[R-390] Painting Notes and Parts

[Al Parker]

Hi all,
    I spent my former life in the aluminum industry, learned a lot, forgot a
lot, sure didn't learn it all.  But, back when I was in some plants that did
"coating", or painting, strip/sheet for various things, usually at speeds of
several 100fpm & continuously, I learned that the various paints/coatings
used like to have a slightly acidic surface upon which to attach, and
dislike a slightly caustic surface, which good be left by soapy cleaners.
Phoshphoric acid was the "preferred" stuff, & was used in various
combinations with other stuff, including chromium, to provide a "conversion
coating" for future painting/coating.  Phosphoric was/is pretty nasty stuff,
and the chromium solution was/is tough to treat for proper disposal.  Other
safer alternatives were developed, and a conversion coating as such is not
always developed or reqd.  (If Dr. Ornitz frequents this list I'm sure he
could elaborate much better than I.)
    Anyhow, to make a long story useful, the metal surface, especially
aluminum,  should be somehow acidified before priming.  I've found the
easiest way to do this is with diluted household vinegar, a few ounces to a
pint of water.  Just swab it on after the surface has been cleaned.  Let it
run off & dry naturally.  I've even used the mixture when wet sanding
between coats, just 'cuz it was still sitting there.  Figured it couldn't
hurt, might help.  I can't think of any flaking or peeling problems with
anything I've treated this way over the yrs.  I guess the dilute acid
actually does slightly etch the surface, and provides a bit of tooth.
    All FWIW & YMMV
73,
Al, W8UT
New Bern, NC
BoatAnchors appreciated here
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----- Original Message -----
From: "Barry Hauser" <barry@hausernet.com>>
> Before repainting, you should use a prep solution, such as Alum-Prep (they
> say) but I couldn't find that nearby, so used a I used self-etching
primer.
> Gotta put it on very sparingly or you'll fill up the "engravings" too
much.
> (Then it becomes pointed stick time again.)