They are usually caused by concrete shrinkage. While they can look unsightly and cause some problems, as mentioned above, they don't immediately threaten your home's foundation. When concrete cures (dries and hardens), it shrinks and wants to crack into relatively square sections; that's why control joints are seen on sidewalks to provide weak spots where concrete can crack without affecting aesthetics, strength, or safety. If cracks appear soon after pouring the concrete base, it is possible that the concrete was mixed poorly or poured too quickly.
Step cracks are very similar to diagonal cracks, except that step cracks occur in concrete block basement walls and diagonal cracks occur in concrete walls. ALL concrete cracks and you should understand this problem and realize that most concrete cracks are safe. Because the concrete comes from different trucks, it has a different color, and because the first load of concrete was held for a while, the appearance of a line appears between the two different loads. Your home's foundations, the concrete walls surrounding a basement or low-rise space, support the full weight of the house, so it's natural to worry if you discover cracks in the concrete.
As the concrete contracts during the curing process, vertical cracks form in the concrete or block, some so small that you can barely see them. A more massive vertical crack can occur when construction contractors improperly prepare concrete foundations and when the wall had poor steel reinforcement when workers poured concrete for the wall.
