Re: Painting Aluminum - HOW TO DO IT (long)

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From: Ed Tanton N4XY (n4xy@avana.net)
Date: Sun Oct 20 1996 - 20:00:03 EDT


Hi Greg... in two different jobs I held over the years I was involvedone way or
the other in the painting of aluminum. There are several things you must do if
you want paint to stick to aluminum, and when done properly, you can expect it
to do as well as any other paint job.

0. Drill all holes, and finish all surface machining first.

1. SURFACE PREPARATION. First, lightly (or as needed) degloss the surface-if
possible-using a very fine 100-400 grit sandpaper. A matte finish will aide
the paint to adhere. Next, clean the metal surface thoroughly using soap and
water followed by a good degreaser. The best was MEK (methyl ethyl ketone) but
unless you already have some, you probably will not be able to get any. Next
choice would be acetone. You may or may not have or be able to get this highly
flammable solvent-but it works very well against 'grease and oils.' You will
have to do the best you can here. Last resort is alcohol. Remove all traces of
grease, oils, or corrosion/etc. Be careful handling your clean panel-use paper
or clean gloves to keep your body oils from contaminating the panel.

2. PRIMER. Use a quality grade of ZINC CHROMATE PRIMER for aluminum-it will
probably be yellow in color. Absolutely do not put it on too thickly. Paint
with the panel positioned horizontally but apply paint sparingly enough that
if it was vertical, it could not run. Allow at least 24 hours between coats.
Use at least two coats. You should LIGHTLY sand between coats-but remember
that any projections (such as a rivet head) could be scoured of paint and use
great care that they are not.

3. PAINTING. Again use a good grade of paint. What kind depends on your indi-
vidual application. Personally I use hobby paints from a Model Tool company
and have my own small airbrush sprayer and compressor. If I was going to
use a spray can it would be Rustoleum brand. I have had very good luck over
the years with their paints-including their zinc chromate. You may choose to
sand between coats here as well-it will depend on just how good a finish you
want, and how many coats you choose to apply-based on application again.

4. PROTECTIVE COAT. I would suggest a coat or two of clear, semi-gloss, or
matte-depending on application and taste. If you are going to drill or letter
your panel, you should have done the drilling first-before any of this. Let-
tering should be applied after all painting if finished, but before the clear
coats. Remember, it is very important that the paint be allowed to thoroughly
'dry' between coats. This goes double for applying rub-on transfers-else
you'll lift paint when you apply the pressure. You should test your lettering
with your clear paint on a scrap to be certain the paint won't solvate the
lettering base and cause it to run/move. (In truth, it probably COULD-hence
the horizontal painting position of the panel. The thinner your clear coat
layers, the less likely they will float out of position.)

5. SAFETY CONSIDERATIONS. You would be amazed how much paint you sniff up
your nose when painting very much. Always wear some kind of protection. An
inexpensive allergy mask works pretty well for the money. You must always
paint only in a well ventilated area. Avoid dusty or drafty areas for
obvious finish reasons. Be VERY CAREFUL ABOUT FLAMES. there should be no
open flames anywhere in the room. Be very careful about solvents: they are
often highly flammable and usually known carcinogens. Be careful about
disposal: NEVER dispose of solvents in an ordinary kitchen drain or just
pour it into the soil around your house-it'll end up in your water table.

I hope this is helpful. You do not need to bake or otherwise speed up the
process. (It IS a fine way to do a beautiful wrinkle finish however-but
that's a different story.) Take your time, and you can do some really fine
work you'll be proud of. 72/73

-- 
Ed Tanton N4XY      EMAIL: n4xy@avana.net      TEL: (770)579-3933 Voice/MBX/FAX
189 Pioneer Trail, Marietta, GA  30068-3466

QRP-ARCI#7663 G-QRP#6779 OK-QRP#172 QRP-L#758 AdvRC#140 NORCAL#1779 NCDXF SEDXC Life Member: ARRL AMSAT IDRA INDEXA QCWA URL: Coming Soon "Think you can, think you can't: either way you're right!" Henry Ford


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