Best bondo for rust

[m3/e30fanatic]

I have a little rust whole and I thought I'd fix it before it gets worse. Whats the best bondo because i looked for some and was confused because variety. Also what else would I need. The rust is on my valence near my battery tray.

Thanks in advance.

[JasonC]

"Bondo" will not fix the rust hole. It's just going to cover it up and make it look pretty for a little while. Then not to long down the road, its going to start to bubble and blister. You need to cut the rust out and weld in a patch then fill in the inperfections with body filler.

[nmlss2006]

'bondo' is a brand of products, presently owned by 3M. It's commonly associated with fillers. If you actually have a hole and rust on the car's metal, you'll need to treat it (there are various ways), then patch the hole.
The completely correct way would be to purchase the part from BMW, cut it off the car, weld the BMW part in.
The as-good way is to cut the rusted part, weld it, smooth it, apply rust preventative, primer, then wurth stoneguard, then topcoat.
Both these above require serious body working skills - the kind that most professionals don't have, in 2012.
Then there are various other ways, some good, some less so. It depends on the permanence that you wish to accomplish and the size/location of the hole. Pictures help.

[m3/e30fanatic]

Got it! What filler do you guys recommend?

[LavaSurfer]

When I first got my e30 I had a nasty hole under my battery. To plug the hole until I painted it I cut the rot out, applied POR-15 to the area, then patched the hole with fiberglass mat. You could bond over that too and it would at least hold up longer than filler alone. If done right no one would know the difference for a long time.

[Exodus_2pt0]

Got it! What filler do you guys recommend?

The point is that body filler is not an acceptable rust repair.

I will repeat, cut out rust, weld in new metal, and use body filler as a very thin film to correct imperfections.

[bmw325csi]

If you have to use "bondo" for it, use kitty hair, it's a filler reinforced with short strand fiberglass. Be sure to grind all the paint down to bare metal on and around the area.

This is in no way the right way to do this.