A stress crack is a crack in a surface caused from stress or the settling of building materials. In a wall, it is often the result of the building's foundation settling. In a vehicle's windshield, a crack can be the result of too much chassis twisting while negotiating a hilly or bumpy surface or when applying too much power to the tires in high-performance applications. Most stress cracks can be easily repaired, but some are a sign of a much more serious problem yet to come. In brick buildings or cement block foundations, the sight of a crack caused by stress is not uncommon. Through years of settling, the building will begin to flex and twist, often showing up as a crack in the mortar. In some severe settling, actual bricks will crack in half as the settling advances and becomes more severe. This most often happens around and over windows and doors. In some poured cement walls and barriers, large cracks can be found as the footings settle and move. These seldom penetrate all the way through the concrete wall, but they can cause the wall to break apart and fall in severe cases. The use of reinforcing wire and steel rod often help the concrete to resist succumbing to a stress crack.