rust question - bondo alternative like JB Weld?

[GunsMadeAmericaFree]

We have an ~14 year old Dodge Caravan that is still going strong driving wise, and the interior still looks good. We purchased it used a couple of years ago. Within ~ 6 months of buying it, I noticed bubbling in the paint in a few areas. The bubbling was becoming more and more pronounced with time, and last month I decided to wire brush it with my son. What we discovered were numerous areas with what appeared to be wet bondo all over down low on the vehicle. The bondo was essentially soaked with water, and the metal was rusting a lot because of the water that was being held there. We removed all of the rust, and now there are large gaps in areas.

I remember using something called extend on rusty areas after sanding years ago, and it helped stop rust. Would using something like that be a good idea here?

Also, I'm concerned about the fact that the bondo that was used on here previously was holding water there against the metal. Is there something I can use instead of bondo along with fiberglass fibers to fill in the open areas that won't absorb water? I am tempted to use something like JB weld with the fiberglass fibers, since I've never seen JB weld absorb any water. It would be expensive, but I've never seen any similar product for filling in holes in auto repair.

 

[mindless1]

Polyester resin and fiberglass matting, is waterpoof and more economical than JBWeld, and more flexible so it won't crack apart like JBweld, but will eventually come off. There is also epoxy resin meant for fiberglass, is a little better and a little more expensive but should stick to the metal better so worthwhile.

If you want something long lasting you have to weld in new metal.

If all holes are tiny then bondo also makes a bondo glass and a bondo hairs formulas that have shredded fibers in them, and are also waterproof, but IIRC are in between the flexibility of the resins and JBWeld. The main reason to use these would be if you only need a little (pint? quart?) can, then it would be cheaper, but you wrote "large gaps" so I doubt either of these will be what you need.

The problem you had was probably not that bondo absorbs water, it's that the paint over it failed to keep it sealed because the filler didn't adhere to the metal good and/or cracked away from it, OR they did the job half-arsed and only slapped bondo and paint on the outside then let rust keep growing from the inside.

 

[thedarkwolf]

How much do you actually care? That is my old beater 89 caravan BTW. The proper way to do it is cut out the rusty bits, weld in fresh metal, bondo, blah blah blah it isn't worth enough to bother. I could have made the finished product look a lot better by more sanding and more bondo but again not worth the effort, it is a beater that just needed to pass inspection. Anyway knock off the worst of the rust, naval jelly to stop any active rust you don't get, chicken wire the holes, cardboard or some other backing to help hold the bondo, bondo, some sanding, paint, and your done. Sold it 6 years later and it was still "ok".

 

[mindless1]

^ Older cars don't have to look like beaters. My oldest gets washed, waxed, tires cleaned, interior too. This spring I'll repaint the roof rack and front grill. Only thing I haven't bothered with or plan soon that it needs, is redoing the clear coat in the wheels... putting that off until it's time for new tires.

 

[thedarkwolf]

No of coarse they don't but that one was a beater and it looked like a beater. Some cars aren't worth the effort and it only matters that the run, drive, and the a/c works . My 95 miata on the other hand isn't a beater and when it needs rust repair and it will it, rockers rot on them, will be done correctly.