Aluminium Pitting - best way to neutralise?

Gubbo

Gubbo

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www.sailpast.co.uk
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I'm taking on a project aluminium hull that seems generally sound, but there is some pitting corrosion on one panel that I need to deal with.

This has been subjected to stagnant bilge water for a couple of years and there are numerous pits appearing.

The one in the photo is the largest and I have measured its depth with a micrometer at 1.1mm. The panel is 5mm thick so I'm confident that there's plenty of metal left, but of course want to "stop the rot"

My research suggests I need to clean off the oxidation with acid, but suggested types vary from vinegar and coca-cola through to specialist aircraft restoration chemicals.

I'm in the UK and so need a chemical that is available to me as a retail customer. What have you used with success? What treatment would you recommend after acid cleaning? Or should I try a different technique altogether?
 
Aluprep will clean it for you.
I don't believe you should do anything to cover it up. Aluminium produces its own oxide to protect itself. The acid encourages a strong oxide to form.
Coating it with anything other than an oil will encourage poultice corrosion which you definitely don't want.
Keep the bilge clean. Remove all noble metals that could come into contact with the aluminium .... copper, lead, stainless steel, etc.. Make sure there are no stray electrical currents.
It looks like the hull plate has had another plate welded over the top. This is very bad practice and could lead to structural problems. I suggest you get the advice of a surveyor experienced in aluminium vessels.
 
Gubbo said:
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I'm in the UK and so need a chemical that is available to me as a retail customer. What have you used with success? What treatment would you recommend after acid cleaning? Or should I try a different technique altogether?
Click to expand...

Try a decent paint wholesaler ( not B & Q etc)
They sell acid etching solvent for cleaning galvanised surfaces etc prior to painting
I expect it would etch aluminium as well
They would then advise on correct paint
You may have to buy a litre but that is not a big deal

I would try contacting Aczo paints & asking to speak to a paint rep for your area
They would then prepare a spec FOC
In the construction industry they do it all the time so I expect they would help
may even come & have a look for a drink !!!
 
Many thanks for your replies.

I haven't been able to find an obvious supplier for the alodyne aircraft products yet, but have found Machine Mart do a retail product called simply Aluminium Cleaner that contains Phosphoric Acid. Would this be a starting point?

Once I get the boat closer to home, I'll get a welder to take a look with a view to grinding and filling the pits for a permanent job (there are only about a dozen of the type pictured). Hopefully the chemical treatment will deal with the minor ones and keep things in check.
 
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