If masons can't stop the cracks, the next best thing is to control them. So before the concrete dries, they deeply groove the surface to make weak spots, called control joints, so the concrete cracks at those lines and not randomly. Sometimes concrete doesn't cooperate, however. Random cracks may appear anyway. Cracks aren't the only problem you'll encounter.
Holes sometimes develop in concrete floors.
Sometimes these holes are caused by improper installation, when the concrete originally was poured. If pockets of water were left in the concrete, they eventually dry out, leaving an air pocket. These pockets easily can refill with water and freeze in cold weather, breaking out the surface concrete above, creating pop-outs. Regardless of where cracks come from, you have to repair them before you can coat the surface. Yet before you begin, you still should determine what caused them in the first place.