Many dams constructed during the 20th century used concrete as construction materials for walls, spillways and intake / outlet structures. For these types of structures, regular inspections should identify any problems such as cracks, spalling, surface deterioration or, in some cases movement, tilting or undermining. Small cracks or other forms of deterioration are not usually a major tack to correct if found and mended in the early stages. If left unresolved, water and sediment can worsen the problem especially in colder weather with frost jacking. Other, more serious issues such as spalling, missing or compromised concrete or movement of a structure are a more complex repair