Masonry Magazine May 1971 Page. 20
Specification
The specification requires that units be composed of concrete having an average compressive strength of at least 3500 psi and an absorption averaging not more than 10 lbs. of water per cubic foot of concrete. Less restrictive requirements are listed where units are protected or not exposed to severe weather conditions.
Mortar recommended for use with these units should conform to ASTM C-270. Because of the possibility of severe exposure conditions, it is well to recognize this variable by specifying the use of Type "S" Mortar. The type "S" mortar also provides greater shear and tensile bond strength than leaner mortar.
Workmanship
Much will depend on the quality of workmanship on the job, as well as the quality and consistency of the mortar. Employment of competent, skilled and conscientious craftsmen is a must. It is encouraging to note that a prideful attitude has been observed among masons when they begin to work with customized architectural units. The creation of a monumental sculpture inspires them to improve their workmanship and treat the customized units with a spirit of accomplishing an artistic work of which they can be justly proud. They strive to put forth their best efforts and make a good showing even from the standpoint of production output.
Experience had developed certain procedures in the construction process which, while not universal or mandatory, deserve consideration and evaluation as suggestions which could prove helpful:
a. Avoid inadvertent placement in the wall of units which may have become damaged.
b. Lay the customized masonry units from inside to outside, where possible or permitted by union regulations. This minimizes cleandown on the face of the block.
c. Cover the top of the wall at the end of the day.
d. Use of innovative devices for tooling head and bed joints of units having recesses or projections has been helpful in improving appearance and efficiency. For example on a project using the fluted block as illustrated in Fig. 1, the mason tooled the joints with a piece of styrofoam which had been rubbed over the surface of a block until it conformed to the shape of the block's face. This made the job of tooling the joints much quicker and easier.
Cleaning
In cleaning it has been found advisable to avoid the use of a strong acid wash. When its use may be unavoidable it should be diluted, and thoroughly washed away with clean water. It is preferable to depend on detergents for cleaning.
Findings from on the job experience of one of our most successful producers qualifies and implements the foregoing with suggestions which can be summarized and quoted in part as follows:
Usually the color of the wall built of block as they are molded will be fairly light and flat appearing. This is due to the rich cement content and the high percentage of fines or laitance which are brought to the surface by the action of the vibration during the manufacturing process. This color can be modified by aging and erosion of the surface. This process can be accelerated by the process of sand blasting or by the use of acid or detergent cleaners. We always recommend a cleaning of some type on architectural block walls. We strongly advise that the cleaning action be of sufficient strength to remove some of the surface laitance so that the fine sands and aggregates will be exposed and contribute to the true aged color of the wall. It is good practice to buildup a sample section of the wall in the plant and use different strengths of cleaning chemicals on portions of the mock-up to illustrate to the designer the variety of effects which are possible with the same unit.
In summation as to the uses of architectural concrete masonry, it is appropriate to underscore that it is extensively prevalent as a complete structural material. Many multi story wall bearing structures have been built employing the recent innovation of "engineered" masonry design. For buildings with reinforced concrete or steel frames architectural concrete masonry is strictly competitive in cost and performance with all curtain wal material.
NATIONAL CONCRETE MASONRY ASSOCIATION
P.O. Box 9185, Rosslyn Station, Arlington, Virginia 22209