A photograph of a red brick wall on a rainy day. Wet concrete paving slabs are in contact with the wall, only one brick below the slate damp-proof course.

1. Damp proof course (DPC), bridged by mortar.
2. The path should be two bricks (150mm) below the DPC.

A DPC is a physical barrier to prevent ground water rising through a wall. This DPC has not failed and does not need replacing. Mortar is bridging over the DPC, which lets moisture move around and over the DPC, up and through the solid wall.  

Also, rain is splashing off the hard pathway and back onto the wall above the DPC.

Source of moisture: ground water and rainwater.  

Repair: remove the mortar bridging the DPC, check for and repair any leaking guttering at roof level, and lower the path if possible.