Masonry Magazine August 1978 Page. 19
Variables Affecting Mason Productivity
Many variables affect mason productivity, some of which are under the mason's control, but some actually increase quality. It is interesting to note that masons have no control over any of these variables, which in total affect their productivity to a degree that makes their own motivation relatively insignificant. Those concerned with mason productivity should investigate the unnecessary limitations placed on that productivity by the designer and the contractor. Bricklayers' unions have often been erroneously accused of conspiracy to limit by quota the number of brick a union mason may lay during a day's work. There is no published evidence to support the allegation. Bricklayers generally have been most receptive to innovations in tools, materials, and prefabrication, although there are some local exceptions, i.e., refusal to accept corner poles on commercial work by some union locals.
American Mason Productivity on the Rise
Mason productivity has increased 40% in the U.S. in the last 60 years, due principally to improved material handling techniques. In 1910 the ratio of bricklayers to hod carriers ranged from 0.67 to 1.5. Today that ratio is typically 1.7 to 2. In 1906 normal mason productivity was 400 to 500 face brick laid per 8-hour day. Today 570 to 700 is normal for the same quality of work. Depending on typical design variables, mason productivity might reasonably range from 200 to 1,200 brick per day. It may be indicative of the work effort of bricklayers that 21% of their work injuries are due to overexertion.
There is also the fable about the Old World craftsman, who is supposed to do everything better. Mason productivity in the United States in recent years is at least 10% higher than in England. In a recent year standards required of masonry workmanship were higher in the United States than in Switzerland, a nation world-renowned for the quality of its craftsmen.
Normal mason productivity may be defined as the number of standard modular face brick laid per hour from fixed scaffolding in a single wythe in 1:1:6 (type N) mortar, in % in. (1 cm.) concave tooled joints, in common bond, during normal spring and fall weather with normal work observation (inspection) and with normal contractor efficiency. A 1972 survey of 36 union mason contractors in 12 major cities, geographically well distributed in the U.S.A., indicates that normal mason productivity is 85 brick/hr. with a standard deviation of 20 brick/hr.
These data indicate no significant difference (at the less than 5% level) in productivity between cities. Deviations are attributed primarily to contractor efficiency. The mean value was not weighted by contractor construction dollar volume. Since it is probable that more efficient contractors collectively do more work than those of less efficiency, it is probable that the true mean value is greater than 85. Normal mason productivity without the variable of contractor efficiency is said to have a coefficient of variation of 7.5 percent.
Mason productivity is maximum at about 75°F (24°C) at 60% relative humidity. Any air movement up to about ten miles per hour (16 kmp hr.) improves productivity during hot weather. Bricklayer productivity declines more rapidly with temperature increase than with temperature decrease from 75°F (24°C).
Masons may work in the open with salamander heaters at temperatures as low as 20°F (-7°C). When wind velocities are above 15 mph (24 kmp hr.) and temperatures are below 25°F (14°C), windbreaks should be provided to protect masons. Masonry should not be laid without protection at temperatures below 40°F (4.4°C), at which temperature the ratio of mason productivity to that at 75°F (24°C) and 60% relative humidity is 0.6. Values for the weather relative mason productivity for any month of the year at any location in the 48 contiguous United States may be found in reference 15.
Computerized Estimates
Masonry construction operations, specifications and quality control are well described in the literature. Although there are several publications useful in estimating masonry costs and some annuals which provide national and regional average unit costs for several types of masonry walls, none include all of the variables which significantly affect masonry costs and none provide a rationalized mathematical model. Such a model used with a programmable calculator or computer would provide an accurate and rapid means for determining the economic effect of many alternative aesthetic and structural design decisions regarding masonry.
Following several years of research on mason productivity, the writer developed a mathematical model for estimating the initial construction cost to the owner of brick and/or concrete masonry walls and rectangular columns based on 48 input variables. The model is fully described in reference No. 17. The validity of a Fortran computer program based on the model was verified by comparison with bids by several mason contractors on a hypothetical project. The difference between the labor and materials cost estimate made by the largest and most experienced local mason contractor and the computer-prepared estimate was 2.3% over the contractor's estimated cost of $150,656.
The accompanying computer Table 1 lists project description input data. The program requires additional input data for each wythe of each wall type in the project. Computer Table 2 lists these input data for wall No. 1. Computer Table 3 provides output data on each wythe of wall No. 1, including materials quantities, wythe cost, and construction time requirement. Computer Table 4 provides output data for wall No. 1, summarizing material quantities, unit wall cost, total wall cost, construction time and crew size. Tables 2, 3, and 4 are repeated for each wall type in the project. In this example, wall No. 1 is an exterior cavity wall and wall No. 2 is a 4 in. interior concrete block partition. These are the only two types of walls in the project. Computer Table 5 provides output data for the whole project, summarizing total material quantities, project masonry cost, total construction time requirement, and project man-hours and cost per sq. ft. of building floor area. Readers interested in the program may obtain further information from the writer.
Conclusion
Bricklayer productivity can be at least doubled any time the design professions and contractors decide to do so. The reasons they have not and probably will not do so are twofold, i.e., 1) they lack economic incentive as long as the consumer is willing to pay for inefficient design and inept work rule bargaining; and 2) it is easy to blame low levels of construction labor productivity on "the unions."
Computer cost estimating can reduce contractor overhead by reducing the man-hour requirement for estimate preparation and can, therefore, increase contractor profit or reduce masonry cost to the owner and thereby increase the volume of masonry work. Because computer estimates can be prepared at less cost and in a shorter time, they can be useful to architects in comparing masonry design alternatives.
Acknowledgements
The writer is indebted to many students and clients, who by their probing questions have contributed much to the writer's understanding of masonry problems. Significant contributions were made to this paper by Richard L. Saunders, Jr., a student who wrote a Fortran program for the writer's mathematical model for estimating masonry wall and column costs.