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Old 01-06-2008, 17:18   #1
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paint stripper on aluminium mast?

So, having pulled 60' of aluminium out of 40' of fibreglass...

The paintwork on the mast is very tired and in places non-existent. So we plan to repaint.

Is there any reason why we cannot use paint stripper on the alloy mast?

If we can use paint stripper, is there a particular type that will be best in this application? I'm guessing that the paint would be etch-primer, primer then 2-part enamel or similar... like I say, in varying degrees of direpair.

Thanks
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Old 01-06-2008, 18:55   #2
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It seems unlikely that stripper will affect aluminum but check with the manufacturer of the stripper. There is probably a number to call on the can.

A bigger issue is getting a substrate that will adhere to the new paint. Anodize and Alodine are the two most frequently used surface preparations for aluminum. Anodize is electrostatic ally applies and usually requires immersion of the aluminum. Not easy to do with a mast. Alodine can be brushed on.

There will be finishing shops than can advise you. I find that most are willing to share knowledge, even if you plan to do some or all of the work yourself.

George
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Old 02-06-2008, 00:41   #3
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Avoid caustic paint strippers.
It is possible the mast was powder coated, which I don't believe paint stripper will touch. You will soon know, it'll either work or not.
Once you have stripped, you need to thoroughly clean away any corrosion and wash the ally with a pre-paint wash/degreaser. Then you etch prime, followed by a paint system. I suggest a two pot because it is hard wearing. I have not used, but have heard about a product called Nyallic (spell?).

Anodizing is specialised. It requires the mast to be dropped in a tank of acid and an electric current passed through with the tank being the cathode and the alloy being the Anode, Hence anodizing. The ally corrodes and builds up an oxide layer, with the thickness determined by current and time applied. After the thickness of the layer has been achieved, the ally is then dyed with a colour. The oxide layer is a series of open pores. Once the colour is taken in, the ally is dipped in boiling water. Boiling closes the pores and the colour is locked in. The resulting coating is hard wearing and protects the metal below from corrosion. I anodize all my own small ally parts I make. It's a lot of fun, except I don't do the dyeing as the chemicals are usually heavy metals and very toxic.
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Old 02-06-2008, 03:23   #4
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Quote:
Originally Posted by Alan Wheeler
... I have not used, but have heard about a product called Nyallic ...
NYALIC < Nyalic - polymer resin coating that provides surface protection for years. Ultraviolet protection | corrosion protection | clear surface protect | protective coating >
is a nylonic (industrial secret), crystal clear polymeric resin coating that provides years of protection against chemical, environmental and ultraviolet corrosion on ferrous and non-ferrous metals (Aluminum), galvanized, anodized, powder coated and painted surfaces. It also works well on plastics, fiberglass, concrete, stone and masonry and even on wood.
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Old 02-06-2008, 23:20   #5
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I work on aircraft that spend their time in a marine environment. The strip and paint system we use is an aircraft stripper by the brand name of Mar-Dan It is a polyethylene-chloride stripper. It smells like latex, but it certainly does not feel like latex when it comes in contact with your skin. Just remember to keep plenty of water around for rinsing if you do get it on you! Then we mechanically clean the surface with teflon wheels on a small drill motor or die grinder. The soft teflon (white) cleans the metal without scratching it as long as you do not use too much pressure. We then etch the surface with alumi-prep, followed by a rinse and dry, then we alodine the surface, usually with a foam rubber brush. We then use the self-etching epoxy primer. This is finished off with a two-part plyurethane finish coat. We usually use a single-stage ployurethane for ease of use and weight savings. In a marine, working environment, these planes usually last a couple od decades between paint if kept clean. We usually use DuPont IMRON unless otherwise specified by the customer. IMRON is used by fire truck manufacturers as it is a very tough paint.
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Old 03-06-2008, 02:10   #6
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HAWK180:
WOW - Thanks for the excellent information.
BTW: Welcome aboard the CF.
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Old 03-06-2008, 03:19   #7
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Check this link out..... Scroll down the page a bit.

The Complete Refit of Trim -Part VI | S/V Trim

I need to refinish my mast in the next couple of years, this is the way i've seen the local "experts" do it with excellent results with rigs like yours.

Don't know about applying heat to remove corroded in fastners though - you would have to be really careful not to affect the temper of the alloy. Is the way to do it?

I need to remove an unused exit box and the PO did not an anti-corrosive compound (eg duralac) and the machine screws will not budge - I'm afraid I'll shear the head off if I apply too much pressure.
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Old 03-06-2008, 08:01   #8
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I run an aluminum boat for a living. I use plain old Jasco paint remover and it does not harm the aluminum at all. Paint remover will not remove anodizing since anodized aluminum is a very hard aluminum itself. What you never want to put on aluminum is sodium hydroxide or what is commonly known as drain cleaner. Sodium Hydroxide (NaOH) dissolves aluminum.

What you do use to prepare aluminum for painting is Alumniprep 33 for removing oxidation in hard to get at places and Alodine 1201 which is a chemical converter and helps the primer paint adhere to the aluminum.

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Originally Posted by Spirit28 View Post

Don't know about applying heat to remove corroded in fastners though - you would have to be really careful not to affect the temper of the alloy. Is the way to do it?

I need to remove an unused exit box and the PO did not an anti-corrosive compound (eg duralac) and the machine screws will not budge - I'm afraid I'll shear the head off if I apply too much pressure.
Try putting a few drops of Alumniprep 33 in the area where the stainless screws into the aluminum. Apply the alumniprep, tap the fastener, let it sit, tap it some more, rinse with fresh water, blow it out with an air hose...repeat the process for a few days or until it comes out. The Alumniprep dissolves aluminum oxide.

As far as heating goes, aluminum has a much greater expansion rate than stainless, so you don't have to heat aluminum up all that much to make a difference. You wont change the temper of the aluminum as long as you keep the heat down and stay well below its melting point. In my experience, sometimes these two tricks work and sometimes they don't.

Why some people screw stainless into aluminum without applying something to displace the oxygen is beyond me.

When screwing the stainless back in, use Tef-Gel to prevent oxidation from seizing the screw in place again. In my opinion Tef-Gel is the best stuff for this application because it remains gooey and never hardens...therefore displacing any water or oxygen that would otherwise get in there. As aluminum expands an contracts, the Tef-Gel stays there, unlike some bedding compounds which can delaminate or shrink, eventually allowing water to get in.
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Old 03-06-2008, 08:26   #9
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I don't think that anodizing would be a very practical solution. We use a few shops for our anodizing but the abosolute max length that they can dip is 20'. I would imagine that there must be a way to anodize 60' of alum but I think that cost would quickley outweigh the time that HAWK180's method would require. However, I would say that we don't recommend painting our Almag castings because anodizing has a much higher tolerance for marine stresses. As Alan said, anodizing essentially "pre-oxidizes" the alum, preventing any further oxidizing.
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Old 03-06-2008, 08:36   #10
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Hobies have anodized masts that are well over 20 feet long so I would imagine there is a way. I have seen anodized masts oxidize where stainless fasteners are connected. So although anodizing is good, there is no perfect solution for stopping aluminum from oxidizing.

Also, powder coating aluminum is pretty much worthless. I bought a powder coated aluminum conducting cable winch and it was blistering in less than a year. Anywhere bare aluminum is exposed to the atmosphere, it will blister the adjacent paint or remove the anodizing regardless of how tough the paint is or how tough anodizing is.

I think that anodizing comes closest to a perfect solution....which of course does not exist.
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Old 03-06-2008, 08:50   #11
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Powder coating is tough but IIRC it is not impervious to moisture which is why it doesn't last long in the marine enviroment. Two pack paint is more imprevious to moisture than powder coating (but not as tough).
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Old 03-06-2008, 08:57   #12
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Good point David. Powder coating is just asking for trouble. We get all kinds of calls from people who powder coated their davits and ask about re-anodizing (which also isn't always a good idea).
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