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