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How To Prep Aluminum For Paint

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  • #16
    Originally posted by H380 View Post
    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.
    Hydrofluoric acid, read the MSDS for that stuff and you'll probably be really REALLY careful!

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    • #17
      Ralph Nader--------never knew that truck/trailer loads of 100% aqueous Hf is being transported on every highway, today.

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      • #18
        I'm calling shennanagins on a metal paint not needing primer. I agree with the previous recommendations, scuff up the surface, prime and paint. Been a while since I've done any aluminium but I seem to recall green scotchbrite leaving a good surface for paint.

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        • #19
          When painting aluminum auto body and motorcycle parts I use Alumiprep. It etches the surface in a similar manner as phosphoric acid etches steel and prevents flash oxidation of the bare aluminum.

          It can be found at auto paint supply houses. Or, of course, on Amazon.

          -js
          There are no stupid questions. But there are lots of stupid answers. This is the internet.

          Location: SF Bay Area

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          • #20
            Rustoleum self-etching primer is what I have been using on small aluminum and stainless parts.Walmart carries it back in the automotive section and
            Tractor Supply also carries it.
            Degrease and rinse with hot water,air dry and spray.

            https://jet.com/product/detail/161b0...4-4ae0226ab103
            I just need one more tool,just one!

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            • #21
              One trick is to rub the aluminium down with wet-and-dry paper using the primer as the lubricant. This ensures that the paint gets right onto the aluminium, not on the surface oxide, which can't reform under the paint, as the paint keeps the oxygen out.
              Gluing aluminium together with epoxy works well if the glue is applied this way, too.

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              • #22
                Good idea! Never thought of that.

                Ummm, seems like it could get really messy, though.
                There are no stupid questions. But there are lots of stupid answers. This is the internet.

                Location: SF Bay Area

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                • #23
                  Originally posted by DATo View Post
                  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.
                  Or cover it with wood grain contact paper. Then it will blend in with wall paneling.

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                  • #24
                    I agree with a couple of other posters, looks nice natural. But if you want or need to paint it, the best, easiest way would be to nip down to your local blast finishing place. Glass beads or fine AlOx.

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                    • #25
                      Nix to that. I have tried that in the past and the Contact paper shrinks over time and leaves gaps around the edges.



                      Originally posted by reggie_obe View Post
                      Or cover it with wood grain contact paper. Then it will blend in with wall paneling.
                      Paul A.
                      SE Texas

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

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                      • #26
                        Green Scotchbrite? But there are about a half dozen different grades of Scotchbrite that are green, perhaps more. I have two of them as well as a fine one that is white. Perhaps I will try the finer green one first.



                        Originally posted by epicfail48 View Post
                        I'm calling shennanagins on a metal paint not needing primer. I agree with the previous recommendations, scuff up the surface, prime and paint. Been a while since I've done any aluminium but I seem to recall green scotchbrite leaving a good surface for paint.
                        Paul A.
                        SE Texas

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

                        Comment


                        • #27
                          So, is there any real evidence that the oxide on an aluminum surface will actually prevent paint adhesion?
                          Paul A.
                          SE Texas

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

                          Comment


                          • #28
                            Originally posted by Paul Alciatore View Post
                            So, is there any real evidence that the oxide on an aluminum surface will actually prevent paint adhesion?
                            Without being dogmatic about this, Paul, I would think that painting the oxide means that one would then be relying on the paint's sticking to the oxide AND on the oxide's sticking to the aluminium.

                            Painting directly on the aluminium, on the other hand, would seem to halve the possible failure modes.

                            As far as I know, primers for aluminium are designed to go on aluminium, and are not designed to go on the oxide. My understanding of the situation is that any paint job on aluminium must exclude atmospheric oxygen to prevent that irritatingly active metal from forming its oxide layer again. I may, of course, be completely wrong, but the foregoing makes sense to me.

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                            • #29
                              Wait, theres more than one grade of green? Ive only ever seen one... At any rate, the green that im talking about is the one they sell at loves with the sanding supplies, next to the grey and white pads.

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                              • #30
                                Originally posted by Paul Alciatore View Post
                                So, is there any real evidence that the oxide on an aluminum surface will actually prevent paint adhesion?
                                Not really... the oxide is extremely well bonded well to the the surface and hard. Anodizing first (thick aluminum oxide) is a perfect way to get paint to stick.

                                Aluminum oxide forms almost immediately the AL is exposed to oxygen and is protective for the base metal.

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