Abstract: The invention relates to a system for applying mortar to a row of masonry units and provides for the use of a pair of supporting structures between which a straight beam extends. The straight beam allows to build consecutive rows of masonry units along a vertical plane. A mortar dispensing container is supported by rollers which move along a top surface of a masonry unit, the container being provided with a pair of elongated slots, through which mortar is dispensed in uniform ribbons.