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Old 26-10-2015, 19:59   #16
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Re: Removing Paint From Aluminum Hull

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Originally Posted by noelex 77 View Post
Painted aluminium is normally left a little rough to allow the paint to adhere. So you may have to polish the previously painted areas to match with the rest of the unpainted hull.
That might depend on what you consider rough. Scotch brite might be enough.
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Old 26-10-2015, 20:04   #17
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Re: Removing Paint From Aluminum Hull

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Originally Posted by colemj View Post
Probably a dumb question, but why does aluminum need a barrier coat? Unless this is the same meaning and function as a primer coat.

Mark
The Copper in bottom paint is a LOT more noble than Aluminum. So, without a good barrier coat, to keep the two electrically seperated, the hull becomes a big anode. AKA Bad JuJu. And the paint would eat the hull.

Aluminum is right next to Zinc on the galvanic scale. Meaning that it sucks at resisting corrosion, inherently. But it's got one thing going for it...

It oxidizes quickly (so fast that in theory a plane should melt in a rain storm), but said oxidation naturally forms a hard protective layer on it's surface. And said naturally protective oxidation layer is what makes it a decent material for boats (at least when using the right alloys of it).
That, & it's relatively light weight, being only 1.5 times as dense as fiberglass. Plus the whole toughness thing. And it's easy to work with/machine.

Anodizing (aluminum) is in essence, a magnified version of Aluminum's natural oxidation process. Only, when done properly, it's a super hard version of it, that's very resistant to corrosion (SIC).
So what people think of as a protective coating (anodizing), is just a very tough, protective, surface layer of rust which has been (artifically) electrochemically created on the surface of the material.
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Old 26-10-2015, 20:07   #18
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Re: Removing Paint From Aluminum Hull

Aluminum needs an anti-corrosion primer coating to help prevent corrosion and to assist in paint adhesion. if the aluminum is to be bare, a good polish will do the trick, but the polish needs to be repeated often, as Air Force mechanics can tell you.
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Old 26-10-2015, 20:23   #19
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Re: Removing Paint From Aluminum Hull

Aluminum oxide is seriously hard. Think grinding wheels and sand paper.
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Old 26-10-2015, 20:38   #20
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Re: Removing Paint From Aluminum Hull

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Originally Posted by UNCIVILIZED View Post
The Copper in bottom paint is a LOT more noble than Aluminum. So, without a good barrier coat, to keep the two electrically seperated, the hull becomes a big anode. AKA Bad JuJu. And the paint would eat the hull.

Who paints aluminum hulls with copper-based bottom paint?

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Old 26-10-2015, 20:42   #21
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Re: Removing Paint From Aluminum Hull

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Originally Posted by mramoo View Post
Aluminum needs an anti-corrosion primer coating to help prevent corrosion and to assist in paint adhesion. if the aluminum is to be bare, a good polish will do the trick, but the polish needs to be repeated often, as Air Force mechanics can tell you.

OK, I understand the primer part and misinterpreted the meaning of barrier coat in this context.

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Old 26-10-2015, 21:59   #22
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Re: Removing Paint From Aluminum Hull

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Who paints aluminum hulls with copper-based bottom paint?

Mark
Steve Dashew....

But it still seems mighty risky even with a seriously built-up barrier coat.

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Old 26-10-2015, 23:01   #23
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Re: Removing Paint From Aluminum Hull

Rent/contract soda blast.
I respect Dashew but copper -NEVER on aluminum even with super barrier coat.
Entirely problematic-way invite grief?


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Old 27-10-2015, 08:33   #24
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Re: Removing Paint From Aluminum Hull

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OK, I understand the primer part and misinterpreted the meaning of barrier coat in this context.

Mark
The Air Force used to like their aircraft to be shiny, Aluminum if left untreated will get a coat of oxide. This is very dull, so they would polish the aluminum.
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Old 06-11-2015, 09:43   #25
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Re: Removing Paint From Aluminum Hull

We use the Dustless Blasting system with mixes water with the sand or crushed glass, reducing heat and preventing warping. Personally I prefer to blast with sugar sand as its more forgiving on aluminum and removes the paint quite well leaving a nice surface ready to repaint. Unlike with soda blasting, using the sugar sand, you don't have to naturalize it before repainting.
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