[VAC] Followup - Satin polish and clear coating - To Don Hardman, et al

["Carol and Oliver Filippi" <ofilippi@xxxxxxxxxxxxx>]

Don,

The Aluma Prep and clear Alodine (not the green Alodine) is the standard way
aluminum is prepared for a finish to adhere to it. [The green Alodine is
used when the aluminum is to be painted, vs. clearcoated.]

I have not tried this, so I have no direct experience, though I have done a
lot of painting and other finishing on a variety of substrates. The Alclad
aluminum used on the Airstream may or may not cause a problem.  As most of
you know, the aluminum exterior of the Airstream is an aluminum alloy panel
with a thin pure aluminum exterior surface coating.  If you go through the
pure aluminum exterior surface, all bets are off. [ The color and reaction
to cleaners and polishes will be different for the alloy substrate as
opposed to the pure aluminum surface.]

The way the Aluma Prep is supposed to work is to dissolve the aluminum oxide
coating (caused by weathering, etc.) leaving the clean aluminum metal.  The
Alodine is a conversion coating which is supposed to cause a thin clear
oxidizing of the surface which will not further corrode (oxidize) very fast,
and provide a tooth for the clear coat, thus enhancing the adhesion of the
finish.[The Aluma Prep also etches the surface to improve adhesion] The big
question is, "will the Clear Alodine provide the look we are after?"

The Urethane clears are slick, high gloss, catalyzed finishes which are used
to protect metals and as a clearcoat over a base coat / color coat finish
(Typically used on most cars and trucks these days with metallic colors).
They also have a UV filter (some much better than others) incorporated into
the finish to reduce the damaging effect of sunlight. The effectiveness of
the UV filter will play a major role as to how long the finish will hold up
when exposed to the elements.  [Clear finishes tend to break down from
within, on exposure to ultraviolet light.  Pigmented finishes (paint) are
opaque and are much less affected by UV.]

If the Aluma Prep works, it should be a lot faster and easier way to remove
the oxidation than polishing (or as a precursor to polishing).

Polishing dull oxidized aluminum really scares me, since the oxide is very
very very hard (they make grind stones and abrasives out of aluminum oxide -
it's hardness approaches that of a diamond!) and the plain aluminum is very
soft.  Because of this marked difference in hardness, you run into a
tendency to abrade more of the exposed aluminum than the adjacent dull
oxidized surface when polishing with abrasive polishing compounds (unless,
of course,  they contain chemicals to cut the oxide).

To get a uniform satin finish, it might be necessary to 1) cut the oxide
with the Aluma prep, 2) polish to a high gloss, and then 3) kill the gloss
with a chemical etch (Aluma prep and Alodine).

This sounds like an awful lot of work.

Hopefully the chemical treatment will do the job the first time.

Has anyone tried this?

Note: Aluma prep and Alodine are (or used to be) made by the Nelson Chemical
Co. in Detroit.  They are distributed by PPG/Ditzler autobody paint dealers.
DuPont autobody supply dealers sell similar products made by DuPont.



Oliver Filippi