[sdiy] Baked on Enamel Finishes?

[Paul Higgins]

Finally, a topic I actually know something about!  I've been doing 
paint work for many years.

Tom Henry had a pretty good article in Electronic Musician years ago 
that outlined his basic approach to painting.  The process is actually 
pretty common-sense, and I've been using it for years (with a few 
modifications from the auto-painting industry).

1) Remove all contaminants like tape adhesive (from doing your panel 
markup) using your favorite solvent (e.g. MEK, lacquer thinner).

2) Do your surface prep.  This is where everyone usually goes wrong.  
Chemically prepare the surface or sand it using progressively finer 
grits of sandpaper.  I usually start with #80 and end at #220 with the 
primers I use (this is with an orbital sander).  YMMV--some people 
insist on ending with #320.  The chemical preps can be pretty nasty, 
especially for aluminum.  One of them (from DuPont) is a chromate 
conversion step, which I really don't recommend due to its high 
toxicity.  Instead, I suggest an etch primer (see step 4).

3) Vacuum off all sanding grit and clean again with solvent to remove 
any skin oils, etc.

4) Primer coat.  Aluminum in particular is challenging to paint, at 
least if you want the paint to stick and take any abuse.  I use a 
self-etching primer made by SEM.  You should be able to get it at any 
auto paint store.  Just stay away from some of the other products these 
stores carry, like the two-part urethanes (see next step).

5) Last step--the topcoat.  I would bet that the paint already on your 
panels is a primer if it looks like a flat enamel, and it can probably 
be topcoated with just a little scuffing (wet-sand with #320).  You can 
probably skip steps 1-4.

Most likely Polyfusion contracted out their paint work and an extremely 
tough industrial or auto paint was used, typically an epoxy or 
urethane.  Unfortunately, the hardeners in these paints, particularly 
urethane, tend to be extremely toxic.  People *have* died from being 
exposed to this stuff.  Steer clear unless you have the safety 
equipment (a complete air-supplied suit).  A charcoal-filter respirator 
is *not* good enough, no matter what anyone tells you.  (I still can't 
believe so many auto paint stores recommend this stuff to anyone who 
walks in the door!).  You probably won't ever be dealing with these 
paints as they require a spray gun, but I always warn people anyway.

What I find to be about 80% as good as industrial or auto paint is 
something you can find at any home store.  It's the "Hammered Finish" 
made by Rust-Oleum, and it comes in a few colors.  If you let it cure 
for a day or so and then bake it in an oven on the lowest setting 
(about 170 ºF) for an hour, it will become really hard and tough.  Of 
course, this assumes you want a slightly textured-looking finish.

It's too bad there aren't better paints available to hobbyists these 
days.  Most spray paints are total junk--you can scratch them with your 
fingernail.  That is definitely *not* the case with the Rust-Oleum 
hammered finish.  I remember there was a clearcoat years ago that was 
really great--a clear epoxy that came in a spray can.  They must have 
put in some kind of inhibitor so that it wouldn't cure in the can.  It 
evaporated when you painted and the epoxy then cured to a tile-like 
hardness.  It was like auto paint without any of the safety issues.  
Naturally, they discontinued it.

There's another hammered paint I'm thinking of--I believe it's called 
"Hammerite".  It's supposed to be pretty good, but it has a cure time 
of something like a week.  That's because there's something in it that 
slowly cross-links the finish, making it really tough.  I've never used 
it, though.  I was kinda put off by the long cure time.

Good luck with your project!  Hopefully some other list members will 
add to the discussion.

-PRH

On Sunday, Oct 23, 2005, at 17:55 US/Central, Tim Curtis wrote:

> Hopefully someone's been through this same thing here and can give me 
> some tips...
>
> I've got some original Polyfusion panels that were never painted or 
> silkscreened, which I'd like to use to finish off a few modules.
>
> It looks like a flat enamel paint, but I assume that it was "baked" or 
> something to improve it's durability.  (I don't know much about paints 
> at all)
>
> Can anyone give me any hints on how I could at least do the black 
> paint at home?
> Also, if anyone can recommend a place that could do inexpensive, 
> single color silkscreening, I'd love to hear about it.
>
> Thanks!
>
> Tim