Painting smooth aluminum parts?

Discussion in 'The Garage' started by mslim, Jun 3, 2019.

  1. mslim

    mslim If it's worth doing... it's worth overdoing

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    I'm curious about refreshing the stock Magura control perches and levers on my Airhead. I have a damaged one to experiment on. I was curious if they were anodized, but light sanding revealed it was clearly paint. I plan on sanding the old paint off and finishing with 400 or 600 grit to give a little tooth to adhere the paint. I didn't see any evidence of a primer coat when I sanded the test piece down but who knows? This is going to be a rattle can job so 2 part epoxy systems are off the table.

    I thought that some of you aviation types might offer some guidance on making paint stick to aluminum. I see references to etching primers (specifically SEMS) on the internet. I know a lot of aviation parts have zinc chromate on them.
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  2. Flipflop

    Flipflop Long timer

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    These days the Awlgrip G line uses Awl-wash as the primer, which isn't chromate based. They only sell quarts of A and B, at the small size so not much good for small stuff. If you've got any plane or boat painters around that could be hassled for an ounce or two that would be one way to go. Awlgrips 545 primer is world class.

    Alodine would be another wash you could use, but again the small portion size isn't the specialty. Read the MSDS on that before you get too involved...

    You can use Dot3 brake fluid to strip the old paint, or EZ off oven cleaner... Saves a bit of time on housings.

    The SEM brand spray paint is good stuff. 400 is as fine as you want to go for the initial coat, much finer than that and you lose the mechanical tooth for the paint to hang. Go over it with fresh sharp paper once your happy. I'd investigate SEM Gloss Trim Black.

    I'd use maroon scotchbrite after sanding to get into the details that paper doesn't like to conform to and shoot it and work up to a decent thickness of paint in thin shots. The inside of the housings can be a pain in the ass so you may want a piece of cardboard to block half the fan to get the inside corners so you don't puddle. Spray cans work best vertically, so hanging so the housing faces you works best. Change bolt holes for hanging so that you don't miss painting the inside of one screw hole or the oxidation will flower out of it.

    Scuff with scotchbrite in between coats. You only get 10 minutes or so before aluminum oxide starts forming again on aluminum, so scuff it, acetone or denatured alcohol wipe it and then shoot the first shot.

    Only handle the parts with nitrile gloves on once you acetone wash as the oils off your skin leaves marks you can see in the paint.
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  3. usgser

    usgser Long timer

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    In the marine industry we've had a lot of cargo/passenger gates, ramps made along with alum cargo dividers, hold downs etc All exposed to weather/sea conditions and we always used a zinc chromate primer on alum. W/o it paint doesn't stick well at all.
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  4. Renegade6

    Renegade6 Been here awhile

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    What about using self etching primer and then a top coat? Be careful what product you use to strip aluminum as a lot of the caustic products will discolor it.
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  5. Beezer

    Beezer Long timer Supporter

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    as above, caustic on aluminum is not so good, and red scotchbrite is what I use for tooth. for simplicity and low budget.... self etching primer is the way to go. go to an auto paint store that sells the big names like DuPont and PPG, they will have something rattle can that will be a cut above grocery store materials.

    to strip paint, pour stripper into a baggie, drop in the part, zip it shut, and let it sit. you can work the stripper through the bag occasionally until its done. for bigger parts I use 4 mil sheet plastic to cover the goo
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  6. Beezer

    Beezer Long timer Supporter

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    and you still need prep if you use zinc chromate unless it is self etching. it's great stuff. I like Stitts, but thats 2 part (3 actually). to test your prep on bare metal, do the "water break" test. might be hard to see on a part with multiple angles & such, but on flat sheet it's pretty easy. you clean and scuff until you think its ready, then flood with water. if it's OK the water will form an even, continuous sheet. if there is anything still on the surface, the water will either bead up or there will be a void in the sheet. if the surface has been wet in the last couple days, blow out seams, rivets, and boltholes with clean compressed air. if you use a wax and grease remover prior to paint, blow everything again because that stuff gets deep into cracks and will make the paint creep (thin out and/or pull away).
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  7. kantuckid

    kantuckid Long timer

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    Walmart etch primer is good stuff-Dupli-color brand name. It also works with mixed AB paints too and prep & clean is a constant for any primer or paint. I would not use a rattle can top coat on a lever as it will suffer from UV fast.
    I use it all the time and as a former helo mechanic it works just fine for small jobs.
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