).

I think I used Hammerite the last time I messed with anything like this.
Then a few coats of thinner primer, then a few coats of top-coat. Mind
you, I was welding in new metal too because some bits were just too far
gone to mess with filler.

And for bits that aren't visible (not cavities), I've heard various
suggestions of using something like penetrating Waxoyl/Dinitrol, or just
engine oil. Anyone any opinions?

I had a huge cannister of waxoyl which came with a pump and spray
attachment, and that worked well. Fiendishly messy stuff, but it did the
job.

The underside has already been
undersealed but the underseal is broken in places.

Do your best to get rid of any broken bits that are flaking - the
waxoyl's going to stick to them, and they're going to eventually fall
off, leaving you with unprotected metal.

I know this is
completely the wrong time of year to do this, but not a lot I can do
about that except copious application of the hairdryer... (or is it
better to leave untreated until summer rather than seal in moisture)?

Are you working indoors or out? If outdoors, well... it's not going to
rust into oblivion in half a year - I think I'd be tempted to just say
sod it and deal with it next year. If indoors though, invest in a
heater...

cheers

Jules