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Painting aluminum

doghead

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I don't know much about painting but, I wanted to paint a bare aluminum rowboat once and was told that you must use an etching primer. I have also primed and coated the internals of aluminum wings with some kind of etching primer / sealer. ( I don't remember what it was called but it was green in color) 2cents
 

red devils dude

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from what I know(I learned alot geting ready to piant my truck) aluminum needs a special prep coating I think it's a conversion coating of
some kind I know of one kind used in paper mill's thats a chromate conversion coating one brand is Alodine™ or Iridite® hope this helps.
 
Bjorn,
Yes, alluminum needs a special primer. Zinc chromate. Make sure all oxidation is off by using a DA or jitterbug sander or strong-armed with sandpaper. 220 grit is coarse enough.
Then "wash" the metal to clean all contaminents off ie: oil from your hands or air tools with a metal prep solution avialable at any automotive paint supply. If you want to use the cheap easy method wash with acetic acid (common white vinegar that is available.....well you know). 2 light coats of Zinc Chromate primer, let flash, scuff sand lightly and then coat with paint.
Then post pictures of your new shiny stuff. 8)
 
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primer...

The link you posted is pretty good.primer technology,and paint in general,has advanced a lot in the last few years.the metal conversion coatings and treatments mentioned are really used to deal with the thin layer of aluminum oxide that rapidly forms when aluminum is exposed to air.They "convert" the oxide to a paintable substrate.

depending on the alloy involved,the oxide layer can vary in hardness and thickness...from white powder on pure aluminum to the invisisble layer a few molecules thick on marine grades.all you likely need is an acid etch.vinigar will work (and it's real cheap)but for more severe oxidation,i had good luck with a scoth-brite pad and the stuff you find at the grocery store used to clean rust and lime deposits (CLR...LIME AWAY,etc).

these products are far more potent than vinigar,often containing muriatic and or phosphoric acids.use this liberally (wear rubber gloves and goggles please) scrub with scotch brite,and rinse liberally with water.let dry and prime asap.the oxide layer forms rapidly.

for primer,go to a commercial paint store and get a 2-part etching primer.any brand that is labeled for use on aluminum is fine.as long as it's self etching during the cure stage.
most of these primers are safe to be top coated with everything from hard enamel to 2 part urethane.check for compatibility and let your wallet choose.use a chemically "neutral" agent for sanding paper,use only stainless for a brush.no steel or iron oxide in the sanding paper.thats why i use scotch-brite.Be prepared to spend money on good primer.don't go cheap.

alodine treatment and zinc chromate were used extensively in aviation to paint aluminum,both are now harder to find and very pricey.zinc chromate especially,is being banned in canada for public use.it has long term toxic effects due to the metals it contains.getting to expensive for commercial use due to enviromental controlls required.
everybody's switching to 2 part primers,some of which are water based and much safer.

when i painted the bumper on the ford i owned,it was a heavy aluminum bull guard,etched and primed as above,top coated with the bed liner kits you buy at the hardware store.it stood up extremely well to 2 years of road-salt sand,gravel,water...you name it.no flaking or peeling.the top coat took hits from rocks and didn't even chip.
 

devilman96

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Not to be an arse to the above answers but here is the deal with aluminum... (years of aluminum experience)

Two choices... Strip... it or part and piece... The second will always cause issues with corrosion along the wear lines...

Bare aluminum should be treated with a conversion coating as mentioned... The chemicals used it this process are called Etch and Alidine last time I bought it was through a PPG store (by the gallon) but I use to use the stuff by the 55 gallon drum...

Etch does what it implies... acid washes the aluminum to open up the pores (vinegar is not a substitute for this and etch should not be applied over paint)... Alidine is the "conversion" which flashes the metal and gives it a goldish yellow look... If you skip this process paint (even high dollar chromates) will not adhere well and / or will corrode... If your going to do this with the cab in place on the truck keep in mind that the Alidine will change anything it touches.

There are a billion options for primer but it more depends the area being sprayed... if it is a panel (not walked on) any zinc chromate will do... if it is a traffic area you need to use a chromate epoxy (primer that takes a hardener)...

If you have corrosion it is important to get it cleaned off before you do anything... There is a special type of grinding disc make for doing aluminum referred to as "nylex"... They come in a silver or orange color and look like a wire wheel but made of little plastic looking fingers, they are made to be used at low RPM as the wheel will burn if to hot... . You don't want to use, steel, iron, stainless, brass or sand as it impregnates the aluminum and will cause it to corrode even worse, aluminum oxide sand paper and aluminum oxide blasting media only...
 

rdixiemiller

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Find somebody who paints aircraft in your area. They will be able to help you with the proper chemicals and primers. That is usually the best thing to do. Getting paint to stay on aluminum can be trying at times!
 

cranetruck

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Thanks for all the information!
Fortunately, only a few spots are bare aluminum, so most new paint will go over lightly sanded old.
You know me, love to post pictures so you'll get them, count on that. :)

Edit: Noticed that the words "US ARMY" have been removed across the top in the picture....
 

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CGarbee

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This thread has been (and is) very helpful and informative to me as I will soon be putting paint on my '68 M274A5 Mule. The A5 Mules have aluminum decks, and mine is pretty bare right now...
I'll be posting photos and sharing info as I go along, and am looking forward to comparing finished products this spring... :)
 

CGarbee

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cranetruck said:
The PS magazine refers to the Mules as having a magnesium deck, must be an alloy, huh?
You are alert Bjorn!

The M274A5 is the only Mule in the series to have an aluminum deck instead of magnesium. It is also the only one to ship from the factory with two wheel steer (although you can convert it to four wheel steer using parts from any of the earlier models, and I plan to on mine).

Olive Drab has a good page that runs down the differences in the series located at:
http://www.olive-drab.com/idphoto/id_photos_m274.php3
 

CGarbee

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Frank,
Please put it in the collection of stuff that you are putting together for me. I'll make a run down your way sometime this month (have to check the work schedule)...
What I don't use on my project, I'll pass on to Bjorn...
Thanks,
 

cranetruck

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Again, thank you all for the advise! The priming part of the paint job is not going to be very extensive, only several small spots have worn through to bare aluminum, one notable is the driver's floor boards and places where I sanded through the layers to find markings.
Cabell probably has a much more extensive job with his Mule deck.
 

FrankUSMC

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Bjorn
If you have just some small places to paint. I will give Garbee some spray cans of Zinc Chromate to pass on to you. He can have the two gallons to do his mule with.
One of the few, Frank
 
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