Some early concrete mixes were made by hand on the construction site. Very often these concrete mixes did not contain an adequate amount of cement to prevent premature weathering and deterioration. This was most likely because the cement was, and continues to be, the most expensive part of a concrete mix.
The weathering and deterioration appear as the sand and gravel in the concrete mix become loose on the surface of the foundation wall. Sometimes it is very easy to remove the loose material and dig through the surface of the wall. We have seen cases where it is easy to remove the material all the way through the foundation wall.
Often times we will find “seams” within an older concrete foundation wall which are weaker and more weathered or deteriorated than other parts of the foundation wall.
If the level of deterioration is not too severe, it may be possible to clean the concrete surface and patch it with specific materials designed for patching concrete. This may not be a permanent repair for the foundation wall but will extend the service life. If the deterioration is significant, the walls may need to be removed and replaced.