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Thread: Clear Coating Aluminum

  1. #1
    Join Date
    Mar 2005
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    Pittsburgh
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    425

    Clear Coating Aluminum

    I have a question about applying finish to aluminum. I am building a large table with a modern flair and it requires I use aluminum inlaid in the maple, actually the aluminum is the structual part of the table halves. I have concerns with the finish holding up (bonding). Most likely I'll be using some sort of catalized lacquer, pre or post catalized. I remember years ago about applying paint to metals like aluminum or stainless steel and you would have to coat them with vinegar or some type of an acid to give it tooth. I'm not sure what is required of the new lacquers. My thoughts are I see guys with aluminum wheels on their vehicles and the wheels are all clear coated. Granted the clear coat was applied and then baked on, I understand that. I know ask the wholesaler but sometimes they know less than the guy on the street. I thought someone here may have come across my situation before.

    thank you
    Ben

  2. #2
    I have tried spray lacquer on aluminum with mixed success. Sometimes it seems to stick fine and other times it peels very easy. All the times I have coated the aluminum it has been sanded to a brushed finish look first. At my previous employment aluminum would get acid etched before priming and painting

  3. #3
    The aluminum wheels on my 14 year old Tahoe didn't hold up very well.

    For exterior use, you really need to use specialty coatings in order to get it to hold up reasonably well. Aluminum is subject to unique forms of corrosion when coated and even in the marine industry its hard to prevent capillary effect corrosion. Whole books have been written on this subject alone.

    For interior use, I wouldn't worry about it as keeping a finish on shouldn't be a problem. IF you have aluminum in contact with frequently wet wood, you will have corrosion problems (as in spilled drinks that migrate down into the substrate.)

  4. #4
    Join Date
    Sep 2013
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    Connecticut
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    If you can get the aluminum clear anodized you can have an incredibly durable coating that doesn't need a finish.

  5. #5
    Clear coating aluminum with satisfactory results is actually quite difficult. Definitely etching, with something like Metal Prep 79, will almost certainly be required, but you always get the best results by scrubing with something like scotchbrite, and etching, followed by some sort of primer, and then paint on top of that. Also, there are many different grades and formulations for aluminum, and not all are treated the same way.

    I would lean towards anodizing, or maybe even bright dip anodizing, if you have an alloy that will support it.

  6. #6
    Quote Originally Posted by John Coloccia View Post
    Clear coating aluminum with satisfactory results is actually quite difficult. Definitely etching, with something like Metal Prep 79, will almost certainly be required, but you always get the best results by scrubing with something like scotchbrite, and etching, followed by some sort of primer, and then paint on top of that. Also, there are many different grades and formulations for aluminum, and not all are treated the same way.

    I would lean towards anodizing, or maybe even bright dip anodizing, if you have an alloy that will support it.
    Yeah, and after you abrade the clock starts ticking because the aluminum is oxidizing quite quickly and it is that process that interferes with proper adhesion.

    I had some funky aluminum parts I needed to paint a few years ago. They were quite small. By the time I got them cleaned-up, I had maybe a few minutes to get the bonder onto the aluminum so it would stick.

    A month later I had another batch and they used some other type of aluminum and those went quite well (the aluminum didn't oxidize anywhere near as quickly).

  7. #7
    Your best bet is a phosphoric acid etch (like PPG DX533) followed by a 2k urethane isolante coat, I like Chemcraft but have had good results with Ilva as well. After the 2k isolante has dried for an hour you can spray your sealer coats on and should have no problems. Whatever you decide to do make sure to do some adhesion tests on some scrap aluminum first as you do NOT want to have to fix the finish peeling off the inlay on a table top.
    Last edited by Keith Outten; 11-23-2014 at 6:30 AM.

  8. #8
    The isolante hardener contains isocyanates, nasty to begin with but even more nasty because dangerous exposures occur at levels low enough that you can't even really smell anything. Just FYI.

  9. #9
    Join Date
    Nov 2006
    Location
    NE Ohio
    Posts
    6,983
    Give these people a call. XIM Technical Support Desk at 1.800.262.8469 x120

    They can walk you through the selection of proper primer to use and proper surface prep.

    I sold the devil out of their products 35/40 years ago and never had any complaints from anyone.
    Last edited by Rich Engelhardt; 11-22-2014 at 7:22 AM.
    My granddad always said, :As one door closes, another opens".
    Wonderful man, terrible cabinet maker...

  10. #10
    As mentioned above, aluminum clear anodized would be my choice.

  11. Some of the other post made me think, why not powder coating the aluminum? I know the stuff is incredibly durable and I think it can be done in clear. You would have to consider the thickness of the powder coating though

  12. #12
    Quote Originally Posted by Mark Woodmark View Post
    Some of the other post made me think, why not powder coating the aluminum? I know the stuff is incredibly durable and I think it can be done in clear. You would have to consider the thickness of the powder coating though
    My experience with powder coating is if you have any sharp edges or details, the coating will either not adhere well, or it will bunch up in the corner. The thickness will also vary wildly with the skill and care of the shop doing the work. I see a lot of powder coat that is excessively thick and even sometimes just peels off. I think it's a great finish, but for something like this where the aluminum will be structural and aesthetic, and it all needs to fit well, I think anodizing is a superior process.

  13. #13
    Quote Originally Posted by Rich Engelhardt View Post
    Give these people a call. XIM Technical Support Desk at 1.800.262.8469 x120

    They can walk you through the selection of proper primer to use and proper surface prep.

    I sold the devil out of their products 35/40 years ago and never had any complaints from anyone.
    XIM is the bonder I've used on aluminum and it holds well provided the aluminum is properly prepared.

  14. #14
    Join Date
    Nov 2006
    Location
    NE Ohio
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    6,983
    Exactly - surface prep (as mentioned above a few times) is critical.
    The surface prep process is a bit too involved to go over here which is why I said it's best to call XIM.
    My granddad always said, :As one door closes, another opens".
    Wonderful man, terrible cabinet maker...

  15. #15
    Quote Originally Posted by John Coloccia View Post
    My experience with powder coating is if you have any sharp edges or details, the coating will either not adhere well, or it will bunch up in the corner. The thickness will also vary wildly with the skill and care of the shop doing the work. I see a lot of powder coat that is excessively thick and even sometimes just peels off. I think it's a great finish, but for something like this where the aluminum will be structural and aesthetic, and it all needs to fit well, I think anodizing is a superior process.
    Too bad, I was considering it for a project I am currently working on. I have had some 6061 aluminum extrusion color anodized before and was not impressed with its durability. It was not as good as I have heard. I have wondered if it was the shop I used. I worked for a manufacturer that color powder coated some of their parts. I cant remember if I noticed that they broke the edges of those parts prior to powder coating. They did have a learning curve in regards to the thickness thing though. My question is now; What do the automakers use on their aluminum wheels? I have noticed that some OEM aluminum wheels have a clear finish applied to them. I would think that a car wheels paint would need to extremely durable.....I am curious about all this as I have been trying different metals for inlaying and more

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