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I was changing tyres just now and since the current car (VW Caddy) it a bit longer than the old one I had to turn it around once to change the front wheels. Not paying attention at that moment, when I went backwards, the jack was still up with one rear wheel.

I guess the suspension didn't mind that much, but the jack scraped along the attachment point and removed a bit of the black (or paint colour, apparently) and grey rubbery material (which I guess is corrosion protection) there:

enter image description here

As far as I can tell that's not immediately metal underneath there, though I'm not quite sure what it is.

On a scale from »repair immediately« to »since it's no longer winter it can probably remain like that for a week without further damage« how bad is this?

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  • It's better to seal it as soon as possible, so moist and dirt get no chance to get in. Those fasten the rusting process. Any coating or sealing will adhere better too while the surface is still clean. You can just use generic silicon sealant to cover it, or use a more advance kind of coating if you really mind. You can use a block of wood next time to keep the jack from damaging the car.
    – Bart
    Commented Apr 2, 2018 at 14:46
  • Block of wood and lowering the jack before driving. As noted, it was rather stupid.
    – Joey
    Commented Apr 2, 2018 at 14:52
  • I didn't think VW made cars with fiberglass, but that surely doesn't look like metal to me. It looks almost translucent (... transparent aluminum anyone?)
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Commented Apr 2, 2018 at 20:14

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It looks like the underbody coating got peeled of, exposing the zinc-coated sheetmetall. The photo does not show the zinc being ruptured, albeit the mentioned dynamic makes it possible that the rust barrier got penetrated. Either way the thick coating needs to be repaired as it protects the zinc from mechanical (stone chips) damage.

I would cure this with several layers of spray-on-wax. Should you want to make a 100% solution you could apply some zinc spray before the wax. There are several wax sprays especially designed for underbody repairs. Should there be the tiniest rust visible you need to remove it mechanically as the rust will grow under the new coating.

About the priority: When you see rust you are too late. You should get that in order as it seems to be fine yet. You definitely should clear it before the next winter or holiday near the sea

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That definitely is a strange looking "metal." If in doubt, I've had pretty good luck with this rubberized undercoating. It boasts a "rust encapsulator" formula as well. Remember, prep is 90% of it working properly. Also as a preventative measure, you can buy rubber caps/pucks for jacks and jack stands from multiple places, so you never have and metal to metal.

As far as urgency, it sure doesn't look like it'll make your car fall apart. Of course the sooner, the better.

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