So, next jobs I've tackled are the lead loading of the two LH roof joints and the A-pillar to scuttle/air tube area. I got a leading kit for Xmas (thanks Santa!) and decided to now add this to my resto skills portfolio.
The Z came from the factory lead loaded at these locations. The Enviro-Strip baking process however is hot enough to melt all the original lead out. Rather than fill it with bondo etc., I wanted to do it the original way. Lead forms a bond with the underlying steel in a way that filler doesn't, and given these locations are subject to stresses from the flexing of the shell, I wanted to try the OEM approach. I would also be, as with other repairs, putting a thin reinforcing fibreglass skim over them before glazing putty for added strength and future crack-proofing.
For anyone unfamiliar with lead loading, the process entails melting a 70% lead/30% tin (or similar mix) stick onto the target area, shaping it with wooden paddles, and then filing it down. Lead cannot be sanded, given its toxic nature (last thing you want is to breath in floating lead particles!). However, being soft, it files great using a bodywork rasp file and finer files for tidying up.
Cleanliness is absolutely key, meaning no paint. Also, before the lead can be used, the clean steel must be "tinned" - i.e. treated with a lead solder paint. I started with the roof to rear quarter joint. I used aircraft paint stripper to remove all trace of paint (again, no sanding, as a little original lead was still present). After cleaning, the area was painted with the solder. This is then blowtorched until it bubbles and turns colour from dark grey to brown, and then wiped with a cloth, which removes the flux and leaves a bright, tinned layer.
Next, I took a lead bar and heated it with the blowtorch, along with the target area, until the lead goes soft and can be pasted on in blobs.
After that, it is heated up again carefully, and wooden paddles used (dipped in tallow to help stop them burning) to compress and move the lead around to get an approximate shape. Then you get on with the hard work of filing:
Primed without fibreglass or glaze skim:
Close to finalised. Will get more glazing putty when the roof gets skimmed, eliminating any remaining imperfections.