Rust Repair Part 1: Rust - How to deal with it
The typical rust you will encounter on an LBC (or any old car
for that matter) can be broken down in to 4 basic categories, each
one progressively more severe. These rust categories are:
1) surface rust with little or no surface pitting
2) surface rust with surface pitting
3) rust through / pin holes / this spots
4) rust holes
The first rule of rust repair is that the affected area is
almost always much bigger than it first looks. The first order of
business is to strip the rust area down to bare metal to see how
bad your problem really is. The stripping can be done using a
wire brush, sander, sandblaster, or using chemical strippers. My
personal preference is to use a 4" mini-grinder with a wire brush
attachment to strip off the surface rust, old paint, and
undercoating. You should strive to get down to shiny clean metal.
After you have cleaned to bare metal, you need to inspect the
area. A visual inspection will reveal the obvious problems, but
you also need to poke, prod, and feel (weren't they a 1960's rock
group?) to determine overall condition of the metal. It is common
for the metal surrounding category 2, 3, or 4 rust areas to be too
thin to be left unrepaired. Another thing you need to determine
is if th rust is a limited area or if the vehicle is rusty all
over. If your rust is in a limited area, you should figure out
what caused the rust to prevent it from returning. If the rust is
extensive, you need to examine everything very carefully to ensure
you have found all the rust. It is common on an extensively
rusted car to find a mix of most if not all rust types listed
above. At this point, if you have determined that your rust is
only superficial surface rust, be thankful that you caught it in
time. All you really need to do is trat the area with a good rust
eliminator or rust preventative, then prep and paint and/or
undercoat the area with a quality topcoat system to keep the rust
from returning. Classic Auto Restorer magazine had a good article
on rust treatment products in the december 1992 issue. My
personal favorites for rust treatments are Rust Mort and OxiSolv
for converting and stabilizing rust, and Zymolite Rust-Mate rust
preventative paint.
If you have determined that your rust problems are more severe
than just surface rust, then you will need to preform surgery to
properly repair the area. This can be done in one of 2 ways -
filling in small holes using welding rod or welding in patch
panels. Selecting which method to use should be based on the
overall condition of the metal. If the metal is basically sound
with just a few small holes, then welding the holes closed is the
preferred choice. However, if the metal is thin and has numerous
small holes (like cheesecloth), then you are probably wasting your
time trying to weld all of the holes closed. A patch panel will
give you a better repair. Part 2 and 3 of this article will cover
each of these repairs in detail.
The repair methods provided here are best suited for a MIG
welder or an oxy-acetalyne welder. The beauty of the MIG is that
it provides minimal heat distortion and welds very thin metal and
is easy to learn. The oxy-acetalyne welder is the second best
choice, as it is also easy to learn and welds thin metal. Heat
distortion can be a real problem, so care must be taken to ensure
you don't warp the area you are working on. One nice thing
about oxy-acetalyne is that you can reheat your welds to improve
penetration or to reshape the weld if you choose. This is a nice
feature. TIG welders can do a fantastic job, but are usually too
exotic for the average DIY'er to have access to, and they require
a lot of skill. Arc welders are somewhat unsuitable for this type
of work, since they strike such a hot arc that burnthroughs and
distortion are a big problem. There is an arc welder attachment
called a stitch welder which makes it possible to weld sheet
metal. However, I personally consider an arc welder to be a
distant 3rd choice, even with a stitch attachment. Finally
brazing can be used to perform repairs, but I personally avoid
brazing. Brazed repairs can often crack out, since brass work
hardens over time.
At this point, if you have determined that your car will
require welding and you don't plan to do it right away, you need
to treat the area with a rust-preventative primer to stabilize it
until you are ready to perform the repair. This is important,
even for a rust bucket, or by the time you are ready to make the
repairs the car may be beyond hope.
One final note - rust holes can't be permanently repaired
using newspaper and bondo. Much to my dismay, the PO of my truck
had used this method of "repair" which I discovered when cleaning
up the truck for restoration. What a flaming jerk !
Stand by for tommorrow's posting - Rust repair Part 2 -
Repairing small holes.
Until then - cheers,
Mike Harlan
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