How can I stop/slow aluminium corrosion?

[SDR]

Hello all,

I've noticed on various bits of window frame small patches of aluminium corrosion. Patches isn't really the correct word - it's very localised and presumably caused by the original coating being damaged or breaking down in some way at that point. The result is a pitted surface and powdery residue.

I'm sure this is just one of those things that happens to aluminium after it's been at sea for 11 years, but I'd quite like to do something to either stop the corrosion and stabilise the surface, or at least minimise the rate of progression.

The aluminium is... aluminium-coloured(!), not painted, and I don't want to get into serious dismantling of screens and what-not, it's only a minor irritation at present. However if anyone can suggest treatments that might help control the problem I'd be grateful. Many thanks.

Steve

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[AndrewB]

If you are spotting this corrosion on the outside of your window frames the chances are it is a lot worse behind, particularly if the frames are attached with steel screws. It may be worth taking one off to inspect.

There is no great harm in leaving bare aluminium on the outside, though as you say it doesn't look good, with a rough, powdery surface. Behind the frame though, you may have a gooey corrosive mess.

There are several marine window refurbishers, who will re-anodise a frame, off the boat of course. A polyurethane paint job starting with epoxy primer will last for many years. Or you could plan to buy new windows as they get worse, but they are not cheap.

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[Birdseye]

aluminium is almost as un - noble as zinc, so if it is in contact with stainless or any other steel it will preferentially corrode. if it is just on its own in a marine atmosphere, it seems to form a thicker oxide skin and do no more than go dull.

you might try removing the fasteners concerned (if you can!) and then painting the aluminium (can be clear paint as in laquer). re fix, bedding the fasteners in duralac.

to be honest, its likely to be a forth bridge job. the only longer term cure would be to remove and re-anodise, then bedding in the screws as above.

even with two coats of epoxy primer and then two coats of 2 pack poly topcoat, i find i have to touch up my catamaran drive leg every two or three years. and people recommend aluminium boats!

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[paintercolin]

Agree with birdseye. I work as painter in NL. Currently helping to paint 76m superyacht with alloy superstructure. Any join between alloy and steel is a nightmare. The alloy dissolves to a white powder then gel. I have seen alloy held together by paint. Clean the corroded areas and paint asap after prep. Don't touch up with 2 pack epoxy if the existing paint scheme is 1 pack. Don't use steel wire brush to clean - you'll embed steel in softer alloy and get more corrosion. If you take out window, use insulating compound and plastic washers and sleeves if possible. Paint the inside of any hole if you can. Anodising is great is you don't mind the look. You could also investigate powder coating - this is used on architectural window frames

Alloy is fine on its own. We painted Gerald Dijkstra's (famous designer) personal boat - he left hull as plain alloy. It goes a mottled dull grey. Maybe doesn't look that great but you'll never worry about painting or polishing again.

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[dickh]

Almost certainly your frame is secured with Stainless Interscrews, and after a while the aluminium corrodes as mentioned earlier. If you remove the frames, you will probably find worse hidden corrosion. The screws should have been coated with Duraloc to prevent corrosion, but I don't think this is done during the building. The only way is to remove the frame, clean up, replacing ant Interscrews and making sure you use Duraloc between the Aluminium and the screws, and plenty of mastic of course. Or put in new windows!

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I'd rather be sailing... /forums/images/icons/smile.gif

 

[Birdseye]

Duralac works brilliantly. I dont know how or why, but its one of a relatively short list of products that "does what it says on the tin"

I use it on my outdrive leg which is repeatedly immersed in salt water, and stailess fasteners come undone without problem after years

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