Corrosion on Alloy mast foot casting

[starboard]

The foot of my mast (25 years old) is an alloy casting. Over the past few years the black paint always flakes off due corrosion below. 2 years ago I sand blasted the casting, primed with aviation grade alloy primer then sprayed with hammerite black. This lasted 2 years but now showing signs of flacking again. This year I am thinking of sanblasting off old paint then polishing casting with good old "Solvol Autosol" Working on the principle the best cure for corrosion is as with all these French alloy yachts and "Ovni's leave the alloy uncoated.

Would welcome any views on subject and your experiances.

Good Luck

Paul.

 

[nedmin]

Ive got a steel cruiser and find that using Comma Wax Seal is excellent where you get a break ie where bolts go in to the steel work.I just spray around bolt then polish off.otherwise it is rust colour! Dont get Waxoil it is too thick to run in.I have also sprayed my trailer wheels with it. Could this be your answer?

 

[TigaWave]

I had to replace one on a 15 year old Sweden, it was so badly pitted I considered it weakened and didn't want it to collapse or fracture.

If its still in good condition you could try corrossion block or ACF-50 developed for the aviation industry after alloy wings were corroding on fighter aircraft based on carriers.

Theres a guy based at hamble airport importing it something or other aviation ltd. I've used it on alloy to alloy threads and it works.

 

[Birdseye]

Given the thorough job you did last time, I suspect that the corrosion returned either from the inside, or from dissimilar metals (eg rivets, cleats) poss even electrical leakage from wiring.

Masts do have a lifespan and 25 years must be getting near it. Before you do anything expensive, are you sure that you are not doing the equivalent of patching a Morris Minor? And are there obvious corrosion start points like rivets that need tackling

Assuming your happy with the state of the rest of the mast, I would be inclined to repeat what you did the previous time excepty using epoxy primer and twin pack poly topcoat. Then I would very liberally coat the inside of the mast at the mast foot level with Waxoyl.

As an alternative, remove the shoe and have it anodised. Cheaper than you think and much more effective against surface corrosion.

And Ovnis do have corrosion problems at the usual place where paint meets bare alloy. Thats why they have a tape all along the line where this happens. It seals the edge of the paint. Mind you I still fancy one.

 

[cliff]

Paul, You could do what I did with the mast step on the Jaguar - there is a Co near Dumfries that will prepare the casting and re anodise it (hard anodising) all for the sake of a few beer tokens - much superior to painted finishes but there again WTF do I know.

Just had a thought - what colour would you like it?

I'll look out the details and PM you
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"Artificial intelligence is no match for natural stupidity"

 

[starboard]

Thanks Cliff will seek more info on that. Got all frigging Winter to think. I see the Russian trawler crew back for weekend.......Vladivar has a present for you!!!!!

Paul.

 

[cliff]

just been down and "Ivor" tried to empty my wine cellar - silly boy!. I left him a few aspirin for tomorrow morning. I wish I had a camera to catch the pair of them swigging good malt straight from the bottle and washing it down with copious quantities of vino.

Still, went fishing after and caught breakfast - about a dozen nice mackerel /forums/images/graemlins/grin.gif
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"Artificial intelligence is no match for natural stupidity"