Painting aluminum castings problems and questions.

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Guys. I always "sand" blast my castings using fine to medium glass before using an etch primer and then a spray coat of colour. If you want to use a clear coat then that seems to work well on the blasted surface with no etch. Blasting gives a pleasant uniform colour to all metals - I am a fan!
I started making custom car badges a few years ago. I machined them from thin aluminum plate and TRIED to get paint to adhere. I tried every type of paint, including the super durable, made for car wheels, won't chip, sticks like you know what to a blanket. I couldn't find anything that I was happy with. Yes, some did adhere fairly well, but not good enough. That's when I got into powder coating.

For those that aren't familiar with it, as I wasn't when I started, it is fairly easy and inexpensive to do. I bought a gun and some powders from Eastwood and a cheap toaster oven from Walmart. You need a compressor, and that's about it. It is super durable; you basically can't scratch it off. If you don't want the whole part coated you can mask it (high temp tapes are available) or sand areas off after coating. The stuff is not easy to sand or remove, but is by far the best coating for aluminum I've ever used. I use it often now on parts I make that I would otherwise just leave bare aluminum as it is so easy to do and looks great.

A motor mount for a Taig lathe powder coated:

Screenshot 2023-03-22 at 8.07.16 PM.jpg

A couple badges, hot out of the oven. These were coated with black, baked, the surface sanded off to leave the black in the machined areas, then coated with clear and baked again:

Screenshot 2023-03-22 at 8.07.57 PM.jpg

I've been using a product called Gun Kote (available in many colors on Amazon) on aluminum with no issues. A potential downside for some is that it must be cured at 300F for an an hour. I bead blast aluminum surfaces so the paint can get a "bite". As far as cleaning goes, I found what works best for me is to spray Simple Green on the part after bead blasting and then scrubbing the part with ordinary Dawn dish soap before rinsing with warm water. I immediately dry the part with compressed air as our water is pretty hard and will leave deposits if allowed to air dry. Dish soap is remarkably good for removing grease and cutting oils. I use these same cleaning steps before anodizing and plating. - Terry
I have to go along with Terry's recommendation of Gun Kote. Grit blast with 120 aluminum oxide grit, wash clean with detergent, then spray it on. I use a cheap air brush at 15 to 20 psi. No primers needed for any base metal like aluminum or brass. If you mess up your paint application just wash it off with acetone and start over. However, once you bake it, the only way to remove it is to grit blast it again. I haven't found a solvent yet that will soften, remove or discolor it. Unlike regular paint Gun Kote is very thin and requires building up the finish in thin coats. 3-4 coats are adequate. If you don't like the color after baking it you can repaint with another color right over the previous baked finish. No grit blasting required. It sticks to itself very well, it just needs a detergent cleaning to repaint it with more Gun Kote. It is a very tough finish and goes on thin so as not to cover up detail or interfere with close fitting parts. It is available in gloss, satin, and flat finishes. I prefer satin and flat finishes for model engines.

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