Clear the space, and prep concrete by filling any pits and holes with quick-set concrete. To do this, mix concrete powder with water until it has a mashed potato-like consistency. Use a trowel to fill the holes, and let set (a couple hours). Once set, smooth any bumps with a grinder and flat disk. Sweep the entire space, and apply a phosphoric acid wash to the floor following the manufacturer's instructions. Allow to dry overnight.