coating aluminum spars? - Page 2 - SailNet Community

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Go Back   SailNet Community > On Board > Gear & Maintenance
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  #11  
Old 03-06-2010
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Quote:
Originally Posted by davidpm View Post
Is this true?
You could get the spar anodized instead of powder coating it. While aluminum will oxidize and form a protective coating, it is not a very hard coating and not very protective, especially in a salt water environment. I would highly recommend painting it with a good two-part LPU paint.
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  #12  
Old 03-06-2010
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Let's see. I guess I haven't posted on this particular painting aluminum thread yet so here goes. For a number of years, I refinished aircraft and was damned good at it. My procedure for aluminum went like this.

1. Chemically strip all old paint with an acid (formic) or phenolic stripper.
2. Once all traces of paint are gone, brass brush (with a drill) any corrosion away.
3. Acid etch (and scrub with a red scotchbrite) the bare aluminum and flush thoroughly with water.
4. Alodine the bare aluminum and rinse with water after 5 minutes or it turns a nice golden color. Make sure ya spray it evenly as any streaks will cause the primer to fail.
5. Apply a Zinc Chromate or epoxy primer.
6. Apply Alumagrip, Imron or similar Polyester Urethane paint.

This coating should last a minimum of 10 years.
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  #13  
Old 03-06-2010
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Zinc Chromate primer is an important step.
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Old 03-07-2010
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I did my mast and boom with perfection. I followed the steps that interlux suggested, and it turned out great.

1. Remove all hardware.
2. Sandblast.
3. Apply primer for aluminum within 2 hours of blasting.
3. Prime with Epoxy Primer for Perfection.
4. Apply Perfection.

I used flattening agent with my perfection because I didn't want a shiny mast. I also sprayed all of the coats of paint. It came out great, has been very tough, and after a full 3 years there has been no problems.
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Old 03-07-2010
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Quote:
You could get the spar anodized instead of powder coating it. While aluminum will oxidize and form a protective coating, it is not a very hard coating and not very protective, especially in a salt water environment. I would highly recommend painting it with a good two-part LPU paint.
SD,
Can't say long term, as mine were done just two years ago. So far, so good. Many aluminum boats in Europe are left bare and fare well, which was the source of my thoughts on leaving the mast and boom paintless. I did a quick survey of aluminum structural material around the port, and became convinced that the oxide will protect long term. Of course, there are many diferent alloys, etc... I'll post pix in about 10 more years! The one advantage that put bare over the top for me is the ability to inspect fittings, structural joints, etc, for any signs of stress failure before the crash.
Again, to each his own. There are valid points both ways.
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Old 03-07-2010
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I didn't mention that the PO had the boom extended about 15 inches by inserting a sleeve, then adding a matching section so he could to move the mainsheet & traveler aft when the steering was converted from tiller to a wheel. The extension was welded, and the sleeve riveted. I was told this done by a very well known and reputable yard, but the appearance of the rivets makes the option of bare aluminum (or clear anodizing) undesirable to me from a cosmetic point of view. The splice is at the end of the boom that attaches to the mast. I visited a powder coating shop with the spar yesterday. They do a lot of marine work, but I think it's mostly towers and other hardware. I don't know how many spars they actually do. Their quote was $480 for sandblasting, phosphate wash, primer and 2 finish coats of white powder. (That was before the concern about the powder coat cure temp on the aluminum temper was raised. I didn't ask about what temp their curing oven uses.) I'm reluctant to spend that much because I suspect that the powder coat will eventually fail around rivet heads and require re-coating. I think I could buy a sandblaster for that price.... I don't know if I want to learn how to sandblast on this spar though... The powder coater told me that it takes some skill to get an even finish when sandblasting a failed coating due to un-even material removal rates.

Is there a chemical stripper that will remove algrip from aluminum?
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Last edited by ChuckA; 03-07-2010 at 12:33 PM. Reason: fix spelling
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Old 03-20-2010
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I bought an variable speed random orbital sander and started stripping the paint today. It came off reasonably quickly with a medium grit. The higher speed setting (12,000 rpm) seems much more effective at paint removal than the lower speed (7000 rpm). It took me 3 trips to the store to get the adapter to hook it to my shop vac, and get disks with the right vent pattern for the vacuum. The 120 grit seems fine enough to give a reasonable cosmetic surface. It is looking so nice, I'm starting to consider leaving it unpainted. I'm curious though. If I leave it bare, should I apply something like wax or teflon polish to slow down oxidation? I don't want my sails to get stained by the boom. There are some places on the boom, where even after sanding off all the finish, there are still some cosmetic imperfections in the surface. where corrosion has penetrated into the surface so a bit more metal removal would be needed to remove it all.

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  #18  
Old 03-21-2010
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In a prior discussion on mast finishes someone suggested putting some type of oil finish on bare aluminum. I don't remember the details but you could search for it.
I painted my mast 2 years ago with Alwgrip and it went on nicely and looks great. I just brushed it but am happy with the result. Getting the mast stripped is the hard part.
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Old 03-22-2010
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Here is a shot of my mast at about 3 years and now at 5 years it is looking a little faded and has some places where the paint is wearing thin and a few chips from contacting things while steping(about a hundred plus times).

It was anodized and looking bad when I started.

After removing all hardware I stuffed 10 ft. fence posts in each end so I could suspended it between saw horses with out it bowing to bad.

I used a high speed air die grinder and 2 inch brown 3M sanding pad to remove any white spots and to give the paint a good hold.

I wiped it down with laqure thinner to remove any oil.

The next morning I wet down the area with the hose ( I'm working in dirt but it is an old trick to keep the dust down when ever you want a dust free paint job), one more wipe with thinner and wipe down with a tack cloth and I was ready to paint.

I use Rustolem(?) white and put it on with a foam banana roller starting at the top and working all the way around and down.

I didn't try to get paint into the track because I thought that might be a place for to much wear, just rolled lighty there painting just the top.

I waited untill the bottom was tack free and then tacked it off and put the second coat on.

Time for the job, not counting the disasembly and reasembly, four hours.

Cost for job, about $25.

It does take about a week for this paint to dry (No paint smell no matter how close you put your nose) because it is oil based.

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Old 03-22-2010
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Here is a shot of the finish smothness today.

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