2 * 2.1 SD

[Dieselman]

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.

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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.

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The right side was similar, but a much smaller patch.

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After chipping and acid treatment.

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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.

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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.

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[Julianw]

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

[Dieselman]

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.

[Dieselman]

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.

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[Julianw]

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...