On Wed, 14 Jan 1998 07:42:55 -0800 "Lawrie Alexander"
<Lawrie@britcars.com> writes:
>For us modernists convinced of the efficacy of Bondo, please explain (a)
the benefits of lead, (b) where one obtains lead of the proper
consistency for this job, (c) what method of heating you use and at what
temperatures, and (d) how one prevents gravity from letting molten lead
flow straight out of a repair area, for example on the underside of a
rocker panel. Inquiring minds want to know....
Wow! I nearly skipped this one until I noticed the word "lead". Since I
have done this once in my entire life, I'll take a crack at it.
Lead makes a (very) permanent repair if done right. It's strong, doesn't
rust or corrode, doesn't deteriorate or crack from ultraviolet light or
from flexing, and it takes paint well. It is especially good on a body
panel that is subject to stresses and flexing. The thicker it is
applied, the stronger the panel gets. This is an old technology that is
still being used every day. Many new cars have a leaded joint where the
roof (hard top) is attached to the body posts. It's a vanishing skill,
but not a lost art.
I understand the concern of some environmentalists and some health nuts,
but the word is, just don't consume the stuff. If you melt it, drill it,
file it, or hand sand it, it falls on the floor and you can sweep it up.
However, if you have in mind to power sand it, you had best have a very
good filter respirator mask.
That said, it was not nearly as difficult to do as I had anticipated,
took just a few minutes to get the hang of it, then came pretty easy.
The first order of business is to get the steel surface clean and tinned
so the lead will stick. Soldering on aluminum is a lost cause, because
as soon as you apply heat it forms an oxide coating that prevents
adhesion of the lead. Once the steel surface is tinned, the rest is a
piece of cake.
When lead melts it has a gradual transition from solid to liquid. It
doesn't suddenly flow like melting ice into water. It behaves more like
butter being warmed up until it is soft, the warmer it gets, the softer
it gets. Too cold and you can't work it, too hot and it runs off. You
play the flame of a torch around on the surface to apply heat evenly over
a sizable area. When you get the surface temperature right you can push
the lead around with a hardwood spatula like frosting a cake. You can
even apply body lead to vertical surfaces. An inverted surface would
probably be more of a challenge, but not impossible. Like bondo, you
want to build it up slightly above the surface. Once it cools you just
file it to the finished shape, and it's very easy to file. I understand
that the current day skilled technicians on the production line can
usually get it smooth enough on initial application without sanding or
filing.
The "lead" is actually a tin-lead alloy like solder. You need the right
alloy, either 50-50 or 60-40, I don't recall at the moment, but if you
buy it at the body materials supply place you get the right stuff. It
typically comes in half pound bars, long and skinny. Last time I bought
a bunch and only used a little, so I probably have a life time supply
left over. If you're careful, most of it should end up on the car body
and very little on the floor, so there should not be much waste. Don't
try using the lead from an old battery or wheel weights, those would be
nearly pure lead with no tin. You would also need a hardwood spatula, a
bottle of soldering acid, and some of those little pencil brushes to
spread the acid on the hot surface.
My car now has another 10 years and 125,000 more miles on it. It's ready
for a little more body work and a repaint, but that spot with the lead on
it still looks like new.
Barney Gaylord
1958 MGA with an attitude
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