Classic Car Rust - A
By Tom Rahm
There isn't a word in the car enthusiast's vocabulary that
evokes more emotion than the word "rust". It's the automotive
equivalent to "cancer". Rust is bad news, no question. It's also
a very misunderstood problem, one that can be easily dealt
with or at least controlled to preserve an otherwise good 'ol
Preservation and Maintenance:
The most serious type of rust is deep panel rot. The metal
actually disintegrates causing holes and other damage. This
requires new sheet metal to be grafted into the panel, or
complete panel replacement. Why does this happen in
certain areas and not others? Prolonged exposure to
moisture. The bottom of a fender, particularly behind the
wheel well is a common area. Over the years of being driven,
dirt and debris accumulates in the bottom of the fender and
stays wet, accelerating the rust process. Other common
areas are quarterpanels, windshield channels and lower
doors. We've all seen rust out.
All cars, whether restored or just beat up old drivers, can
benefit from taking a trip to the Car Wash and pressure
washing these areas. Put the rig on jackstands, crawl under
there and blast that old dirt and debris outta there!! This is the
single best thing you can do to preserve whats left of a future
project, or keep a finished car preserved.
Dealing With Surface Rust:
Surface rust is actually minor and can easily be dealt with. It's
just rust colored metal that doesn't have deep pitting or holes
into the pores of the metal. This usually isn't an emergency.
The rust/oxidation can be sanded off and a non-porous
primer can be applied. Rust Bullet, POR15, or old school
epoxy primer can be used to encapsulate what molecules of
rust remain in the pores of the metal that can't be sanded out.
A cheap easy to use material is plain old Rustoleum. Properly
done, this should treat the rust for good.
This gets a little more involved. The rust has penetrated the
pores of the metal, but not to the point of rust through. There
are materials available that treat this very well. These contain
phosphoric acid, which dissolves rust. You can brush it on
and it will visibly turn the corrosion black. When the wetness
of the material goes away, encapsulate with non-porous
primer and that works pretty well. The non-porous primer
seals the air/moisture away from the corrosion. The corrosion
can't react without moist air to feed it, so it suffocates the rust,
and the rust residue lays dormant under the primer.
Handy tip: Use a power drill with a good sharp bit to nibble
away any rusty residue. You'll see clean fresh looking metal
appear as you grind it out. Cheap and effective!!
Panel Repair vs. Replacement:
As a rule, the OEM sheetmetal parts are much better
stampings than any aftermarket parts. This is why i prefer to
patch as much existing panel as possible rather than replace.
The good news is that there's a huge availability of patch and
replacement panels, and there's no shame in cutting up a
complete panel for just a couple of patches to use. Think
twice before you completely hack off your '69 Chevelle
quarterpanel if it only needs 25% reworked, cuz the new one
might not fit up. This often applies with trunk floors. If the
center section only is rusted, why buy a complete trunk floor
and find out that it won't even fit through the trunk opening for
installation cuz it's too big?
This is in my opinion an expensive impractical procedure.
Most of the rotted ares will be cut out and welded up, and any
surface rust can be dealt with chemically. There are a lot of
hidden hard to reach areas that can't be gotten to with the
blasting equipment, so whats the point? Nibble any rust scale
away with a drill bit until the metal looks clean, then hit it with
primer. Deep rust can only be partially removed anyway, it's
not possible to get blasting media deep enough into badly
pitted metal to remove every molecule of rust, so don't wig out
about rust. Any areas that do require blasting can be spot
It's safe to assume that if you keep your car in a clean dry
garage, or even under a tarp, the weather won't get to it. Don't
drive it in the rain, don't leave it outside all winter, and the
possibility of rust is zero.
Rust is bad news, but it 'aint nothin' to be 'skeered of.
18 wheeler driving muscle car guru. Residing in the pacific
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