Aluminum Pitting (prep for paint) - Defender Source
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Old July 14th, 2014, 01:19 PM
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Aluminum Pitting (prep for paint)

So I'm prepping a hood for paint, and it's got a few spots of pitting where there was galvanic corrosion. Are there any tricks to clean the pits prior to paint. I don't think I want to sand until they're gone as it will remove a fair bit of material. I also don't want leave them as I'm sure they will work their way back through the paint eventually.

Is there a chemical stripper potentially?

Here is a pic of what it looks like.

Will
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Old July 14th, 2014, 01:22 PM
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It is critical that the aluminum is properly etched before paint. Acid etching primer will do the job.
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Old July 14th, 2014, 01:23 PM
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Yep got the proper etching primer. Just hoping to clean the pits out before I get to the primer stage.
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Old July 14th, 2014, 01:24 PM
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there is a thread on aluminum filler some where on here...
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Old July 14th, 2014, 02:03 PM
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Phosphoric acid and a toothbrush. Start with a mild solution as it will attack all the aluminum not just the oxide. Lye works too but is very aggressive on aluminum. Rinse rinse rinse!
After thorough drying (overnight is best) use filler to bring up the pits to the surface.
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Old July 14th, 2014, 03:50 PM
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Quote:
Originally Posted by o2batsea View Post
Phosphoric acid and a toothbrush. Start with a mild solution as it will attack all the aluminum not just the oxide. Lye works too but is very aggressive on aluminum. Rinse rinse rinse!
After thorough drying (overnight is best) use filler to bring up the pits to the surface.
This is what I would do other than I would use high build primer if the spots were shallow enough. I hate filler on aluminium.
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Old July 14th, 2014, 04:16 PM
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The problem I have had with high build primers is that depending on the paint formulation, it eats into the built up areas and you can see them in the finish coat.
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Old July 14th, 2014, 04:26 PM
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Quote:
Originally Posted by o2batsea View Post
Phosphoric acid and a toothbrush. Start with a mild solution as it will attack all the aluminum not just the oxide. Lye works too but is very aggressive on aluminum. Rinse rinse rinse!
After thorough drying (overnight is best) use filler to bring up the pits to the surface.
I'll track down some of the Phosphoric acid and give it a whirl. What type of store would you typically buy it from?

The spots are mainly on the inside of the hood and will be under the frame so getting them level isn't too much of a worry. Although I'm sure I will come across some other spots on the truck where it is more of a concern.

Thanks for the advice!
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Old July 14th, 2014, 05:59 PM
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Quote:
Originally Posted by Wilboro View Post
I'll track down some of the Phosphoric acid and give it a whirl. What type of store would you typically buy it from?
Home Depot under the name "Kleen Strip Prep and Etch". It is a milky clear bottle containing a green liquid - phosphoric acid.

$15 a gallon, which is half the price of Ospho.

-----

That said, the cheapest is to buy granules by the 50 lb bag, but that's not necessarily unless you plan on driving your truck into a pool of the stuff.

----

My opinion: Do not use filler on pits that shallow in depth. Use glazing putty instead.
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