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Randy Jones

unpainted aluminum masts

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I'm switching from wooden to aluminum mast for my CS17.  The mast kit from B&B is going together nicely and I've started to think about paint.  Other than appearance I can't see any reason the masts need to be painted.  How does an unpainted aluminum mast look in a few years?  Has anyone tried a brushed finish and left it to oxidize?  Am I overlooking something?

FYI, I love the original wooden masts but they are tapered too thinly to accept sail track and the lacing is inconvenient. 

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The raw 6061 alloy will oxidize pretty quickly and develop the gray coating we're all accustomed to seeing. This sloughs off easily making everything it touches black. If you want clear, I'd go with an LPU or even an automotive acrylic urethane. If paint, the same options apply for best durability, though you may want to consider having them powder coated (clear or color). I don't have an oven long enough for the spar pieces, but I'll be you find find a shop with this ability, even if it's just UV heaters. I'd try fence and railing manufactures for this. Other paints are options, though not nearly as durable.

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Consider using this stuff too for a clear finish.

http://www.nyalic.com

Rattle can application is easy.

I did the aluminium on my current boat in 2007 and it still looks good as new.

The only thing it doesnt like is any sunscreen spilled/ left on it.

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That stuff is a single part polyurethane and not as durable as the 2 parts versions, though better than most single part paints.

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Do you have the epoxy-based single coat enamels in the US? I would imagine you would and I wonder how it would hold up on aluminum, since it is promoted as an anti-corrosive and claims a long life. This is one example http://www.whiteknightpaints.com.au/specialty-paints/metal/rust-guard/topcoat/epoxy-enamel . I'm sure PAR can shed some light for us. I am soon to paint my mast too.

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I can't find any info on what exactly that White Knight paint is.  Epoxy is a 2 part reacting material.  Petite Easypoxy is a polyurethane,  it has no epoxy in it.  I think they find marketing value in using epoxy in the name.  When I look up epoxy enamel all I find is 2 part paints.

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Anytime the word epoxy can be used in a product name, you'll sell more. Most of the "epoxy" single parts use elements of the bisphenol A molecule in the formulation, so they can say "epoxy" on the label. The term enamel shouldn't be used with epoxy, as their chemistries aren't compatible, but (again) it's a sales technique. The two part enamels are likely epoxies, but using the enamel product description to improve sales.

 

The  "White Knight" stuff looks to be a rebadged, PPG product. 

 

I've I were painting an aluminum mast, I'd use a good epoxy (2 part) primer, then over coat with a LPU (first choice) or a hard single part acrylic urethane (second choice) or polyurethane (single part, third choice). 

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Thanks everyone.

I was just trying to be lazy and avoid painting altogether.  My leftover System3 Silver Tip Yacht Primer (two part epoxy) and System3 LPU sound like ideal choices.  

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We painted ours with a good quality rattle can paint, seems like the act ( or art ) of trailering caused little scratches.  So every now and again I just touch up the scratches with the spray can.  I coated the inside of the mast with ACF 50,  which is a anti corrosive compound initially used in aviation industry.  I sucked a light line through the masts with a vacuum cleaner then tied a big fluffy old hand towel soaked in ACF 50.  Then hauled the rag back through the mast.  3 years no corrosion on the mast yet!  

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I tried the leftover bits of S3 Waterbased LPU.  It comes off quite easily from getting chewed up around the mast steps.  It is easy to touch up, but will go with an epoxy base next time prior to painting.  No corrosion that I know about so far.  

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On 12/5/2017 at 2:55 AM, Randy Jones said:

...I was just trying to be lazy and avoid painting altogether...

   I didn't put any finish on Southbound's masts.  My thinking (which could well be incorrect) was that the process of tempering the material to T6 had already artificially aged (anodized) the surface.  Since it's been a few years since I've seen the boat I can't speak for how well the masts have stood the test of time or whether the sleeve-luff sails ended up black but Alan certainly can.  Hopefully he will share his observations here.

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Aging of aluminum is different from anodizing, which is a specific electrochemical process.  

 

The thing with the aluminum is to get a good substrate prep.  Use one of the aluminum etchants (some are pretty nasty so ventilation and adherence to instructions is the thing) and aluminum specific primer application right afterward.  Then the finish coat.

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   Yes, they are different processes and it was my understanding (possibly incorrect) that both of the processes resulted in an oxidized surface.  I didn't express my thinking well in my previous post - I typed "anodized" where I meant to typed "oxidized".  I'm still not sure I'm correct, though. :)

   Southbound has sleeve-luff sails and during the five-ish years I sailed her the sails were stored rolled up on the masts so the sails were constantly in contact with the uncoated masts.  I don't remember the sails turning grey but is has been a number of years since I moved to Australia and I may just be a victim of selective memory here.

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Aluminum, just like everything else needs to have some "tooth", cut into it for a good coating bond. This means sanding or a chemical etch. As soon as the sand paper moves from the area you just sanded, the aluminum starts to oxidize (literally within seconds), so you have to work fast, if mechanically keying (sanding) the surface. If you're going to epoxy coat the surface, West System recommends you employ wet/dry paper or a scouring pad, in the wet goo, as you apply the epoxy, creating a scratch under the epoxy as you applying it. This protects the aluminum from oxidation, as it's under the wet goo during the process. I've done this and it's a messy way to go, but the results can be really good.

 

For most backyard builders a chemical etch is an easy method, either with a etch primer or a two step system. I use to do it this way, but now having a real spray booth, I do it differently, literally sanding and squirting primer at the same time. This is at best a two person job, with one wet sanding the aluminum, but without water (I use a alcohol, thinner mixture, based on the paint I'll spray). As the sanding is being done, any mess is caught and sucked out of the booth with a special made 20" ducted fan. The aluminum is dried, sometimes forced (heat gun on low) and the paint is sprayed directly onto the surface, a few feet from where the last rub down occurred. I find this faster and less messy, but this technique is reserved for things I know need to be very well bonded, like LPU paint jobs. For the home builder, the more common paint brands have good etch primers and this is my recommendation. Sand as necessary, if only to remove the most recent oxidation, then get it clean and dry, so you can apply the paint, as soon as practical. This is the ticket for aluminum painting, the amount of time it remains uncoated after a fresh sanding. If you can get paint on the part within a few minutes, your bond will be excellent, unless you're painting in the rain or a high humidity day, at which point you should have known better, as painting in the rain makes for a bad hair day, at the very least.

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I used the Rustoleum Marine finishes for mine.  I sanded immediately before applying the etching primer.  I tipped and rolled that and the fi al coat of white.  It has held up very well, except for the sections of high compression (where it bears against the deck and seat t the top of the mast tube).  I would use this product again, but consider a clear coating )or no coating)  for the lower bits.

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