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How To Prep Aluminum For Paint

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  • How To Prep Aluminum For Paint

    I am making a power control box and want to paint it. It is going to be housed in a new aluminum chassis box. I have cut and drilled all the holes, removed the protective plastic film, and it is ready for paint. I plan to use Rustoleum Metallic Gray Hammertone. I have had problems with paint sticking well to these aluminum chassis boxes in the past.

    What is the best way to prepare the surface prior to painting. The can says that primer is not necessary. But is it? Or what? Rough up the surface with sandpaper? Steel wool? What?
    Paul A.
    SE Texas

    And if you look REAL close at an analog signal,
    You will find that it has discrete steps.

  • #2

    The traditional way of preparing aluminium for further paint coats is to use zinc chromate primer - the yellowy-green stuff. Common on aircraft, and it would probably do the best of all jobs.

    But as this is a power supply, that presumably won't be living its life in constant seawater spray or the like. I'd just scuff the surface with fine emery paper, wipe it with paint thinners and spray the topcoat straight on - maybe a couple of coats. Round off any sharp edges first.

    All of the gear, no idea...


    • #3
      As Ian B noted Zinc Chromate was the protocol primer for Al. Haven't used it since I got out of the Coast Guard in 72. In those days it was referred to as Green Death!
      John B


      • #4
        isn't there some treatment before the zinc Chromate?

        The problem with AL is of course that the surface very quickly to get a durable finish on something facing a tough environment is challenged without all specialized chemicals.

        otoh, for light duty stuff, like models, I've just gone ahead and painted it and its lasted beautifully. The photo almost looks to have a coating its so shiny? I would scuff it up and paint.
        in Toronto Ontario - where are you?


        • #5
          I used etch primer from the paint dealer, does the job, probably some acid or some such in it


          • #6
            As said before Scuff it up good , wash with soap and water and scuff again. Then use self etching primer.


            • #7
              When we painted the mast for my friends sailboat 15 years ago we used something called a "self etching primer" prior to painting. It's held up
              pretty well:

              Whenever you wipe down with solvent make sure you wait long enough for all the solvent to evaporate prior to any spraying or you'll get
              fish eyes in your finish.
              Location: Long Island, N.Y.


              • #8
                etching primer followed by a high solids epoxy based paint


                • #9
                  That box is a neat job.
                  If I could do that I would leave it natural.

                  With the bike parts I machine from 6061, some are 2 years old, have been out in winter slush etc,
                  and they are still nice and shiny


                  • #10
                    Bonderite from Aircraft Spruce



                    • #11
                      Why do you want to paint it? It looks great just the way it is.

                      When I had to do this from time to time at work before I retired I used to bead blast and then prime and paint with Krylon spray.


                      • #12
                        For etching the surface dump the entire thing in lye for a few minutes. Wash off well.

                        Lately I've been giving aluminium a light bead blast prior to painting. Then a quality primer and top coat. I use the Rustoleum industrial primer followed by (5 minutes later) 2 top coats of Seymour engine paint for a very fast drying high gloss.
                        Last edited by lakeside53; 07-16-2017, 11:42 AM.


                        • #13
                          The best surface prep. is abrasive blasting with fresh Alox grit to give the surface some mechanical tooth. Then follow with an epoxy paint like Brownells Alma-Hyde II. It is mechanically tough as well as very solvent resistant. A 2-pack urethane or epoxy paint will be better, but impractical for a small project.



                          • #14
                            On boats we use ALUMA BRITE it is a 10% hydrofluoric acid and 10% phosphoric acid solution. Mix 50/50 with water, spray on with a garden sprayer, let sit then, hose off with water. The AL looks like it was sandblasted. Blow dry and then paint.


                            • #15
                              Originally posted by Mcgyver View Post
                              isn't there some treatment before the zinc Chromate?
                              You are probably thinking of Alodine. My local automotive paint store stocks it at a reasonable price and a bottle lasts a very long time.

                              Scotchbrite/sand/bead blast the item, clean it thoroughly right away, then wipe on the alodine. If it really needs to last, follow with zinc chromate primer or one of the newer substitutes.
                              Location: North Central Texas