Re: [A/S] Paint vs. clear - durability

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

Roy,

There is no problem in getting paint to adhere to aluminum.  All it takes is
proper surface preparation and the proper primer, and top coat.

A few weeks ago, I posted a more complete description of the factors at work
which cause clear coats to fail, most of which do not apply to pigmented
finishes.

This system has been successfully used on aircraft for years.

Basically it consists of chemically cleaning the aluminum with a phosphoric
acid etching solution followed by a phosphate conversion coating solution
called alodine. (It leaves a light green hue on the aluminum.)

The next step is to apply a catalyzed epoxy resin primer (Dupont Corlar, for
example) followed by a top coat of a good enamel.  The best enamels are
catalyzed polyurethanes (Dupont Imron, for example).

Properly applied Corlar primer over properly cleaned and alodined aluminum
will not peal!

All of these products are available at an automotive body shop supply.

The reason a painted surface will hold up a lot longer than the clearcoated
one is primarily due to the clear finish being broken down from the inside
by ultra violet light - which cannot penetrate a pigmented finish.

Also, for cosmetic reasons, one must use the clear (rather than green)
alodine treatment.  I do not know of any clear epoxy primers either (epoxies
have the best adhesion of any paint).  Thus, with the clear coat, one is
stuck with applying the clear finish (with no primer) directly over the bare
aluminum.  Urethane clears tend to have very good adhesion (though not as
good as epoxies) and are very flexible and sufficiently elastic to handle
the expansion and contraction of the aluminum. The big problem is UV induced
deterioration.

I think this explains the superior durability of the Argosy paint vs. the
Airstream clear.

Oliver Filippi