So I let my girlfriend drive the car. We filled up at a gas station, and when leaving she drives off the curb instead of the ramp, and the curb hits the car's underside with a loud *THUNK*. I checked it when I got home -- no dents, but some black rubbery stuff was scraped off the bottom. Do I need to worry about rust in the newly exposed area? Should I get some spray on undercoating?

Cliff notes:
1) Scraped car bottom on curb.
2) Black rubbery stuff came off.
3) Worry about rust?

 

if it is down to bare metal, yeah it will probably get a bit of rust, though if your in a area like me. It's not anything to worry about.

The rust that eats cars is the sort that starts inside a body pannel due to poor drainage. I suppose if your in a area that has salted roads, you should worry about anything bare though.

A spray on paint or undercoating should work fine, just make sure that you prep the area well so it sticks.