Masonry Magazine October 1988 Page. 18
DESIGN
The architect's charge is to create an enclosed space to serve a specific functional need. In order to accomplish this he must provide a wall system which satisfies the structural requirements imposed by the building codes, is aesthetically pleasing and which falls within the budget limitations established by the owner. Customized concrete masonry is one of the few building materials which can satisfy all of the above criteria.
Consideration in the design of a new customized block shape involves communication between the architect and block manufacturer. The architect will decide what form the walls will take. The block manufacturer can determine if the idea can be converted into masonry shapes. Assuming that the architect wishes to achieve a particular effect, a play of light and shadows, a special wall texture, a new dimensional effect---the local concrete block manufacturer, knowing the possibilities and limitations of the block machine, can best determine how the desired effect can be achieved with concrete masonry. Detailing of customized concrete masonry walls requires special attention. The block supplier should be consulted regarding special shapes for use at corners, jambs, sills, etc.
TOP EXT CORNER PETAIL
OF BEDDI
Figure 2: Example of Special Corner Detail
Provisions to accommodate differential movement needs particular consideration because wall cracking due to thermal or moisture movement, while not structurally serious, will affect not only the aesthetic quality of the wall due to unsightly cracking, but also the weathertightness of the wall itself. Wall movement is controlled by horizontal reinforcing steel used in conjunction with control joints. Horizontal steel, either in bond beams or as joint reinforcement, increases the tensile resistance of the wall. The use of horizontal joint reinforcement in wythes consisting of concrete brick or thin masonry veneers is especially critical and it is in these locations where it is most often omitted.
As a next step, it is necessary that mock-ups or models of the design be prepared so that the architect can visualize the effect of light and shadow on the wall. Curved surfaces produce more subtle variations of shade and shadow. Angles on the surface will produce sharp shadows and highlights; a split block texture produces combinations of both.
Once the feasibility of a new customized concrete masonry unit is established, there should be close communication between the block producer and architect during the design phase to help minimize the number of special shapes required and to maintain modularity.
It is essential that a sample panel be built prior to commencement of the actual construction. The primary purpose of this panel is to make the architect aware of the range of variations in color and texture among masonry units which is an inherent part of the manufacturing process. The panel should be made so as to illustrate the extremes which may be expected over the duration of the job in order to eliminate the possibility of work stoppages, delays and possible litigation at some later date. The panel may be located either at the producers yard or, preferably, at the job site. At the job site the panel is a good source of reference during construction and helps to minimize problems of workmanship, type and color of mortar and other factors. It can also be used to test various washes and clean down procedures. The final appearance of customized concrete masonry is affected by various cleaning processes.
WORKMANSHIP
Good workmanship is as essential to the satisfactory performance and appearance as any of the other ingredients of a customized concrete masonry wall. The fact that architectural units are designed for their aesthetic qualities and require special attention to place them in the wall so that the desired results will be achieved cannot be over emphasized.
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 re-laid 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 joints are not always feasible. In these instances the mortar joints, of necessity, must follow the contour of the units to prevent the formation of ledges upon which moisture may accumulate. Special attention must be accorded these joints to assure that proper bond is accomplished between the mortar and the units.
Another important detail involves controlling or excluding moisture from the masonry wall. Proper installation of a permanent flashing material is recommended at points where the masonry wall is vulnerable to moisture penetration. Wall flashing is installed to collect moisture that may penetrate the wall and divert it to the exterior, generally through