Steel patches
 

Starting to develop a small rust bubble on my passenger side rear fender above the tire. I could do what some people do by sanding it down, and wire brushing the steel until it's all gone. But I have a feeling the rust is happening from behind the area where I cant get to, which means the rust will just come back. So a friend of mine who works at a collision shop said he would help with repairing it. I think I would cut a square section out of it about the size of my palm, then tack weld in a new piece of steel that's bent and shaped to fit the area. I have a few large piece of stainless steel sheet metal in my garage. Can I use that or do you need a specific type of steel for something like this?

Stainless IS a special kind of steel. It's special in that it's hard to weld. I would expect you to be blowing holes in the surrounding steel instead of making a clean weld, unless you are REALLY good with a welder. I'd also be concerned that a complex curve in steel is hard to duplicate.



If you flake off the paint, you may find more rust than just in the one spot. Flake off what will flake off, then scrape off what paint will scrape off from near the bubble. Sand all the rust away, all the way down to the steel so it looks like just shiny steel. Only if you end up with a hole in the car do you really need to put new steel in place. Feather the edges of the remaining paint. Clean with acetone or similar and immediately hit it with a good primer, then maybe a skim coat paint. Unless the paint is damaged or misapplied, this rust will (likely) never come back unless it's rusting from the other side.



You'd need to do all that to weld in a patch, as well as the metal work.