Painting weathered, cast parts?

Cast alum. (maybe magnesium) brake caliper. Original paint is chipped off in places, and metal looks oxidized.
How to best prepare this metal? A good scrubbing and rinsing, of course.
Light sanding, too. Then a good primer, thorough dry, and one or more top coats (complete dry between).
How important is it to sand *every* crevice? Am I compromising the entire paint job if I can't get these tiny corners?
And regarding product: is just enamel OK? The calipers are basically sand- (and gravel-) blasted all day long. Is there a better spray product (powder coating not an option) than hardware store enamel? Which primer to use?
Thanks.
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Confirmed with manufacturer that the calipers are made from forged aluminum.
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notme wrote:

Bead or sand blasting is ideal prep. Plastikote and others make caliper paint in several colors. High heat gloss, tolerant of brake fluid I would think
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Other than blasting, is it possible to do a good prep job with emery paper or such? Is it critical to get every crevice?

Prime first? Use a Plastikote primer?
Thanks.
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DaveC wrote:

Maybe not critical, but close. consider wire brush. Wherever you don't clean is where the paint will fail.

I doubt it, but I don't have a can here. I would bet it wants to be sprayed directly on the base metal.
OOOPS!
Incompatible Surfaces
* Aluminum (Limited Adhesion).
That's it, no more suggestions
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mattathayde had written this in response to http://polytechforum.com/metalworking/painting-weathered-cast-parts-197097-.htm :
------------------------------------- DaveC wrote:

there are a lot of break caliper paints out there in many colors so you should find one that fits your taste (i would say follow directions as to what primer/prep). as to prep if you cant sand blast i would clean as best you can and lightly sand then put them in a bucket with a lid and fine sand and either shake, roll down a hill a few times, or put in the back of another vehicle and drive is stop and go traffic for a few days
-matt
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This can be an issue because most of the time you do not know the cause of the corrosion and that cause, whatever it is, will be in the pits. Here is an example I had a cast aluminum base from a pedestal that was badly corroded. I faced this base leaving just a few remaining pits. I then placed the base on a new, never exposed to weather aluminum plate for 24 hrs. After returning and lifting the base, the new plate was corroding in the same location of the remaining pits on the base.. This base had been exposed to salt water very briefly and was the cause of this corrosion. I then washed the base with white vinegar and replaced the base again on another fresh plate. One day later, no corrosion. Salt reacts with aluminum very rapidly if not well anodized. So the lesson is that if the cause of this corrosion is not neutralized before painting, the corrosion will continue and the paint system, whatever it is, will fail. I think it is safe to assume that your observed corrosion could be caused by road salt. Please consider treating the casting with vinegar after thorough cleaning. Wash again, dry the casting and use an etching primer before final color.
This tip was the result of a discussion I had with a professional powder coater who stated that very often corroded aluminum parts, even after thorough bead blasting had been done, the fresh powder coating failed. I believe I have discovered why. Now the powdercoater routinely washes corroded aluminum pieces after beadblasting with vinegar as insurance and has not had a failure since. Steve

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Steve Lusardi wrote:

Vinegar is a neutralizer for salt? Anybody know what the chemistry is?
Good to know, BTW. Thanks.
Bob
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Bob, I assumed that salt is a base and to neutralize it, the application of an acid would be in order. As vinegar is a mild form of acetic acid, I gave it a try. It has appeared to work. Steve

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"Steve Lusardi" wrote: I assumed that salt is a base and to neutralize it, the application of an acid would be in order. As vinegar is a mild form of

^^^^^^^^^^^^^^^^^^^^ Salt is not a base. Salts are the reaction products of acids and bases, and are neutral. If vinegaqr worked, it ios probably becaquse it is a solvent for the corrosion that was on the metal. (Table salt, NaCl, is the reaction product of HCl and NaOH.)
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On Tue, 1 Sep 2009 20:51:13 -0700, Steve Lusardi wrote

Thanks very much, Steve, for sharing that experience. Very helpful. I get to learn from your experimentation. Which likely means success the first time for me!
Thanks again, Dave
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DaveC wrote:

Caustic soda (drain cleaner )is a good paint stripper , but it will attack aluminium and completely dissolve it if left in the solution too long. I have used it to strip paint from parts for my power hacksaw restoration it removed 40 years of layered repaints from the parts very quickly. Some of the parts were aluminium and I had to watch them very closely , as soon as the paint has been removed you need to wash them with clean water , the paint will just wash off.
I would plug any holes and galleries that you don't want the solution to get into.
--
Kevin (Bluey)
"I'm not young enough to know everything."
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I would bead blast, mask, prime with an etching primer (check with FinshMaster, I think I've been payint $16 per spray can) and then use the industrial Imron in the color of your choice. the urethane will hold up better to the blasting by road dust than an enamel or lacquer

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dont use sand blasting taht leave a rougher surface,... use a bead blaster.

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no one wrote:

i recently recoated my kitchen cabinet knobs. sand blasted them with AlO2 first, down to bare metal, then 2 coats of rustoleum appliance epoxy paint in a high gloss black (rattlecan). it filled the blasted surface completely (to where you can't tell it was blasted) and after curing at 200F for 4 hours, is very hard to scratch off.
follow can directions for recoating and cure times correctly.
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