Masonry foundations, like masonry and brick walls, are also somewhat permeable. However, even more than the wall above ground, the foundation below ground is often exposed to even more moisture. From area to area, sub-grade earth has different levels of moisture, but soils usually contain a high degree of moisture. This means the somewhat permeable foundation is exposed to that sub-grade moisture, and that foundation does something surprising. The foundation, through the capillary action of water will actually wick water upwards. That is counterintuitive because we think of water as naturally flowing downwards, but in some cases water will actually wick upwards. When this happens in masonry walls, we call this phenomenon Rising Damp.
To stop Rising Damp, modern building Code requires the installation of a Damp Proof Course (DPC). In modern masonry construction, a DPC is built with a low permeability or impermeable material such as a bitumen roll membrane or synthetic roll membranes. In the times of historic construction they did not have technologies such as polyvinyl or modified bitumen. Nonetheless, even 100+ years ago, builders were aware of the phenomenon of Rising Damp, and to deter Rising Damp they often used slate tiles embedded directly into the mortar joints at a specific location, usually above the splash-back zone.
This means that the area below the DPC is often exposed to some degree of rising damp. Rising Damp will cause accelerated deterioration of the lowest mortar joints in a brick wall.
The image below shows an example of foundation waterproofing, and area which will be buried underground in the future after construction.