Bondo?

What's everyones opinion on bondo? I need to try and take care of some rust. I've heard it's better to cut it out and weld sheet metal back in.
Justin

 

Bondo will not cure rust. It's like cancer, you have to cut it out. New panels welded in w/proper surface prep and paint is the only cure. That, or a fiberglass tub.

 

Bondo is heavy and it cracks. that being said, it can be a stop gap method, but it doesn't cure the rust. If you use it, make sure you cut away the rust stuff first and patch with Bondo or fiberglass if you can't weld in a patch.

 

Body shops routinely use bondo, but the good ones only use it in a very thin layer. Its purpose is to shape body contours that have been distorted in the process of repair. If the panel is taken down to bare metal and roughened with 40 grit, bondo will stick fine. It's porous though, so it has to be top coated otherwise the underlying metal will rust.

As mentioned above, Bondo does nothing to fix rust.

 

Bondo will actually speed rust because it is very porous and will allow moisture to enter it, which means mositure is then trapped right at the surface of the metal.

One quick fix you can try, so long as you're not worried about long term (5+ years), is to cut out the bad section, wire wheel a clean surface, spray the surface with an epoxy primer, then use a fiberglass patch. If the section is small enough, you can actually use a product such as Duraglass or Tiger Hair as a gap filler. Both contain fiberglass. They both apply and harden quickly.