Cracking is a natural propensity of concrete. Concrete is a liquid when it is initially poured. It solidifies into a solid over a number of days, shrinking as it does so. Within the first few days after installation, this initial shrinkage frequently results in hairline cracking. As the concrete continues to cure, it will continue to harden and shrink, causing further cracking. Concrete cracks can be caused by many different factors. The main cause of cracking is temperature change. When the temperature changes between day and night, small cracks may form in the concrete as the building settles or moves. Large cracks may also form if the foundation is not stable. Cracks may also form if there is a lack of moisture in the concrete. Too much humidity inside the house may cause the walls to expand more than expected, which could lead to wall cracks. Concrete cracks should be repaired before they become larger problems. Hairline cracks can be filled with epoxy putties or other resin-based materials. Larger cracks may require replacement of some of the concrete or reinforcement within the concrete. The type of repair required depends on what caused the crack in the first place. Concrete floors are susceptible to another type of damage too: stains. These can come from many sources such as oil or wine that are spilled on the floor or furniture that is stained with paint or ink.