Rust spot on car

Can anyone recommend (through personal use and not hearsay/web hype) a good rust killer plus primer to use on a small awkwardly located rust spot on a car please. Awkward in that its on the crease of a panel and under the rear light cluster which I'll need to take out to properly cure it.
The top coat will be a silver grey metallic fwiw.
Ta
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I would only use a rust killer in desperation. If it has not gone through the metal I would clean back to bare metal with a wire brush, file or wet 'n' dry then use body filler to build up any lost material before painting using a zinc based primer.
Richard
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On 10/04/15 13:56, Mark Allread wrote:

If you can clean it fairly well (>70% bare metal) it's hard IME to beat red oxide primer. Them work up as you wish with other paints.
Years of my father battling a crappy rustbucket Fiat when I was a kid taught me none on the magic remedies work, with the possible exception of phosphoric acid which almost seemed to do some good. Jenolite was crap. Zinc preparations were useless.
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On Fri, 10 Apr 2015 14:26:45 +0100, Tim Watts wrote:

Best thing is engine oil. Bugger to paint over though.
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On 10/04/15 14:56, Jethro_uk wrote:

What, pour on and set light to it? Yes, probably the best for a Fiat...
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On 10/04/2015 14:26, Tim Watts wrote:

Red oxide paint is no longer made with lead oxide. So is red through pigment and purely for marketing purposes.

I think Jenolite has moved on since your father's day. It now contains your phosphoric acid. http://jenolite.net/what.html
Perhaps a local sacrificial zinc anode might help? :-)
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I think it always has done.
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.
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On 11/04/2015 15:11, Dave Plowman (News) wrote:

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.
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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.
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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.
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We're talking car bodywork here. The steel and paint used is rather different to the sort of steel you'll find in a garden.
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I have actually used Vernis pour Rouille on a little patch of rust on our Citroën C5, it seems to be working there as well. I also use it on our steel boat in France (that's where I first discovered and used it).
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Sand (or grind) it down to bare clean steel then repaint. No such thing as a rust killer that works for this sort of thing. It would need to get under the surrounding paint, and none do.
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On 10/04/2015 14:34, Dave Plowman (News) wrote:

Capillary action would probably get phosphoric acid into more difficult spots.
I've successfully used the following on garden furniture and gates http://tinyurl.com/lxftnmx
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I use this on our boat in France and have also used it on various bits of outdoor steel back here in the UK. I seems to work very well. Much, much better than anything I have ever managed to buy in the UK.
http://www.ebay.fr/itm/Vernis-pour-rouille-OXI-0-5-L-/150963433901
It's available at the major French 'bricolage' stores as well, I just used eBay as it was the first hit I found.
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If you're not interested in a lasting repair it 'probably' would. But then just slapping some paint on top of the rust will last a while too.
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Dave Plowman (News) wrote:

I 'repaired' the motorhome body by sticking gaffa tape over the rust then spraying it. It got me through the year.
Bill
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Does tend to put your pictures of aerial bodges into perspective. ;-)
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On 10/04/15 14:34, Dave Plowman (News) wrote:

The correct thing is to remove all loose rust first, then use phosphoric acid that turns any small bits of rust to iron phosphate which is stable and takes paint well, then fill and paint.
The acid doesn't stop the rust, but it turns loose pitted rust that can get water under paint, into good stable phosphate that is more resistant to water creep
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