SCINFERNL
+1y
Muriatic Acid will clean anything off that paint would have a problem sticking to. Then a simple hose down, squeegee and 24 hours of drying time should make it ready for paint. Follow whatever instructions you have for the paint you will be using, since it may require a primer/sealer first - concrete is porous and may suck the paint down quite a bit before you get a uniform coat...