Cast aluminum gooseneck & mast step

[Mike Rodriguez]

Hi all, My gooseneck and mast step is cast aluminum that was painted black at one time. It now has sort of a white chalky gangrenous aspect to it. Would it be okay to sand and repaint it or is this chalky substance an indication of imminent failure?

Thanks in advance

[tartansailor]

The white fluff; to state the obvious, is corrosion residue. Bare Aluminum (from an adhesives chemist's perspective) is difficult to get a satisfactory bond without the use of an esoteric (read expensive) urethane. The recommendation is to have the bare aluminum phosphate treated, then coated with aircraft quality paint. Than you can forget that problem for a while.
Dick

[Oswego John]

Hi Mike,

Does it only form where the paint has worn off?

Without seeing it, it sounds to me like a classic case of aluminum oxide. Some fancy names for it are alumina and corundum.

It is hard to dissolve chemically. Either acids or alkalis can remove it. I'm not familiar with using phosphates (phosphoric acid maybe ?) as Tartansailor mentions, sorry.

I find that the easiest way to treat it is to remove it with medium grit sandpaper or wet and dry paper. Don't use a fine grit, you want the bare aluminum to have "tooth" when you prime it with Zinc Chromate primer which is available in most paint stores

Top coat it any color you want. I've used plain old Rustoleum and find it as good as most of the rest.

I forgot to mention that after it is down to bare metal, give it a good inspection for any possible faults or weaknesses.

Good luck,
O J

[bottomscraper]

I had a hard time finding zinc chromate primer at the local hardware and paint stores two years ago. I finally did find some at a boating store made by Tempo for outboard motor painting. I used the 5605 green zinc chromate for our boom. I believe they now say that it is for "professional use only".

Tempo Catalog

[Oswego John]

Hi Rich,

Yes, I guess you're right. Z. C .isn't as easy to find as it used to be. For many years I used to buy it in quart cans from Ace Home Supply. The last time I went to buy Z.C. from them, they told me that the average homeowner doesn't buy it. If I wanted them to order some for me, I'd have to order a case, 4 quarts They didn't want to get stuck with the other 3 quarts.

I was told that Sherwin Williams paint store might have it in stock. If not, I might be able to order 1 quart.

Zinc Chromate and Gulden's mustard have a lot in common. Old man Gulden made his fortune, not on the mustard that the country used, but on the mustard that was wasted. Gulden's odd shaped bottle was designed for a purpose.

The last time I bought Z.C. primer, I got some from a metal fabricating shop. They buy it in bulk. I buy it in small quantities so it won't be wasted.

FWIW, I try to use red iron oxide primer on ferrous metals and C.Z. primer on non ferrous metals.

Take care,
O J

[Mike Rodriguez]

Dick, Rich & O J, Thanks for the info. I was thinking that maybe the aluminum was becoming brittle. I should be able to find the Zinc Chromate here.
Rich, I read your post about Sta-lock fittings. WOW!!
O. J., more mustard.


Regards

[Ron M.]

My spars must have known your spars. There was corrosion at almost every screw and fitting;white residue and paint bubbles.I sanded off all paint and then,(most important) used Interlux dewaxer - I think 202 -
and the "2 rag method" to get the metal as clean as possible.Then continued with resanding w/120grit another solvent cleaning and application of zinc chromate wash,(I stayed with Interlux products).
Next was 2 coats of primer - Primekote- I beleive, and 3 coats of 2 part polyurethane paint - platinum grey.Has held up well and looks good if not a bit too glossey,(there is a matting agent available).
I may not have the names and #'s correct but If you stay with a product and use it's recommended system, follow all instructions I think you acheive better result instead of mixing different brands.
The hardest part was holding the 36' mast like an ear of corn so I could spray it with one shot,rotate it and spray it again.Good luck.
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[Ron M.]

I forgot to add Mike.
Merritt Supply in Fla. has a good selection of paint systems.
Shipping is expensive,(hazardous material)but quick - at least to Ma.
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[Mark Yashinsky]

did you remove them (if possible) and after painting, use some galvanic corrision eliminator on them when reinstalling? If not, guess whats going to happen between the aluminum spar and stainless steel screws (and the paint that gets in the way)?

[Ron M.]

Mark,
Every fitting and screw was removed.In an effort to avoid a repeat of this corrosion problem a Locktite product was used when reinstalling the cleaned hardware.It did take some time-there are a lot of screws but so far so good(2 years).RM
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