We recently had to remove the carpet and padding from a basement room that's had repeated water entry - nasty stuff! I'd like to seal and paint that floor, but it's in really poor condition. The previous owners apparently attempted to level the floor before installing the carpet, but whatever they used is very rough, dusty, and even crumbling at one edge. And the floor is still far from level! What do I need to do to prepare this floor to be painted?