Questions about painting cement Porches

I have 2 cement porches that were both painted in the past. When I power washed the front porch in order to get it clean for repainting, most of the paint came off. The other porch, the paint remained virtually intact.
Do I need to use muriatic acid to clean the cement? TSP? Or can I use a good cement primer and then paint? Humidity is high where I live, do I need to wait for a few days before priming since I just power washed this weekend?

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