Dear List,
I am pretty sure the weld-through coating I tried was the expensive 3M
stuff. I don't remember for certain, but I do recall feeling I had wasted
a significant amount of money.
Basically, the coated metal welded as if the metal were dirty or rusty
(not too surprising), and it was hard to get a clean weld. I cannot
check, because I chucked the can in disgust, but I suspect weld-through
coatings are intended more for spot welding than for mig welding.
I don't recall if the coating was a zinc-rich coat or not, but it is
definitely not good to breath zinc fumes. I try to weld galvanized metal
as little as possible, and when I must I make certain to work in a
well-ventilated space. Note that brazing alloys contain zinc. I consider
brazing to be outmoded for body work but you may have to eliminate braze
applied by the DPO. If you melt it out, don't breath the fumes.
The Spridget restoration book by Porter touts a cold galvanizing paint
(zinc rich paint) for use inside box sections and the like before welding.
Aside from the fumes these produce when hot, I've found them to make
welding nearly impossible. The coatings are also fragile, and I cannot
imagine they do a lot of good--one can scrape the stuff off with a
fingernail, or damn near, unless you really rough up the metal. Smearing
the stuff on a new shiny panel, as shown in the books, seems to me a waste
of time and money, but YMMV.
I have an unconventional suggestion for the important business of
rustproofing box sections and the places where panels overlap, and I would
appreciate feedback from anyone else who has tried it. Up here in the
frozen northland, land of salt and maple syrup, an old time farmer's
prevention for rust is to spray old engine oil under the truck (car,
what's a car? How many calves will one hold?).
I have seen the results of this on a 10 year old Blazer I was fool enough
to buy, and on a 12 year old horse trailer I was fool enough to pull
behind it. The Blazer, which had never been out of VT, had shiny black
paint on the frame (under 1/4 inch of oily grunge). When I removed the
door trim panels to install speakers, the insides of the doors had one
thin coat of primer, covered with a film of oil, and NO rust. Normally,
the Blazer is one of the most rust-prone vehicles this side of a Fiat 850
Spyder. I think the sequence is Fiat, Alfa Romeo, Blazer, Chevrolet Vega.
But I digress.
Oil is inferior to rustproofing in areas subjected to road spray--it will
wash off of the wheel wells in a trice. Only remnants of the Blazer wheel
wells remained. In relatively protected areas, however, oil stays put and
*best of all* it wicks by capillarity into crevices and folds.
Among the first places to rust on cars up here is where two or three
sheets of metal overlap--around the bottoms of doors, trunk lids, and
hoods. My prescription to slow or prevent this is cheap, cheap, cheap,
but on my 7 year old H***a Prelude it has worked, as the Brits say, a
treat. Fill a pump type oil can with 40 W oil. I don't use used oil, I
use fresh. Stick the spout in every drain hole you can find along the
bottoms of the doors, hood and trunk, and everywhere else that looks like
a potential rust area. Squirt a half teaspoon of oil in every hole.
Repeat when the mood strikes. This takes perhaps 10 minutes, a couple
times per year.
Over a year or so, the oil will wick into every seam. The downside is
that the stuff keeps creeping. If you don't wash your car for a couple of
months, there will be a black greasy line along the bottom edge of the deck
lid and doors. You probably don't want to do this if you intend the car
for concourses, but it is well worth the trouble for drivers.
I doubt this method will do much to stop active rust, though it should
slow it down. On new or freshly repaired cars, though, it seems to
work very well to keep rust from getting a toehold.
When I finished painting Kermit, I waxoiled simple box sections. Where
there was a lot of overlapping metal (e.g. the frame rails) I used a
mixture of waxoil and oil. In really tight fitting places, such as where
the outer rear fenders are spot welded to the inner fenders, I trickled
pure oil along the inside of the joint, and put a layer of waxoyl over
that. Before shows, I have to wash the outside flange, because oil keeps
creeping out :-).
One last hint--if you try this, or any other rustproofing, do it AFTER
painting. Do it before, and the oil will play heck with your paint job.
I talked to one fellow at the AH club conclave a couple of years ago, who
said he had rustproofed his AH3000 frame after all the welding was done.
I said, "before you painted it?" and he said yes, and it had been pure
hell to try to get it painted after that. We get too soon old and too
late smart.
Ray Gibbons Dept. of Molecular Physiology & Biophysics
Univ. of Vermont College of Medicine, Burlington, VT
gibbons@northpole.med.uvm.edu (802) 656-8910
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