I agree with deroid.
I just finished using the Eastwood company lead. I used an acetylene torch and it is much trickier than using Bondo or any filler. It took me a while to get a rhythm down on heat and apply, then paddle. Honestly my wife is better at it than I am.
I prepped my surface using 40 grit sanding discs. I used surface prep wax and grease remover for painting. Made sure there was absolutely no rust. I used the flux which the videos also make look really easy, there is a trick to it. Then pushed and paddled the lead, also kind of tricky. If the lead gets too hot it just beads away.
From there, with a respirator, goggles and gloves I sanded the lead down with 80 grit. Eastwood solder is lead free, that doesn't mean I want to breath it in or eat it as it gets all over me. The stuff sands really well and you will be amazed at how the tinned surface and lead bond.
The stuff is basically plumbers solder, or it might just be plumbers solder. Go on Youtube and watch a couple of videos, most guys are well into their 70's who do this and have been doing it since they were 20. While lead is dangerous and you should be careful, the concerns I see online tend to be inflated.
It was cool learning such an antiquated technique, but it is definitely an artisan process. I see why plastic fillers are more popular, you can be clueless and apply the stuff, but I the fumes are just as toxic. Applying lead took a lot of research on my part, but I am appreciative of the results.
I etched the remain bare metal then covered with Evercoat kitty hair, I chose long strand filler because I want the repair to be strong. I chose ever coat because they state their product is waterproof.. While I was able to smooth about about 75% with lead I sill had the rest to worry about. From there I think I will use the Evercoat metal glaze ultra, which I believe is also protective against corrosion. Evercoat says something about the product withstanding a 500 hour salt test, I don't know what that means.
Wax and grease remover
Free Shipping - Summit Racing™ Wax and Grease Removers with qualifying orders of $99. Shop Cleaning Solutions at Summit Racing.
I purchased this kit.
Includes 5 lbs. of 30/70 lead-basedsolder for serious soldering pros
Summit metal etch
Free Shipping - Summit Racing™ Metal Etch with qualifying orders of $99. Shop Cleaning Solutions at Summit Racing.
A little of this stuff goes a long way, I used bondo before. I used way less of this.
Free Shipping - Evercoat Kitty Hair Fiberglass Reinforced Body Filler with qualifying orders of $99. Shop Auto Body Fillers and Putties at Summit Racing.
I used these dish scrubbers to apply the flux, easier than using the acid brush.(I kept melting the brush)
I purchased these squeeze bottle for the soda water mix. It was just easier than how the old man handled it in the video with a bucket. I wanted to make sure that the acid is neutralized.
This video is better than DVD it comes with.
I hope that this is helpful.