Hey Mark76,
Self etch primers stick to Clean aluminum, Self etch primers may stick to aluminum that may have small amounts of oxidation on them for a while. The oxidation will keep working and bubble up under the primer/paint that you just applied. It’s just a mater of time. Media blast will take off the surface oxidation but not the oxidation at a Micro level. Lots of airplanes are made of hardened/tempered Aluminum and we use an acid etch Aluma Prep 33, this gets down into the micro cracks and oclutions and cooks it out, clean water rinse then Alodine, then acid etch primer and topcoat. Extra steps in between but they only take minutes really. This process is approved for aviation optional for antique outboards but i’ll take the high road. Jim
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