Bonding of cement based materials to masonry units substrates is an important aspect of masonry construction and repair of concrete structures. A good bond is necessary for strength and to prevent the infiltration of water between the mortar and the unit. The bond between mortar and masonry unit is a complex process involving numerous factors. In this study those factors that could be controlled before the mortar is mixed by the mason at the job site were examined. It was found that the absorption capacity of a unit is affected by the amount of pore volume and the size of the pores. Mortars with high moisture retentivity and cohesion at high water contents were found to have higher adhesion potential and better bond strength to masonry units. An increase in the cement content with its high surface area increases the fresh mortar cohesive strength and adhesion potential. Manipulation of the amount and gradation of aggregate surface area enhanced moisture retentivity and cohesion. Increasing the viscosity of the liquid in the paste helped to improve moisture retentivity and cohesion. A model for predicting the amount of liquid that would be absorbed by a unit from a fresh mortar was derived and compared to actual data. A design methodology was developed to aid in the design of masonry mortar by basing design not only on the properties of the mortar but also on its predicted behavior with the selected masonry unit.
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