On 6 Apr 2006 08:28:01 -0700, "larry"
wrote:

Can you explain what you mean by Clad coating?

Well... Aluminum is a whitish-gray material, not slick and shiny like
the sheet metal you buy.

OK

The sheetmetal product, and much plate stock,
is almost always 'clad-coated' and to my knowledge, not available any
other way.

Eh?

Clad coated?

Got a source for that info?

That shiny stuff is the 'clad' which is simply more
aluminum that has been pressed tightly to eliminate natural porosity.
Of course, the *process* has changed over the years but the result is
the same: shiny and slick sheetmetal.

This makes absolutely NO SENSE

Beneath the clad coating is "raw" aluminum. This has been the bugaboo
of corrosion problems among many. Raw aluminum is quite reactive to
air and water and protects itself with an oxide layer of white powder
(that also turns mysteriously black when you handle it -- kinda weird).
Depending on alloy, once the raw surface is exposed, the oxide layer
can go quite deep -- often deeper than the sheetstock IS.

Deeper than the sheetstock?

Like into thin air on the back side?

The clad
coating, while still aluminum, keeps corrsion at bay to a much greater
extent because it reacts far, far, slower than 'raw' aluminum. Once
this clad is gone, all bets are off.

The protective layer IS the oxide

Sanding or etching removes this coating pretty much every time. Once
removed, you're gonna hafta treat that surface pretty quickly with
aluminum specific coating (like alodine). Another poster quite rightly
pointed out that color is not supposed to be very 'deep'. "Well-done
fried chicken" brown is too deep. "Light Honey" brown might be more
appropriate. Gotta go, getting hungry alla sudden :-)


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