Do you know why some dampproofing holes in the brick and some in the masonry joints? 

Damp Sam looks tell why the old method of damp proofing drilled and injected into the brick and the new method goes into the joints of the mortar. The damp proof cream lines the pore of the masonry stopping moisture tracking by changing the shape of the meniscus of the water. Some laborers in the 80s & 90s were told to use the high-pressure systems incorrectly leading to a break down of the damp proof course.