It should be noted that it can be important, particularly when using masonry strips in clay or silt sub-strata, to bed the masonry units in mortar and to completely ﬁll all joints.
The reason for ﬁlling the joints is mainly to prevent the strip footing acting as a ﬁeld drain with the water ﬂowing along the surface of the formation level and through the open joints of masonry. The authors have found clear evidence of induced settlement due to softening of the clay surface below dry random rubble strips (dry random rubble being a term for dry stacking without mortar and not dry meaning no moisture).
Fig. 9.3 Masonry strip footing.