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Anti corrosive barrier
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English Dave View Drop Down
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Posts: 682 		Post Options Post Options   Quote English Dave Quote  Post ReplyReply Direct Link To This Post Topic: Anti corrosive barrier
    Posted: 13 May 09 at 5:05pm

I need to squeeze a thin strip of stainless in between an existing stainless steel fitting and my aluminium mast. Normally I would throw on a load of Duralac and be done. However, I cannot fully remove the fitting so I will have slide the steel strip into place. This makes applying the Duralac (and keeping it on) more difficult.

I have been told that if you chop up a 2litre milk bottle, the plastic will do just as well as the duralac. Certainly easier to slide in alongside the steel strip (it's a shroud plate but I'm not using it as this - it may appear in "Pimp" in a few weeks.)

Purists may say stick to the Duralac but  wonder if anyone else has experience of the milk bottle technique?
English Dave
Ballyholme Yacht Club

(You'd think I'd be better at it by now)

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alstorer View Drop Down
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Posts: 2899 		Post Options Post Options   Quote alstorer Quote  Post ReplyReply Direct Link To This Post Posted: 13 May 09 at 6:11pm
hmm. It'll certainly stop a galvanic cell setting up when merely damp, but water will still get to both metal and surfaces, and when properly wet all the way around. The Durlac doesn't just act as a spacer keeping the two apart, but as a barrier coating helping stopping water getting in.

It'll kindof work, certainly better than the two pieces being in contact, but there's a chance you're still creating a location for hidden corosion. Do you want to take the risk or not?
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didlydon View Drop Down
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Posts: 280 		Post Options Post Options   Quote didlydon Quote  Post ReplyReply Direct Link To This Post Posted: 18 May 09 at 3:18pm
So, excuse me for asking what might appear an obvious question - I'm not familiar with this. Do you apply this Duralac to anything stainless where it comes into contact with an ally mast or boom? Is it like a grease or mastic that goes between fittings like kicker straps & eyes for blocks & things, thus preventing an electrolytic reaction? 
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laser193713 View Drop Down
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Posts: 889 		Post Options Post Options   Quote laser193713 Quote  Post ReplyReply Direct Link To This Post Posted: 20 May 09 at 10:34am
Originally posted by English Dave

 it may appear in "Pimp" in a few weeks.)

You are breaking the most important rule here!

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Alistair426 View Drop Down
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Posts: 201 		Post Options Post Options   Quote Alistair426 Quote  Post ReplyReply Direct Link To This Post Posted: 21 May 09 at 4:24pm

Didlydon,

Duralac is a yellow paste which comes in a tube and gets everywhere when you use it...normally because I always seem to have to bolt fiddly things to masts. It's not just for stainless v ali contact; I was advised to use it when replacing fittings on a carbon mast as well.
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JimC View Drop Down
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Posts: 6660 		Post Options Post Options   Quote JimC Quote  Post ReplyReply Direct Link To This Post Posted: 21 May 09 at 5:57pm
I'd use duralac. By all means use your bit of plastic milk container to smear duralac into the gap though.

And yes, if anything its *more* important to use it on carbon spars than on aluminium.
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didlydon View Drop Down
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Posts: 280 		Post Options Post Options   Quote didlydon Quote  Post ReplyReply Direct Link To This Post Posted: 21 May 09 at 10:25pm
Ah.... Cheers Alex. I understand now. Thanx for the reply.. I guess I should've used it when I fitted a new kicker eye to my mast.....
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Granite View Drop Down
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Posts: 476 		Post Options Post Options   Quote Granite Quote  Post ReplyReply Direct Link To This Post Posted: 22 May 09 at 2:54pm
Duralac is zinc chromate paste and acts as a sacrificial anode.
 
With Aluminium and stainless the ali corrodes. With Carbon and pretty much any metal the metal corodes. If  the corrosion products cause the metal to expand then the carbon can get damaged, like putting an ali tube in a carbon mast (Old RS600 masts)

You want to avoid getting it onto your skin as it is quite nasty, it is also a pain to wash out of clothes.
If it doesn't break it's too heavy; if it does it wasn't built right
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timeintheboat View Drop Down
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Posts: 615 		Post Options Post Options   Quote timeintheboat Quote  Post ReplyReply Direct Link To This Post Posted: 22 May 09 at 3:58pm
A job for me later this summer then as I replaced all of the load bearing (and loose in some cases) rivets on one of ali masts with A2 stainless steel bolts. I've also discovered that apparently I should have used A4 stainless and not A2 (is there a big difference?) and err no Dualac.

Does it survive exposure to the elements and the occasional dunking?
Like some other things - sailing is more enjoyable when you do it with someone else
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Alistair426 View Drop Down
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Posts: 201 		Post Options Post Options   Quote Alistair426 Quote  Post ReplyReply Direct Link To This Post Posted: 22 May 09 at 6:04pm

A2 stainless will survive in the short-term, provided you give it a sloosh down with fresh water on a fairly regular basis. You might start to get a bit of discolouration but that, in the, again, short-term, shouldn't present a problem. Looking at the state of a lot of the fastenings on several SMODs, it is clear that their suppliers are more than happy to use A2 rather than the significantly more expensive A4.

But then again....there are different qualities of A4 stainless out there .

 



Edited by Alistair426
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