Aluminum corrosion ???

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    Posted: 15 Jul 2014 at 6:35pm
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Have a painted Ali boat .its has corrosion over nearly all of the cabin area.
Have sanded it back and stripped it out best we can and will be useing a epoxy primer for the alloy.
But has any 1 else got any idea how to stop it coming back ? Any tricks or any thing??

Don't want painting it to be a waste of time

Any1 else done this before??
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Post Options Post Options   Likes (0) Likes(0)   Quote Quick silver Quote  Post ReplyReply Direct Link To This Post Posted: 15 Jul 2014 at 7:07pm
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Originally posted by 86mad 86mad wrote:


Have sanded it back and stripped it out best we can
Any1 else done this before??


Either it ALL gone or its not. Don't paint over little corrosion spots or it will be back.

Considered etch primer?


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Post Options Post Options   Likes (0) Likes(0)   Quote 86mad Quote  Post ReplyReply Direct Link To This Post Posted: 15 Jul 2014 at 7:12pm
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Have used 80grit sand paper.and a wire stripping wheel.from what I see it's all gone?
Thought about etch but think a 2pack epoxy has a bit more grunt.
Is there any way from stopping it popping up in other places later on?
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1) I hope that was a stainless wire wheel? If not, go over it again as you will have little remnants of steel in the alloy pores that will rust.
2) Alloy needs to be etch primed for most paints to take. The paints then go over the etch which binds them to the alloy. Not sure that epoxy straight onto alloy will last well, but haven't tried.
3) Keep your paintwork well waxed. The corrosion normally starts around paint edges and the edges of scratches etc. Keeping a good wax covering on it will usually help.
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Post Options Post Options   Likes (0) Likes(0)   Quote pjc Quote  Post ReplyReply Direct Link To This Post Posted: 15 Jul 2014 at 7:51pm
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I know a painted alloy boat looks nice but really you should not paint it,let alloy oxidise naturally as this is its defence.
The french do not paint alloy boats.except antifoul and that has to be a special paint.
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Post Options Post Options   Likes (0) Likes(0)   Quote 86mad Quote  Post ReplyReply Direct Link To This Post Posted: 15 Jul 2014 at 7:57pm
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Very good point about the wire wheel.will have to check it tomorow.
The corrosion has started around mainly stuff like rod holders, brackets,gps mounts,etc
But there is the odd patch in the middle of a panel unmarked will look in to using an etch
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Post Options Post Options   Likes (0) Likes(0)   Quote 86mad Quote  Post ReplyReply Direct Link To This Post Posted: 15 Jul 2014 at 7:59pm
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Originally posted by pjc pjc wrote:

I know a painted alloy boat looks nice but really you should not paint it,let alloy oxidise naturally as this is its defence.
The french do not paint alloy boats.except antifoul and that has to be a special paint.




I agree with this but brought the boat painted .so not to many options here haha
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Post Options Post Options   Likes (0) Likes(0)   Quote Tagit Quote  Post ReplyReply Direct Link To This Post Posted: 15 Jul 2014 at 10:19pm
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With your fittings (rod holders etc) either get the little top hat type things that go in the screw holes to electrically isolate the bolts, and use rubber isolaters under the fittings, or use the rubber isolaters and Duralac all the bolts. What you are observing is electrical corrosion and no amount of epoxy etc will stop it unless you can isolate all the dissimilar metals from the alloy.
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Post Options Post Options   Likes (0) Likes(0)   Quote cirrus Quote  Post ReplyReply Direct Link To This Post Posted: 15 Jul 2014 at 10:28pm
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Should unpainted aluminum that is developing the protective oxidation be waxed. If so what wax.


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Post Options Post Options   Likes (0) Likes(0)   Quote 86mad Quote  Post ReplyReply Direct Link To This Post Posted: 16 Jul 2014 at 6:39am
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Thanks tagit

Have heard this to .ill try all these things hopefully it works.
I know I'll never stop it .but I want the new paint to last as long as possible
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Post Options Post Options   Likes (0) Likes(0)   Quote the angler Quote  Post ReplyReply Direct Link To This Post Posted: 16 Jul 2014 at 6:54am
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I'm doing the same thing , sounds like it's all in the prep , I hate sanding it's like someone running there finger nails down a chalk board for me .
Have a look at a similar topic from couple months ago I got some good advice from spectrum .
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Post Options Post Options   Likes (0) Likes(0)   Quote Tagit Quote  Post ReplyReply Direct Link To This Post Posted: 16 Jul 2014 at 7:32am
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Originally posted by cirrus cirrus wrote:

Should unpainted aluminum that is developing the protective oxidation be waxed. If so what wax.


It might look nicer, but no need for corrosion protection. Waxing over paint just helps stop the salt get under the paint through all those little scratches that develop over time. Makes it look nicer as well!
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Post Options Post Options   Likes (0) Likes(0)   Quote Wide Load Quote  Post ReplyReply Direct Link To This Post Posted: 16 Jul 2014 at 8:45am
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Originally posted by Tagit Tagit wrote:

With your fittings (rod holders etc) either get the little top hat type things that go in the screw holes to electrically isolate the bolts, and use rubber isolaters under the fittings, or use the rubber isolaters and Duralac all the bolts. What you are observing is electrical corrosion and no amount of epoxy etc will stop it unless you can isolate all the dissimilar metals from the alloy.
http://www.anzor.co.nz/ureseal
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Post Options Post Options   Likes (0) Likes(0)   Quote 86mad Quote  Post ReplyReply Direct Link To This Post Posted: 16 Jul 2014 at 1:28pm
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Glad I'm not the only 1 with this problem...
Thanks for every1s input will be a big help
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Post Options Post Options   Likes (0) Likes(0)   Quote Busted! Quote  Post ReplyReply Direct Link To This Post Posted: 22 Aug 2014 at 8:57am
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I've found duralac on bolts to be an expensive waste of time.  The duralac strips off the bolt threads, so doesn't isolate.  Best to use isolator bushes made from acetal industrial plastic, doesn't absorb water and become conductive and the other way is full gaskets or isolation pads under everything.  Or better yet, install to be removed and cleaned once a year...

Duralac is good as a painted on finish under/between bearing blocks, winches, wear the load is high and you can't use isolation pads due to flex concerns. 

But. at the end of the day ali is ali and if you can't see it you can't clean it.  If you can't clean it it will corrode.  All it takes is moisture getting into a recess with a salt or mineral deposit (eg volcanic derived lakes and rivers) and you can get the white furry ali oxide buildup occurring.

If I built an ali boat, rather than buying one I would not be painting it.  I would just use a good automotive wax one a year and clean with wash and wax in the interim period...
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