Aluminum pitting or something else

[aghoti]

Hi,

I've come across something I can't place, I am hoping for some input. Basically its an Aluminum frame in a boat between the mast step, keel and chainplates opening up some pitting revealed a crumbling rock type substance.

http://ivila.net/dir/Photo 3-07-11 14 35 25.jpeg

http://ivila.net/dir/Photo 3-07-11 14 36 09.jpeg

http://ivila.net/dir/Photo 3-07-11 14 35 01.jpeg

http://ivila.net/dir/Photo 3-07-11 14 34 25.jpeg

The substance is hard but breaks down into a white crumbly powder, chalky to taste.

I am struggling to place it. Any ideas?

Alex,

 

[Ron]

If this is a marine environment, it is probably aluminum chlorides and hydroxides. From the staining, it appears to have some iron contamination.

 

[Compositepro]

In a marine environment all aluminum will eventually turn to white powder. That is why metallic aluminum is not found in nature.