Though we do everything possible to treat cracks and do eliminate 90% of them, it is possible they may reoccur. If they do, it is usually in the form of a hairline, which is not objectionable as it is largely hidden in the texture. However, if a crack becomes too objectionable, it is easy to repair. Proper placement of tension cuts greatly reduces the chance of the crack returning. Check cracking is a natural phenomenon which occurs in rock, dried-out mud flats, paint, and concrete and in ceramic coatings. Cracks in the concrete may be structural or surface cracks. Surface cracks are generally less than a few millimeters wide and deep. These are often called hairline or check cracks and may consist of single, thin cracks, or cracks in a craze- or map-like pattern. A small number of surface or shrinkage cracks is common and does not usually cause any problems. Surface cracks can be caused by freezing and thawing, poor construction practices, and alkali-aggregate reactivity. Alkali-aggregate reactivity occurs when the aggregate reacts with the cement causing crazing or check cracks. Structural cracks in the concrete are usually larger than 1/8 inch in width. They extend deeper into the concrete and may extend all the way through a wall, slab, or other structural member. Structural cracks are often caused by settlement of the fill material supporting the concrete structure, or by loss of the fill support due to erosion. The structural cracks may worsen in severity due to the forces of weathering.