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I have seen it done and seen the paint last if cleaning is thorough and the proper paint is used but the first answer is true. You won't replicate a factory finish and it is nore difficult to do than a wood window. The paint finish won't look as good but from a short distance its ussually not noticeable. We use alcohol to clean surfaces prior to painting to get a good clean surface. With metal the temperature needs to be ideal also. Not too hot, not too cold.
Jon Brewer
Dear C E,
I would leave the window alone. Aluminum windows are typically electro statically painted in a controlled environment when they were originally built at the factory. This environment includes air cleaners, pressure sprayers, heat/infrared curing ovens and lots of air handling equipment (large fans). This controlled environment leaves your aluminum windows looking like brand new car paint finishes. It is nearly impossible to replicate such an environment in the field at your home thus leaving many people with unhappy results when they try to repaint aluminum windows after they have been installed. The weather effects and pitting you describe make this process almost impossible. I believe you will be in for a lot of work and frustration and not happy with your end result if you try such a task.
Sincerely,
John Patrick
President, Larmco Windows, Inc.
Aluminum windows are not energy efficient and they are noisy. If the window is more than 10 years old, replace it with an energy star rated vinyl window that has bronze outside/white inside. It will look better, be quieter and the energy savings will pay you back in a very short time.