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Old 06-27-2010, 06:51 PM   #1
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"Polishing" Aluminium?

Hi All,
I have a great Roskelly-Olsen fork davit on my Transome.
It is aluminum and painted white.* The paint is (of course) coming off and looks crappy.
I was wondering if I took the davit and had it brought down to bare metal and then "Polished" it (like they do for those shinny polished aluminium wheels) if it would hold up or would that just corrode too?
I know aluminum "oxidizes" in a marine environment, however those highly polished wheels seem to hold up well.
Would this solve my problem and keep me from having to re-paint it every few years?**

Your thoughts....
Steve
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Old 06-27-2010, 08:18 PM   #2
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"Polishing" Aluminium?

Aluminum that looks nice and dosn't seem to have any protection does * * ..it's anodized.Anodizing large parts is quite expensive. You get clear, or colors * * blue and gold are the most popular. I would suggest you powder coat it. It's like painting but they put colored powder on the surface and then bake at 400 degrees. The PC finnish is much much more durable than epoxy or poly whatever. Your davit manufacturer probably didn't anodize as the paint was a cheap way out of the finishing issue. To anodize you must remove all hardware that is not aluminum and to powder coat everything must be able to survive a 400 degree bake. If you can do neither I think you will be stuck with repainting unless you are willing to polish * ..and polish * ..and polish. Air Force 1 is polished but they have hundreds of E-2s to do it. I would be thinking 2 part epoxy but I'm not a painting expert. Someone else should weigh in.


Eric Henning


-- Edited by nomadwilly on Sunday 27th of June 2010 08:23:24 PM
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Old 06-28-2010, 08:11 PM   #3
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RE: "Polishing" Aluminium?

Powder coat will often fall off, just like paint. How do I know this?
Simplest is to repaint, using a good quality plastic (varathane) or one part polyurethane. Then when it falls off, you haen't a lot invested in it and it won't bother you so much as if you go to a lot of trouble for powder or anodizing, or polishing.
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Old 06-29-2010, 10:16 PM   #4
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RE: "Polishing" Aluminium?

Like any applied finnish * * ..some do it right and some do it quick and dirty.

Keith,
You say "how do I know this?"
Well..... how?


I worked for Production Plating in the seattle area and saw a lot of powder coating. Most of the work was commercial and had very few problems. Iv'e even seen propellers powder coated.


Eric
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Old 06-30-2010, 09:19 PM   #5
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RE: "Polishing" Aluminium?

Powder coating is an option.* I would love to hear of experiences with powder coating aluminum in a marine environment???

I'm just looking for low maintenance.

Thanks for the suggestions.

Steve
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Old 07-06-2010, 11:13 PM   #6
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RE: "Polishing" Aluminium?

From my experience, I would choose painting over polishing or powder coating. I have an aluminum mast and boom that I painted about ten years ago, and it has held up well. The secret is proper etching of the aluminum, and proper paint. The primer and paint must be compatible. I also have a transom mounted davit that I had built, and professionally powder coated. It is closer to the water, and does get more salt spray than the mast, and did have a failure in the coating in a couple areas. It's proximity to salt spray was undoubtedly part of the problem, but the initial failure of the coating was a huge disappointment. I guess it comes down solely to the simplicity of repairing a defect in the painted surface. Polishing is an option, but leads to the necessity for continued polishing. Forever.
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Old 07-07-2010, 03:52 AM   #7
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RE: "Polishing" Aluminium?

As an old rag bager I found the "secret" of the old aluminum masts.

Today masts are painted , but in the 60's 70's they were usually bare.

The material used to seal a concrete floor was the early mast builder sealer of choice .

Cheap and effective.
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Old 07-07-2010, 05:48 AM   #8
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RE: "Polishing" Aluminium?

Do you have to use any type of primer?
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Old 07-07-2010, 09:01 AM   #9
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RE: "Polishing" Aluminium?

Powder coating is fine, it's that wherever there is an attachment, the surface is compromised.
I have found that where the bolts go thru it inevetably exposes bare metal once that happens you will get rust or corrosion.
Unless you have aluminum bolts.
Two dissimmilar metals in a marine environment = corosion.

So if you powdercoat and can prevent any scratches it may work. Aluminum oxide is a natural coating that occurs with aluminum and oxygen. Once the surface is compromised the aluminum will oxidize and your powder coat will start to flake off off.
I have seen plastic washers or spacers placed between the metals. It is when you tighten the bolts that you remove the coating.

Just the experience I have had with powdercoating.

SD
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Old 07-07-2010, 10:09 AM   #10
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RE: "Polishing" Aluminium?

My boat is all aluminum. Part is painted white, the remainder is not painted. You could let it oxidize on its own and not worry about it; it turns a kind of gray color. I don't do anything to the boat other than wash it when it's dirty.
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Old 07-07-2010, 10:13 PM   #11
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RE: "Polishing" Aluminium?

I have powdercoated mast and boom. PC on the boom has failed at most attachment points and on the mast has held up well, both in about 10 years. Failures on the boom started in the first year and just keep getting bigger.
I have used varathane plastic paint on the pedestal under my flybridge helm seat. It has chipped off the edges of the step, but otherwise has held up better than the PC on the boom. This over about 10 to 12 years. slightly better protected environment. When I have to repair the failed PC I will use varathane or some other plastic paint.
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Old 07-07-2010, 10:20 PM   #12
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RE: "Polishing" Aluminium?

Yes but you GC have 5000 series alloy aluminum. I think all boats are made from 5K aluminum and don't corrode very much. 6063 and 6061 are very common and good also. Some alloys like 2000 series corrode quite fast.For Steve to get the best protection he should probably anodize and then powder coat. PC adheres and lasts very well if done right.The Dude speaks the truth again. But if the bolts/screws don't move one can use Sikaflex or a 3M sealer to keep them apart. For moving parts one can use bushings made of a metal that won't make a battery * * .. I don't think al and SS get along as there is significant corrosion where ever this occurs on my skiff and the manufacturer put the two metals together. Again * *..anno and PC or PC or anno.


Eric
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