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ErikFinn · 11-02-2017, 20:57

I'm starting a new thread hoping to get an answer to this specific question:

Is it ok to polish over aluminum oxide leaving the oxide layer under the polish, or not?

Would the oxide layer under the polish layer cause problems or would it be just ok and protecting the good aluminum?

This would be on an aluminum windlass case, using Noxon 7 Metal Polish.

The whitish spots on the photo are what I gather aluminum oxide, not salt, as they are so bloody hard to remove, so if it is ok I would just like to polish over the spots and be done with it..

Alan Mighty · 11-02-2017, 23:28

Quote:

Originally Posted by ErikFinn

The whitish spots on the photo are what I gather aluminum oxide, not salt, as they are so bloody hard to remove, so if it is ok I would just like to polish over the spots and be done with it..

A surface layer of aluminium oxide forms over aluminium metal exposed to air. Aluminium oxide is transparent and the layer is thin. The shiny metallic surface you think is aluminium is aluminium oxide.

Your 'whitish spots' are probably accumulations of poultice. As in poultice corrosion of aluminium.

The poultice is a combination of hydrated aluminium hydroxide and aluminium oxide.

And yes, it is very hard: hard to remove and hard in terms of Moh's scale of hardness.

What is your objective in applying a metal polish?

What is the nature of the polish: is it just an abrasive? or is it a wax?

If it is a wax, the next question is whether you should trap crystalline hydrated aluminium hydroxide on the surface of an aluminium fitting and under a layer of wax?

Or would it be better to remove the poultice and to anodize the fitting?

Or to remove the poultice, prime the fitting, and then paint it?

**a64pilot** · 12-02-2017, 05:37

Want is the objective? I assume to make it look nicer as opposed to prevent corrosion?
Coming from an aircraft background I don't believe you will reduce its life much if any at all by polishing it, but I would consider bead blasting, alodining it and having it powder coated. That I believe would look the best and give longer lasting protection. The powder coat will eventually fail though, but hopefully not for ten years or so

ErikFinn · 13-02-2017, 00:49

Thank you for your kind reply Alan, I'm answering your questions below in red:

Now that I know the whitish spots are "Poultice" I guess the question then becomes: Is it OK to polish (and wax) over aluminum poultice or not..

Quote:

Originally Posted by Alan Mighty

What is your objective in applying a metal polish?
I would just like to give the aluminum surface some protection against corrosion and the elements but I don't want to go through a painting process, and I would like to get the windlass cover to look a bit more tidy, not like showroom tidy, but just enough to get rid of the dirt and grime you can see on my photo here (post #1), but not make any detrimental error by trapping the poultice under a layer of polish/wax (if that would indeed be an error):
http://www.cruisersforum.com/forums/...ml#post2093935

What is the nature of the polish: is it just an abrasive? or is it a wax?
I'm not very familiar with this product, I just happen to have it aboard, I've used it to SS, and the sticker says "Aluminum" (among other metals). I'm not familiar how to manage aluminum, I just know its different than iron and SS...

You think it would be ok to use this Noxon 7 (Photo attached) on the windlass case for trying to make it look a bit prettier and to protect it from the elements, applied over the poultice?

Or should I also wax it with something like a car wax? I guess I should be asking if this Noxon leaves a protective layer on the surface or do I need something like an ordinary car wax for the protection?

If it is a wax, the next question is whether you should trap crystalline hydrated aluminium hydroxide on the surface of an aluminium fitting and under a layer of wax?
This is what I'm trying to find out..

Or would it be better to remove the poultice and to anodize the fitting?
Is there an easy way to remove the poultice then? I could remove most of the poultice using a Dremel but that wouldn't guarantee I was able to remove 100% of it. And that would remove some good aluminum also in the process..
For now I'd be happy to put in minimum effort unless it means the case will be ruined after 2 or 3 years. Finding an anodizer here might be challenging also.

Or to remove the poultice, prime the fitting, and then paint it?
I don't wan't to go through the hazzle of painting because I've read folks' paintjobs are usually not long lasting on windlasses..

ErikFinn · 13-02-2017, 00:57

Quote:

Originally Posted by a64pilot

Want is the objective? I assume to make it look nicer as opposed to prevent corrosion?
Coming from an aircraft background I don't believe you will reduce its life much if any at all by polishing it, but I would consider bead blasting, alodining it and having it powder coated. That I believe would look the best and give longer lasting protection. The powder coat will eventually fail though, but hopefully not for ten years or so

Hi a64, objective is to just to tidy the lass a bit and hopefully slow corrosion.. I would not like to go through a painting process , powder coater might be difficult to find here, and heck, let's not beat around the bush, I'm lazy, hehe. You reckon polishing and or waxing over the "poultice" would be a mistake? Do people polish their aluminum windlasses? Do people wax them?

Alan Mighty · 13-02-2017, 02:16

1. Remove the white deposits

The white deposits are either or both hydrated crystals of aluminium hydroxide from poultice corrosion or hydrated crystals of aluminium oxide from pitting corrosion.

If windlass case was originally painted, I would guess that the problem started with a break in the paint that allowed salt spray to invade under the paint. The invasion of salty air under paint first causes production of aluminium oxide powder. The volume of Al2O3 powder lifts more of the paint off the metal surface - a process of pitting corrosion that that just spreads. Salt spray then feeds water and chlorine ions into the powder under the paint, keeping it moist and developing poultice corrosion with the formation of hydrated crystals of Aluminium Hydroxide Al(OH)3.nH2O.

Once the poultice corrosion has formed, as shown by those white deposits, further exposure to salt spray can continue the corrosion. Cynics and pessimists say it only ends when the aluminium has turned into dirt. So it is probably important for you to remove those tiny poultice deposits, because they are likely to get wet with rain and salt spray if not seawater again.

The easy way to remove the poultice is garnet blasting, i.e. sandblasting with garnet powder. Garnet sand as a hardness, on Mohs scale, of about 7. A skilled operator would take only a minute to blast your small poultice deposits (but would have to charge for setting up).

If your poultice deposits are limited to the few in your photo, then work with a Dremel tool should do the job.

2. Protection of aluminium after garnet blasting

A. If your windlass case is small and transportable, the easy way to protect it for the future is to anodize it. The simplest and cheapest is Type II anodizing, done at room temperature. More expensive is what is called hardcoat or Type III anodizing, done in refrigerated acid.

B. Alternatives to anodizing are to coat it again. The usual routine is to coat with a zinc chromate primer (the big international brand name is Alodine), then a high-build primer to fair the surface, followed by a two-pack paint. As a64 notes, a small piece such as your windlass case could be powdercoated less expensively.

3. Maintaining anodised or painted aluminium

Maintenance of both is much the same - aluminium does fine if it is kept dry and clean. Any break of its protective surface (natural aluminium oxide, anodizing, 2-pack linear polyurethane, powder coat) in the presence of salt spray or salt water will lead to pitting corrosion. Anything that allows salt water to sit on the aluminium (dirt, anything that stays moist) will lead to poultice corrosion. So keeping aluminium clean and dry is important. Stopping breaks, abrasion, etc to the protective coating is important - but not easy for the housing of a windlass that will get some abuse through routine use. Anodizing can exceed the abrasion resistance of paint and powder coating.

Manufactures make to market demand. That means you can do a better job of bedding (with a non-hygroscopic sealant) all joints, fittings, and fixing (bolts, screws) that touch your windlass case. And make sure that stainless steel fixings are coated with suitable isolating substance (e.g. a barium chloride paste such as Duralac, or one of the Tefgel Tekgel isolating gels)

4. Getting the jobs done

Your profile suggests you are in Thailand/Malaysia. I am most familiar with Malaysia and Singapore; I've only cruised the coast of Thailand from Satun to Phuket.

You should have little problem finding firms to do garnet sandblasting and anodising in Malaysia or Singapore. Any of the major cities in Malaysia have firms that will do careful garnet sandblasting. In KL, for example, an internet search will find you a business that does careful garnet blasting for people whose hobby is rebuilding classic cars. I'd guess that the boatyards in Penang, Pangkor, Singapore etc could point you to both garnet blasters and anodisers.

I know hardware/DIY shops in Penang that sell grinding bits for Dremel (and similar) tools that likely would remove a couple of poultice deposits. I'm sure you can find such shops anywhere from Phuket to Singapore.

I know one cruising couple who, while in Singapore, built a new aluminium mast (about 14 metre) for their yacht. They wanted to have it anodized. None of the Singapore anodisers had an acid bath that was big enough to accommodate a 14 m mast. So the couple built their own bath in the anodizing firm's yard. Last I heard from them, their effort was worth it.

**a64pilot** · 13-02-2017, 05:11

Alodine is actually a two part chemical conversion process known as Chromate conversion.
Look up Alodine 1201 to see, it can be brushed on. It is not a paint, it chemically bonds to the aluminum, aircraft that are exposed to corrosive conditions like seaplanes should be alodined for example.
Alodine has been around for a LONG time, nothing new
However my opinion is if you polish it, it won't "hurt" it nor will it appreciably accelerate corrosion, it may in fact slow it.

Murrayk · 13-02-2017, 10:47

A product that is used widely here is 'Nyalic' which is like a varnish which I think will do your job well.

Cheechako · 13-02-2017, 10:55

I don't see a problem with polishing over that hard corrosion. Not sure it will last long though. Even hard waxing a hull for instance doesn't last long at all.

Dave22q · 13-02-2017, 15:35

Unless you place a very low value on your time, I would apply any polish that looks good. Removal of the spots sounds a little purist to me. I suspect the winch motor will fail long before the casing; 5 years, 10? I suspect you can find a lot more rewarding things to do. When you do replace it spend a little more and go stainless steel but that will eventually corrode as well.

captlloyd · 13-02-2017, 18:01

You have a rough casting there, either that was how it was cast, or it may be just pitted. To make it look nice like shiny polished aluminum nice you would have to take a grinding tool to it to get rid of the roughness, then keep working it down to a polish. Lots of work. And then it must be maintained. The easiest way to make it look good is to paint it.popcorn: