Cracks in concrete walls are usually caused by concrete shrinkage. While they may not be aesthetically pleasing and can cause some issues, they don't necessarily mean that your home's foundation is in danger. As concrete dries and hardens, it shrinks and tends to crack into square sections; this is why control joints are used on sidewalks to provide weak spots where the concrete can crack without compromising its strength or safety. If cracks appear shortly after the concrete has been poured, it could be a sign that the mixture was not properly prepared or that it was poured too quickly.
Step cracks are similar to diagonal cracks, except that they occur in concrete block basement walls while diagonal cracks occur in concrete walls. It is important to remember that all concrete will crack and that most of these cracks are harmless. This is because the concrete from different trucks may have a different color, and because the first load of concrete was held for a while, a line may appear 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 understandable to be concerned if you notice cracks in the concrete.
As the concrete contracts during the curing process, vertical cracks form in the concrete or block, some so small that they are barely visible. A more serious vertical crack can occur when construction contractors do not properly prepare the concrete foundations or when there is inadequate steel reinforcement when workers pour the concrete for the wall.
