A common item in Philadelphia homes that I repeatedly comment on is the stone foundation. Unlike concrete foundations, which require little maintenance, stone foundations require regular care and re-pointing to prevent movement and deterioration. Stone or rubble foundations are comprised of many smaller units, often limestone blocks, which are held together with mortar. This method of foundation construction has been found to be very durable, however seepage is a very common. At some point it can be a problem. Another issue is the deterioration of the mortar over a period of many years. This can occur on the exterior, above or below grade, or on the interior of the foundation walls. This deterioration can lead to large gaps between the stones. In some cases this can lead to structural issues or constant seepage and moisture intrusion. In other situations there may be little structural movement. In most cases it takes many years to occur. If left unchecked it will most certainly develop into structural issues. The stone foundations were very common around WWI. Most of the older homes in Philadelphia are stone foundations and will require additional maintenance.
So now what? If there is no evidence of your foundation moving or shifting, foundation walls may need to be repointed. It is labor intensive, but fairly inexpensive.
If you are walking through your home and the floors are sloped, the walls are leaning, foundation is bowing, obvious signs of stone collapsing, you may have further underlining issues. It is always best to contact a professional for advice.
An issue that should be looked at prior to repointing your stone foundation is the water intrusion. As mentioned earlier water seepage is very common in stone foundations. If you are unsure if you are having water issues, I would recommend calling in a water proofing expert that specializes in stone foundations. A water proofing system is fairly expensive to install and in some cases can lead to more expensive repairs. After the dirt surrounding your foundation wall is removed, all that loose mortar that has been compacted between the stone joints may crumble. You may now need to repoint your exterior foundation below grade.
After all repairs/maintenance is complete, it is always highly recommended to continue routine maintenance on stone foundations. Put the mortar back between the stones where it belongs.
Certified Home Inspector