Adhesion of Masonry Coating: Effect of Mortar Consistency and Type of Substrate

Abstract

The longevity of masonry mortar coatings is heavily influenced by their adhesion to the underlying substrate, a factor determined by multiple parameters including the nature and thickness of the mortars, as well as the substrate type and surface condition. This study explores the influence of cement mortar consistency (fluid, plastic, and firm) and thickness on adhesion to two distinct substrates -concrete and breeze block. Adhesion was evaluated using shear tests on 50×50 mm 2 specimens. An adhesive failure mode was observed at the interface between the substrates and the coating mortars. Among the tested conditions, plastic consistency mortar demonstrated superior adhesion to both substrates, with breeze block exhibiting a higher degree of mortar adhesion compared to concrete. This effect was particularly pronounced at early stages, with differences ranging from 35% to 257% at 7 days, reducing to 8% to 92% at 28 days. An increase in adhesion with thickness was observed for all mortar types across both substrates, with plastic consistency mortar displaying the most significant increase, exceeding 100%. The fluid and firm mortars showed comparatively smaller increases, ranging from 8% to 67%.