rust questions: cross-posting here

[GoBlueJays]

I have a 2003 Legacy GT with rear fender rust. I sanded down the rust from the outside without opening the fender from the inside (from the trunk or back seat) and apparently I did an incomplete job; the rust came back.

 

I just peered into the inside of the fender from the trunk and it appears the rust is limited. In other words the rust on the outside is not the tip of the iceberg. This makes sense because the rust started because my elderly father was scraping the fenders against the side of his garage--so the rust started from the outside not the inside.

 

Please help me with these questions:

 

1. If I am able to cut out the rust and/or sand down to bare metal, do I have to wash the surface with some chemical to prevent rust from spontaneously reappearing before applying primer and paint?

 

2. Any advice on how to open up the trunk/backseat to get a full and clear view of the inside of the fender (and putting it back together)?

 

3. How warm does it have to be to do this? I'm in chilly Massachusetts.

 

Thanks!

[Dangerzone3]

Generally, the idea is to COMPLETELY eliminate all the rust. Ideally, this is done by cutting out a piece of the fender and replacing it with sheet metal and welding it back on. However, in most people's cases they either don't have the resources or the time. If I remember correctly, the rear fender panel is not accessible from the inside. This would just expose the chassis. I may be wrong though.

 

What most people do is cut out the rusted piece and sand away all the surrounding surface rust. (If you need to sand a large piece, so be it. Don't be afraid to repair a large area.) After making a somewhat of a small whole, you can use a mesh that can be bought at your local body shop. This helps in holding body filler and giving it a surface to stick to.

 

As for temperature, the body filler will have a hard time settling in cold temperatures. As somebody who lives in Canada, I learned this through experience. Just wait until it gets a bit warmer. Plus you don't want that salt from the roads getting onto a fresh paint job.