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Aluminum trim can be the most difficult type
of automobile trim to restore. Nearly all automotive aluminum
trim is anodized. For the most part this is clear, but some
Chrysler and Ford products can also have gold anodizing.
Anodizing prevents aluminum from oxidizing. It is an
electro-chemical process. In simplest terms, the piece is put
into a solution of water and diluted battery acid while an
electrical current is passed through the aluminum. The
anodizing actually “grows” out of the aluminum as an oxide. It
is not an applied finish like chrome plating.
Anodizing creates a very hard and non-flexible finish, and
causes some serious problems. Anything that cracks or
penetrates the finish will allow water, road salt and other
chemicals to attack the underlying aluminum. As is the case
with pot metal, the result is corrosion and pits. Aluminum is
also sensitive to temperature changes. Most cars are exposed
to seasonal fluctuations, and aluminum does expand with hot
summer days and contract with cold winter nights. Owing to the
inflexible nature of anodizing, expansion and contraction of
the aluminum causes small cracks and fissures to occur on the
surface. Rear panel aluminum trim, near heated exhaust gasses,
usually suffer the most damage. The level of deterioration is
not fully detectable until the anodizing is removed by sanding
or by stripping it off with caustic soda.
Look closely at aluminum grills, headlight trim, rear finish
panels and trim you will see what looks like tiny specs in the
anodizing. These specs are all pits underneath the surface and
there can be thousands to deal with in order to restore the
piece. If moisture and exhaust fumes reach the back side of
the trim, corrosion will also be present. This is a limited
amount t of sanding and polishing that can be done on aluminum
trim without going right through the metal.
Once aluminum trim is restored, there are choices regarding
its finish. One can anodize the trim to original factory
finish, leave it as-is and from time to time polish the trim
to remove oxidation, or clear coat the trim with an epoxy or
urethane finish.
If you are doing a 100-point car that will be judged you will
want to re-anodize. This is an expensive process that not many
companies offer. I can clear anodize or color anodize aluminum
but it does add a substantial amount to the restoration cost.
In addition to cost, a hazard of re-anodizing a restored piece
of trim is that if you have to make any adjustments to make
the trim fit properly or line up with accent pieces, you will
crack your brand new anodizing. When light hits the piece from
certain angles, it will cause a rainbow effect in that area.
If your car is not being restored to the highest levels of
scrutiny, I advocate either leaving the restored aluminum
alone and polishing as needed, or applying a clear coat to the
surface. As with chrome plating, there are many companies that
do industrial anodizing, but they will not deal with
individual car parts as rare and valuable items. I regularly
send trim to different firms to test the results. Typically,
scratched and bent trim is returned. |
Important, Please Read This
Nearly all aluminum trim in anodized from the factory to
prevent oxidation to turn a shiny piece of metal into a dull
one. The first step in the restoration process is to strip off
the anodizing using a solution of caustic soda. Small items
can be stripped on site; larger pieces are sent out to be
stripped.
Virtually every piece of aluminum trim, especially any pieces
on the front and rear of the car, will be prone to pitting.
Anodizing is a hard and inflexible coating on top of the
aluminum. UT us actually an oxide that forms on the surface
when the piece is submerged in a solution of diluted battery
acid and electrical current is passed through it. Anything
that fractures, cracks, or otherwise compromises this outer
layer will allow moisture and chemicals to attack the
underlying aluminum. In severe cases, this corrosion can
perforate the piece. This kind of perforation can not be
repaired.
 Because grills and other front end aluminum trim are bombarded
with sand and other debris, they are usually pitted and often
very badly pitted. The trim on the rear of cars is susceptible
to pitting because of the exhaust, more so on the side of the
exhaust pipe. Interior trim also can be covered with pits. In
most climates, especially in northern states where the
temperature can vary from 20 degrees below zero freezing to
well over 100 degrees, the pitting is more severe. The
aluminum expands and contracts with temperature changes and
causes small fractures in the anodizing allowing moisture to
attack the underlying metal.
The process to deal with these pits is to simply sand them
out. It is actually not that simple. Because of contours in
various pieces of trim, not all of the pits can be reached.
Additionally, not all pits can be sanded out without risking
sanding thru the trim, especially on the edges and corners.
Aluminum trim is usually very thin and can be easily warped if
too much heat is generated by sanding or polishing. There is
no way to polish aluminum with anodizing on it. The anodizing
must be stripped off before any repairs can be made. Pits in
aluminum are usually a mush bigger problem that dents or
scratches, and often it is impossible to remove all of the
pits.
After the piece is restored, it can be re-anodized, clear
coated, or left alone and polished occasionally. Anodizing is
expensive, can easily double the cost of restoration, and will
also add to the time frame for the entire job. I do not do the
anodizing myself, but have a trusted source if you decide you
want the factory finish re-applied.
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