Citroen XM Forum

Before refitting the back bumper I wanted to deal with a few rusty chips, namely where the bumper upper leading edge meets the underside of the rear wings and the very lower wing panel, behind the doors.

A quick look showed a couple of rust spots on the left side, but after paint removal it showed the rust spot was hidden by paint still and about three times larger area, than it seemed.
After quite some time chipping and using acid all the rust was removed, leaving. This is a very close image and any dark spots are shadow. I checked and checked there were no leftover rust spots.
The right side was similar, but a much smaller patch.
After chipping and acid treatment.
I then sanded and wire wheeled these areas to smooth them ready for primer.

The left lower wing panel had three stone chips needed attention, fortunately no rust in these, however I wire wheeled and acid treated to be sure.
All areas were primed. It's a shame that the rear wing/bumper sections come round onto the actual panel, as I was hoping to keep paint repairs to the underside flange only....as I'm rubbish at painting cars.

What acid are you using? I just dug out my lifetime supply of oxalic acid crystals to find that they've not been in an airtight container and are now next to useless. Unless you're using something better and easier to get hold of, I guess I'll be ordering some more

I'm using Acetic acid...white vinegar at, iirc, 20% strength.

Not as effective as oxalic, but easy to obtain, convenient and cheap.

I use a small electric engraver with a sharp, hard, point, to chip into the rust to break it up, then work in the acid using a small wire brush, old toothbrush, paper towel. It's pretty slow, but seems to be effective.
For tiny spots I've even resorted to using a pin held against the engraver to break up the rust spot.
The only issue seems to be the engraver becomes really hot...It's not really deigned for constant use.

Surely the acid content of your crystals hasn't reduced, just showing some oxidisation, they should still be perfectly useable.

Just a rub down and recoat of the primer. When flatting off I rubbed through to metal in a few areas, so another coat of primer was applied.

Dieselman wrote: Thu Aug 06, 2026 6:19 am I'm using Acetic acid...white vinegar at, iirc, 20% strength.

Not as effective as oxalic, but easy to obtain, convenient and cheap.

I use a small electric engraver with a sharp, hard, point, to chip into the rust to break it up, then work in the acid using a small wire brush, old toothbrush, paper towel. It's pretty slow, but seems to be effective.
For tiny spots I've even resorted to using a pin held against the engraver to break up the rust spot.
The only issue seems to be the engraver becomes really hot...It's not really deigned for constant use.

Surely the acid content of your crystals hasn't reduced, just showing some oxidisation, they should still be perfectly useable.

Thanks Will

The wisdom* that is AI tells me that oxalic acid solution goes off quickly, and that the crystals oxidise unless kept completely dry. The crystals had clumped together and newly made up solution with them certainly didn't seem to have any effect. I'll try acetic acid...

To aid with sanding the primer I sprayed a light coat of paint to act as a guide coat.
It was partially successful, but also made sanding more difficult as it tended to cause clagging in the abrasive paper. My recommendation is that for guide coat, use the proper powder version.

I still sanded through in parts, so painted on another coat of primer.
After sanding the third primer coat, it is flat and there is no exposed metal.

Julianw wrote: Thu Aug 06, 2026 8:50 am

Dieselman wrote: Thu Aug 06, 2026 6:19 am I'm using Acetic acid...white vinegar at, iirc, 20% strength.

Not as effective as oxalic, but easy to obtain, convenient and cheap.

I use a small electric engraver with a sharp, hard, point, to chip into the rust to break it up, then work in the acid using a small wire brush, old toothbrush, paper towel. It's pretty slow, but seems to be effective.
For tiny spots I've even resorted to using a pin held against the engraver to break up the rust spot.
The only issue seems to be the engraver becomes really hot...It's not really deigned for constant use.

Surely the acid content of your crystals hasn't reduced, just showing some oxidisation, they should still be perfectly useable.

Thanks Will

The wisdom* that is AI tells me that oxalic acid solution goes off quickly, and that the crystals oxidise unless kept completely dry. The crystals had clumped together and newly made up solution with them certainly didn't seem to have any effect. I'll try acetic acid...

On that note I've found some 40% Acetic acid. Obviously the stronger concentrate, the more effective it will be.

https://www.amazon.co.uk/40-Acetic-Acid ... th=1&psc=1

I had an old tin of mixed paint so decided to use that, but being only small areas thought I'd use an airbrush to apply it. I struggled to achieve decent atomisation so the paint had a poor finish...it looked like stone-chip protection paint.

I tried two coats, both with the same result, so flatted back to a good flat surface. I managed to break through the primer in one very small area, so re-primed that and will have another go using aerosol cans I have found a couple of.

Most of the base coat painting went Ok, but one side has a reaction in the paint, causing a ridge and wrinkles. I'll flat it back and paint again, but may need to strip it and start again.
How it should look.

I had ordered a couple of cheap mini paint guns and was now ready to apply lacquer, so opted for one with 0.8mm nozzle, set it up and mixed up 60g of 2k lacquer at 2:1 ratio...which turned out to be quite a bit too much: more of this later...

I sprayed a light coat, waited five minutes, or so for it to tack off, then sprayed a heavier coat. I waited several minutes and as I still had a significant quantity of lacquer left gave it another heavy coat, to ensure decent coverage and a good shine.
I have a problem when spraying cars, in so much I have no patience and keep over-applying paint. I know I do it, but can't seem to not do so.

The lacquer then sagged in one area and has pooled at the bottom of the door shut, which isn't too much of a problem as being the top coat can be removed. I'll leave it to thoroughly harden then wet sand and polish.
I don't think I've ever made such a mess of painting as I have on this job, I need to be more patient, but just want to finish and put the car back together.
The side where I had access issues has turned out better than the one with ready access.

I am quite pleased with how blending the paint has turned out. I sprayed using mixed aerosol, freehand without masking.

I think my spray painting failure is due to lack to practice and also not feeling the need to put the amount of time into it to learn. I need the mechanical aspects of the car to function perfectly, so persist until they are, but almost feel the exterior paint less necessary, so struggle to find time to practice enough to be proficient.
I'm not quite that bad really and like a shiny car, but do feel the mechanical side is more important, especially on an Xm, which is an unusual and complex car.