Foundations can be made of stone or block and exterior or interior walls. Cracks in the foundation may come from the shifting or sinking of the foundation, and will then need to be tuckpointed. The erosion of the foundation mortar joints may come from excessive water running down the wall over a long period of time. This will result in the foundation needing to be tuckpointed as well. Good mortar on your foundation will not only keep water out but pests, as well.