Old Aluminum light housing / cleats - Corroded

[mikebikeboy]

I am working on the mask of a boat I recently bought. The aluminum light fixtures and aluminum cleats on the mast all look like this:



Is this a problem? There's old black paint flaking off, and underneath is all this white chalky stuf I don't know what it is. It's not salt because this boat has never seen a grain of salt in it's life.

Should I sand it and repaint with some kind of exterior oil paint?

[roverhi]

The white chalky stuff is aluminum oxide/aluminum rust. The oxidation actually protects the underlying aluminum from further erosion by oxidation. You can try and clean up the painted section and repaint but follow the directions for painting aluminum very carefully. Believe most systems call for removing all flaking to bright metal then cleaning with an acid etching compound to get at the ingrained oxidation. Any bare aluminum I install, like backing plates, is first sanded and then sprayed both sides with zinc chromate primer. That has really helped in keeping the oxidation from appearing.

Corrosion is only a problem if it has eaten so much of the metal that it is no longer structurally sound. The piece you pictured looks to be okay from what I can see.

[mikebikeboy]

thanks for the info roverhi

[Cheechako]

I'd probably replace those, but if you wish to restore have them grit blasted. Any finish may degrade on aluminum even with all the things done right, but you can choose to leave them bare or paint immediately after blasting. Like Roverhi said Zinc Chromate primer is touted for that. I dont know how good the over-the-counter stuff is though. I painted something with it once and used the same brand top coat. It stayed gummy for a long time for some reason.