It is extremely important to determine the type of foundation crack you are dealing with before doing any type of repair. The first type of crack is a cyclical , which means the crack opens and closes with the change of the seasons. Cyclical cracks can be repaired with a urethane foam to allow movement in the foundation but still provide a water tight seal. The second type of crack is progressive and these type of cracks will continue to get larger unless something is installed to stop future movement. Progressive cracks are typically injected with structural epoxy and are often combined with steel staples to prevent separation. Structural epoxy is a rigid material that is typically stronger than the surrounding concrete which creates a tight bond inside the crack. If the wrong material is used to fix a foundation crack it can end up costing you more to repair in the long run, so make sure you have a qualified professional diagnose your foundation!