An experimental investigation of compressive failure in masonry made of soft clay bricks is presented. Masonry assemblages are tested to evaluate the influence of the relative strength of mortar on the observed damage evolution and compressive failure. Damage evolution associated with the formation and propagation of vertical splitting cracks during the compressive load response of masonry assemblages in the stack bonded arrangement are studied using a full-field optical technique based on digital image correlation. Using image correlation, clear evidence of the crack forming in the mortar and propagating into the brick is established. Damage is associated with cracking in the mortar due to lateral tension produced by the confined expansion of brick. Failure depends upon the tensile strength of the mortar. In mortar with lower strength than the brick unit, failure is produced by spalling associated with multiple cracks, which results in a loss of load bearing area. For mortar with a higher strength than the brick, cracking occurs when the level of compression is a significant proportion of the compressive strength of the brick material. Localized crushing resulting from localization of strain in a small region at the brick–mortar interface is produced at axial stress close to the unconfined compressive strength of the brick material. Failure in the case of high strength mortar is a result of the localized crushing and the resulting global instability. © 2016, RILEM.