How quickly can rust form in a scratch?

[a3103]

I've got a deep (but small) scratch in the bonnet of my A3 (57 plate) which has a small amount rust at the bottom of it. Does anyone know if rust can form within one week from the time the damage occurred? The scratch does appear to have gone through all the paint layers.

[zollaf]

welcome. in the right conditions, rust can form on bare steel within a few moments.

[AudiDave]

I put some rust converter on an area that gained rust, waited for it to turn black and rinsed it off. I'm not a paintwork expert but it seemed to work ok, this was on an older car mind but it's an option

[keithwigley]

Drive your car around the block and carry out some heavy braking at various intervals to shine those brake discs up to a high polish. Put the car on your drive and splash some fresh water onto the discs. Wait to see them turn brown with rust in seconds rather than minutes. That is how quickly rust forms.

[dazler1527]

instant if it is open to the elments(oxidisation) i had a customer bring a newish car back to me with the nearside rear wing badly damaged and woundered why it was going rusty 2 months after reversing down the side of her house.

[vwcabriolet1971]

Scratch needs to penertrate the paint layers for rust to form . The zinc coating on the bare steel will help to stop rust spreading quickly but any bare steel surface however small or narrow will rust.