Masonry Magazine May 1972 Page. 14
Tooling
The Standard Specification for Concrete Building Brick, is applicable to solid concrete veneer and facing units larger than brick size such as split units, and is often referenced for minimum requirements for customized units. In general, manufacturers of these units promulgate specifications which are significantly more stringent than current minimum ASTM requirements for concrete masonry, in order to assure that the end product will have sufficient density, water imperviousness, and durability to function as the exterior facing with no waterproof coating.
Mortar
Because of its properties of strength, workability, bond, and possibility of severe exposure, Type "S" mortar, ASTM C-270, is recommended for use with customized concrete masonry construction. It is important that the mix proportions and materials once established, be maintained throughout the job. Variations in mortar as the job progresses can markedly change the appearance of portions of the wall, sometimes creating the impression that the units have changed in color. Measuring boxes can be used to control the volume of sand, but care must be taken to note changes in moisture content which cause "bulking" and affect the weight of dry sand in a given volume of damp sand.
Workmanship
The masonry wall composed of facing units is most often used as the exterior of a building and thus is required to provide resistance to rain. Given proper masonry units, mortar, and construction details, good workmanship is the remaining essential ingredient in assuring resistance to water penetration. Experience and research have indicated that faulty mortar joints contribute substantially to leaky walls. Faulty mortar joints can occur from moving or adjusting a unit after the mortar has stiffened. Unless the unit is adjusted into final position in the wall while the mortar is still soft and plastic the bond between mortar and unit will be broken causing a fine crack where wind driven rain can penetrate. Adjustments needed after mortar has stiffened should require that old mortar be removed and the unit relaid with fresh mortar. In multi-wythe, or composite wall construction, resistance to rain penetration can be achieved when the collar joint (vertical joint between wythes) is filled with mortar. This may be done by back parging the facing or backing wythe or by pouring fine grout into the collar joint.
Another vital element is proper tooling of the mortar joints on the exterior side of the wall. The joint should be concave, tooled with a jointer that is slightly larger than the width of the mortar joint so that complete contact is made along the edges of adjacent units. This compresses and seals the surface of the joint and is particularly important in achieving good performance where the wall is composed of one unit in its thickness.
Because many of the architectural facing units have curved, fluted, or ribbed surfaces, conventional joint tools used by masons for plane surfaces are not always adaptable and other, more effective and efficient devices have been developed to produce good joints. Fig. 1 shows one example of an innovation developed for tooling vertical joints on a wall of split ribbed units. Other devices to assist in better workmanship include wooden rakes with tines (wooden dowels) spaced to fit into the recesses of a ribbed or fluted unit. Use of this rake enables the mason to efficiently remove mortar which has squeezed into the spaces between ribs or flutes.
Construction Details
Construction details with customized concrete masonry must result in a wall which will satisfactorily accomplish at least three functions: structural adequacy, protection against adverse environment; and it must satisfy the esthetic objectives sought after. Structural ade-