Auto Body Repair

The first step in cleaning the bare metal in preparation for the lead filler is to sand the area. Sanding is done first because it produces dust, and this needs to be cleaned as well - in one of the many ironies of car bodywork, the process of cleaning the metal generates even more contaminants to be cleaned up. You should use fine grit sandpaper for this purpose, either manually or with a disc sander, depending on how much work appears necessary to take off any protective coatings or oxidation residue.

After sanding, you should make use of a degreasing solvent that will rid the metal of oil and lubricants, both of which can affect lead filler adhesion. You will need some patience and a good supply of clean rags to carry out this part of the cleanup. You should wipe the area with a solvent-drenched rag, then dry it off with a fresh, clean rag, then apply more solvent, and so on. Continue this process until the rag you use to dry the area comes away unstained by any color except the solvent.

After the solvent treatment, the metal must still be cleaned further, this time with tinning flux which etches the rust and other substances out of the surface directly. Liquid flux is the easiest and most direct to use, although there are also paste and powder forms of this substance available. The surface of the metal should be heated prior to the flux application, a task best done with an air-acetylene torch rather than an oxy-acetylene, because of the lower temperatures they generate.

The flux should be applied liberally once the metal is hot enough to make it boil a little on the surface of the car. If the flux steams as well, this shows you that it is in fact functioning properly and eating away imperfections and contaminations embedded in the surface. Once it has stopped visibly fizzing and steaming, the flux has finished and you should remove a good part of it - but not all - with a nylon cleaning pad. Remove all brown deposits but leave a coating of flux on which to spread the tinning solder - the flux gives the solder grip on the surface, and the solder gives the filler grip in turn.