Masonry Magazine October 1988 Page. 17
NCMA-TEK
TEK 40
CUSTOMIZED MASONRY WALL CONSTRUCTION
INTRODUCTION
The concrete masonry industry, which only fifty years ago offered a limited selection of less than 30 different block types, most of which were utilitarian, today produces over 1400 units of various size, shape, color, texture and surface treatment. Much of this increase is due to the advent of architectural or "customized" facing units designed to provide a wall having a finished surface without the addition of opaque coatings or treatments which would appreciably alter its appearance. Among the more popular units are those with projecting ribs or flutes; those with surface textures created by splitting, grinding, or use of vertical striations; and those which "slump", creating the appearance of adobe brick.
Walls requiring no additional surface treatments or finishes may now be built as exterior or interior bearing or non-loadbearing walls, may be designed of "through-wall" units where only one thickness (wythe) of masonry comprises the wall section, may consist of architectural units used as veneers backed up with concrete masonry or other materials, or the exposed units may form the facing portion of a structural composite or cavity wall. Attractive and interesting walls, coupled with the economy, strength and durability of concrete masonry are now a reality.
The same variables that influence the performance of any masonry wall: materials, workmanship and construction details, must be granted more through attention when using architectural facing units. This is particularly true for exterior single wythe walls where water repellent sealers are not specified, walls constructed of specialty units which do not permit the use of properly tooled joints and veneers which may be more susceptible to cracking due to their physical features and methods of attachment.
MATERIALS
MASONRY UNITS
The physical properties of architectural facing units needed to assure good performance in the wall are dependent upon a number of factors. Presently there is no ASTM Standard which specifically applies to these units. In the absence of such a standard, experience has shown that the strength and absorption requirements of ASTM C55, Standard Specification For Concrete Building Brick, Grade N, Normal Weight, are best suited for architectural veneers and facing units used in exterior walls or where high strength and resistance to moisture penetration and severe frost action are desired. However, the requirements for permissible dimensional tolerances are not applicable to certain customized units. These requirements are intended only for formed surfaces and should be waived for units having rugged or uneven faces, such as split faced and slump units.
MORTAR
Experience and research have indicated that when masonry walls permit the passage of wind-driven rain, the reason can often be attributed to faulty mortar joints. Because of its strength, workability, bonding characteristics and the possibility of severe exposure conditions, Type "S" mortar is recommended for use in customized masonry construction. It is important that once the mix proportions and materials are established, they are maintained throughout the job. Variations in the 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.
Figure 1: Split Ribbed Units Add Form and Shadow to Angles and Soft Curves