If your paint doesn't seem to be sticking to the concrete, it's likely due to atmospheric conditions. If there's a lot of humidity, the paint won't want to stick, and it won't want to dry well, either. \
Moisture that is seeping up from the ground, or damp concrete, will also make it difficult for paint to stick. \
Apply one or two coats of primer and allow them to dry thoroughly. This will make it easier for the paint to stick to the concrete. \