The construction of masonry walls begins with a leveling layer of type III standard mortar, 1 to 3 cm thick, or with a grade course of special Sand-Lime Base Brick, laid in type III standard mortar. The leveling layer acts to straighten the surface of the wall, creating level vertical and horizontal surfaces, and compensating for any height irregularities on the surface of the concrete slab. The leveling layer must be worked in thin-bed mortar, which is included in the scope of delivery in the form of drymix mortar. The leveling layer must be sufficiently hardened before the remainder of the wall is built. The cross-jointing can then be safely and efficiently carried out on the wall.