Painting Aluminum

[Fotoman]

I want to repaint my aluminium boom. There is already paint on it but it's old and pealing in many places. What would be the right way to do this?

[rtbates]

yahoo search "how to paint aluminum". Read and follow directions....

[Fotoman]

Wow, search google. Great advice! Never would have thought about that one.

FYI Most hits on search engines talk about painting aluminium sidings on old houses. Hence my post. Looking for experience related to the marine use. (Why do you bother posting an answer like that anyway?)

[imagine2frolic]

Painting Aluminum - FlyingGiants Forums

priming aluminum for painting - Google Search

[Cheechako]

If there is any way to strip it clean, do so and dont paint. If painting, you need to sand completely and possibly sand blast the end fittings if you cant strip them well. Once this is done, acid wash (most paint manfacturers have this pre wash), and if at all possible prime with Zinc Chromate Primer. Then paint with compatible paint. The first coat of Primer must go on within a few hours of the acid wash (8 hours max)
Coat any stainless screws or fittings with anhydrous lanolin or Lanocote. If you must paint, could you leave the last 6 inches or so bare near the end fittings? (FYI: I had all the above done on a 71 foot mast rebuild done by a reputable firm and the bottom four feet of the mast was bubbling up after 2 years of cruising....)

[David M]

I have been painting an aluminum boat for 20 years. Ideally, you don't want to have to paint aluminum. If you can get away with bare aluminum then all the better. Aluminum in salt water hates paint! The enemy is blisters and electrolysis.

If you do have to paint then you have to knock all the loose stuff off. The aluminum oxide has to come off as well. Sanding works best...strong acids like Alumniprep, don't work so good. Forget Alodine...it still does not stop blistering. I have tried it a number of times and given up.

Forget strontium chromate as well....it does not stop blistering either nor seem to slow it down at all.

After your aluminum is bright from a very recent sanding you have to get a coat of epoxy on the bare metal. Interlux 2000 works quite well. It does not have to be the same brand as your finish coat...just get the epoxy on as soon as possible after sanding.

Forget the Lanocoat, Tef-Gel lasts far longer for bedding your fasteners or for places that have bare aluminum that cannot be painted. TefGel keeps the oxygen out which is exactly what you want to stop surrounding paint from blistering..and of course to stop the electrolysis.

Paint with whatever finish paint makes you happy.

Remember though, if you get even one ding in the paint exposing bare aluminum, you have to ASAP get it covered back up with primer to stop the paint in the surrounding area from blistering.

[Fotoman]

Thanks David. I'm starting to think I'll forget painting. How about I sand it and leave it bare? Would I still need to put something on the bare aluminium to protect it? Epoxy?

[Weyalan]

Sand to bright aluminium
Boiling water & scrub
Sand again
Epoxy primer (3 coats)
Epoxy High build primer (2 to 3 coats)
Top coat (2 coats)

[Wotname]

David M's advice is good (maybe because I agree with it ) but let me add that according to some collegues who paint Al masts (and also Al aircraft), that unlike most painting where preparation is paramount, with Al, the priming and topcoat painting conditions have to be perfect for decent job.

That precludes painting Al outside. Al should only be painted in a temperature and humidity controlled booth if you want the paint job to last.

And then you put it on the boat and ding it - protection is gone!

Bare Al does NOT need protection, the paint is ONLY for cosmetic purpose. Certainly don't epoxy it, epoxy is not UV stable.

[David M]

No, leave it bare. Aluminum oxide is actually excellent at stopping further corrosion. I know bare oxidized aluminum is ugly.

I would though bed anywhere you have stainless touching aluminum with Tefgel in order to stop electrolysis and in the case of screws, so you can if necessary, remove them in the future.

Foto...in my haste, I accidentally hit the wrong moderator button and changed your post. I changed it back to original. Thats why you see a "last edited" in your last post. My apologies.

[Robertcateran]

DOn't paint if you can avoid it. Also, avoid any carbon black impregnated materials in contact with aluminium as it can induce electrolysis. I have seen some pretty nasty stuff from a tyre used as a fender on a work boat.

[john connell]

Fotoman,

Others here will know all you need to know about painting.
If you can find the right person to do it think about soda blasting your mast.
Will do no damage to your substrate and will save you a lot of work
Then you will have a good base to either paint or not paint.
If there is any problems with doing this I'm sure someone will let you know what they may or not be but for a good quick and suitable finish hard to go past.

Regards
John

[akio.kanemoto]

Howdy,

I've spent the last few days searching and reading whatever I can find about this topic and would love to sodablast and leave my mast/boom etc unpainted - which is what several people advocate and then say "it's very common"... but I cannot for the life of me, find a single pic of an unpainted (not clear anodized either!) mast in use (i.e. not just in a yard waiting for paint...).

My mast is out of the boat, lying horizontally in my backyard and I've stripped it of fittings, and am trying to decide whether to paint or not. I love the idea of just sodablasting and leaving bare, but can't find any examples... Apparently it leaves black marks/stains on your sails etc etc...

Please, please, please help with some pics!

[Cormorant]

I read recently a story of someone who wanted to put copper antifouling on an aluminum saildrive. To get a really solid epoxy coat separating the two to prevent electrolysis, and to get the epoxy properly bonded to the aluminum, he did all the prep mentioned above -- then (because oxidation happens almost immediately after sanding/prepping aluminum) he painted on a coat of epoxy and "wet-sanded" the aluminum through the epoxy. Not a fun prospect along the length of a whole boom . . .

[brankin]

The problem with leaving a previously painted mast bare aluminum is that much of the anodized coating was etched or sanded off to get the paint to stick. If you chose to leave it bare, within a month, it will get a gray layer of oxidation on the surface and then the oxidation will stop and it will look like that forever. It is not pretty but very functional.
If you paint the mast with a polyurethane, then the mast will be prone to filiform corrosion around screw holes and anywhere you get a chip. filiform is very aggressive and will eat into the aluminum leaving deep pitting. To prevent the corrosion, you need to etch and clean the aluminum and then apply an epoxy primer that is heavy with Strontium chromate. Two types of primer
30-Y-94 Mil-Spec Primer
http://www.axonproducts.com/Technica...3%20Series.pdf

The process is remove all paint and corrosion with sander,sandblasting,soda blasting or using a laser blaster from the moon... whatever. Use an acid cleaner like alumiprep Awlgrip Alumiprep 33
to clean and get the aluminum ready for primer. Lightly spray water on the surface and note the sheeting action of the water. If the water breaks around an area, then that is contamination and needs to be re-etched. Let the mast dry overnight and then apply the primer. I put on two wet on wet coats and then a coat of sanding primer. After the sanding primer drys, then do the body work filling pits and scratches. Prime with the sanding primer again for the finish prime and then top coat.
This is what I do for a living so if you get stuck, contact me by email.

If you follow the procedures for painting aluminum, then the mast will be beautiful and corrosion free for years.