I have a car that is eighteen years old, and it started to develop a little rust behind the wheel wells, so I had to sand it down and repair it with body filler. When that happens, the metal gets pitted. The rust works its way into little pinholes. I thought I would need to remove all the rust so that the problem wouldn't come back in a few years, but a friend told me I could paint over the pinholes with this product instead, because it neutralizes the rust. That allowed me to preserve a lot more of the metal, so the repair was much easier and the result was better. I did some reading on the Internet and learned that I could use Bondo right over the top of the paint. So far it has worked well. Now I am using the rest of the Rust Bullet to touch up other rusty metal around my property. I have used outdoor house paint over the top of it, and that worked well too. The product is expensive, but I'm finding that a little goes a long way.