all metal or fiberglass filler?
Hey everyone I have one more question. On my other fender I have a small amount of pitting on the back side. I have sandblasted all the rust and treated with acid, I now see a hole about the size of a needle point in the center of where it is pitted. Is it worth usung a skin coat of a fiberglass filler or metal based filler to smooth and fill the pitts and pin hole? Or do I need to try and weld a patch in? I just want the job to hold up. I will also coat this fender inside with a rust preventive coating before reassembly,
The metal must be thin in that area since it has rusted a hole.
If you have the area completely free of rust, and the metal doesn't seem too thin, I say you can fill any low spots with a waterproof filler, and go from there. IMO.
Welding is the way I'd do it (but I have a weldor, and am comfortable using it).
Another alternative that is probably simpler and could work just as well, would be to cut out the area surrounding the pit, back to clean metal (say a square inch or less). Then, use panel bonding adhesive, to glue in another metal patch from the underside (probably wouldn't hurt to apply it liberally on the backside to coat the edges of the patch and waterproof them).
Then, come back on the top w/ quality fillers. By increasing the surface area, rather than trying to spot treat just the speck, things have a better chance of holding up.
Also, give things a really good thorough look overall...chances are, if you see deep pits, it may not be before long that those areas fail (and it's a disappointment when that happens after things have been painted). A gentle poke w/ a pointed object should give you some insight as to whether things are "solid" enough, or if it's just swiss cheese ready to create a headache down the road.
If you do go the welding route, you can place some copper, brass, or aluminum on the underside of the pit through. That will support the weld puddle and guard against burnthrough (plus act as a heat sink against warping)...sometimes, when all you have to work w/ is a lot of swiss cheese, that's the way to go (welding thin crusty metal is certainly more challenging, but plenty doable once you set your mind to it).