Can someone please help me understand bondo and paint better?

[aggressive male]

I'm trying to understand why getting metal straighter and using less bondo is always a better thing? Is a lot of bondo like having a lot of layers of paint on your car? If so doesn't water have to penetrate much deeper for it to make the metal rust?

[Gordz32]

Your right! Gettin metal straighter = less bondo. Have you ever seen a car that has cracked repair areas. This is b/c most people back in the day used alot of bondo to straighten damaged areas. They also used it incorrectly to fill holes, heck, some people made panels outta it. The bottom line is. No more than 1/8 " thick of bondo or you'll most likely have problems down the road. As for the rust thing. You shouldn't have rust issues if the metal is prepared properly IE: Neutralized and acid etched, and gaps or ajoining areas are seam sealed. Always get ur metal straight and then use Filler to smooth out any minor imperfections.

[aggressive male]

Thanks Gordz! I also wanted to know if building layers of filler primer or even paint is better than using bondo? I've got a groove I made in my car from welding in new quarter panels. I have to fill a little more than the thickness of sheet metal. Could filling with filler primer be better than bondo?

[yellowrallys]

No, use a fiberglass reinforced filler after you have welded the seam completely.
Personally, I will get the metal as straight as possible, epoxy prime, then put on something like Dynaglass. After working the DG, regular filler or 2 part glazing putty if needed.

[Gordz32]

As yellowrally said, use a reinforced fiberglass filler first. But b4 that, make sure that ur welds are nice a clean. Then apply uur filler. After that lay down some PPG DP90 and then do your finish body filler. That works well 4 me.

[aggressive male]

Thanks guys, Now do you guys really mean I have to weld a bead all the way across and it has to be air tight as if it were a submarine? Or is it ok as long as it is real solid? I already tried to seem weld with an arc welder and kept burning through so instead I got the replacement panel the exact same size as what I cut out and got the 2 flush with a backing plate spot welded behind the new and old metal. In other words, no over or underlapping so I only fill the groove between the sheets. Will this last as long as I use enough spot welds?

[Gordz32]

Jsut make sure the welds are solid. The only time I'd worry about it being like a submarine is if ur running a big hp engine that will twist the and flex the body.

[aggressive male]

Thanks!

[yellowrallys]

Weld it solid with many spot welds, skip around the panel so you don't build heat in one area. Do not leave any unwelded seams, they will come back to haunt you.