Traditional Masonry Archives — Restoration Case Study

Traditional Materials & ASTM Standards

The building boom from 1880 to 1900 opened a new chapter in the history of material specifications. Locomotive builders, steel rail producers, and steam engine builders who began using materials such as Bessemer steel could no longer rely on craft experiences of centuries past. New technical expertise was required. Several large United States steel manufacturers attempted to implement their own ideas to produce better steel, but these efforts never made it to the marketplace. The added cost of producing better products was thought by the management of these large companies to not be worth the price of losing market share.

Above and top of page: Train Wrecks, (between 1897-1901) Dayton, Ohio. Wilbur & Orville Wright Papers Courtesy of Library of Congress Archives

As a result, the U.S. manufacturers continued to produce large volumes of steel at the lowest cost possible, believing that this is what the customers wanted. Not surprisingly, numerous quality problems with steel rails came to light through independent investigations into derailments. In fact, American steel rails were so poorly made that many railroad companies preferred British imports, which were far more expensive but much more reliable.

Resistance to standards
It was clear something had to be done. Some type of standard material specification was needed. Progress was nevertheless very slow in coming. Manufacturers in the construction industry objected to standardized material specifications and testing. They feared that placing strict quality controls on products they produced could make customers more inclined to reject items and default on contracts. Material standards were thus not well received and remained very controversial.

In a creative effort to overcome antagonistic attitudes towards industry material standards, Charles Dudley, a research chemist working for the Pennsylvania Railroad, suggested the formation of working technical committees to discuss testing methods and approaches. He further suggested that decisions on standards be based on a consensus process.

Pennsylvania Railroad Surveyor (1915) Chicago Daily News Courtesy of The Chicago Historical Society

ASTM is born
Dudley’s suggestions were finally embraced, and the American Society for Testing Materials (ASTM) was chartered in 1902 in Philadelphia.

In its bylaws, ASTM dedicated itself to “the development and unification of standard methods of testing, the examination of technically important properties of materials of construction, and other materials of practical value, and also to the perfection of apparatus used for this purpose.”

ASTM refined its consensus-building process in its early years. The key was to balance voting membership between manufacturers and users of materials in the technical committees. To allay old fears that manufacturers would dominate the standard-setting process, ASTM’s rules stipulated that manufacturers could not outnumber buyers on a specific committee. In addition, a manufacturing representative could not serve as committee chair on a standard published through ASTM. This protected the standard publishing process from unfair business practices.

Architecture Designed & Built 1880-1910
The challenge facing architects and engineers was the quality of the specified products. The pressure to deliver a finished building in a shorter period of time from design to completion pushed architects and engineers to get work done faster. This meant tighter schedules, more demanding clients and the possibility of not getting paid. Also, some manufacturers were indirectly forced to produce their clay and mortar products faster to meet growing market demand. Clay and mortar ingredients during this time already varied in quality due to the nature of the manufacturing processes and raw materials. These industry challenges, along with some growing market pressure for production, gradually affected masonry building material quality. Masonry products, especially those produced in great quantities, became more unpredictable. Materials didn’t improve until the marketplace demanded a change. ASTM was instrumental in helping make that change.

ASTM formed several new technical committees that expanded the organization’s scope beyond steel and into the masonry industry by forming Committee C1 on Cement, Lime and Clay Products in 1902.

New York Times Building under construction, New York City, NY (1903) Detroit Publishing Company Photograph Collection Repository: Library of Congress

Portland cement
The American cement industry, which traces its origins back to the 1870s when David Saylor received the first U.S. patent for portland cement, underwent major growth during the late 19th century. The first concrete road was poured in Bellefontaine, Ohio, in 1891, followed by the first concrete high rise, built in Cincinnati in 1903.

Despite its remarkable early success, however, the cement industry suffered from a lack of basic standards that defined the material’s performance criteria. The lack of basic understanding of the chemical composition and performance of portland cement led to conflicts between manufacturers and their customers. Those conflicts resembled problems that were apparent in the steel industry.

Prior to 1900, there was no consensus on the production process of the exact ratio of stone, silica, iron, and aluminum in portland cement, or on simple properties such as tensile and compressive strength. As a result, construction companies often purchased cement that was questionable in quality — not meeting performance requirements of a particular project. Robert W. Lesley reports in his 1924 book, “History of the Portland Cement Industry in the United States,” that between the years of 1871 and 1899 portland cement accounted for more than $30 million in sales of 18,841,834 barrels of product. However, it is not known for sure how many projects were actually completed with portland cement during the time period between 1872 and 1900.

Lime
By 1905 there were 1,200 lime factories producing lime products for the building industry. Some plants were small, some large; some were fired with wood, some with coal. Some used bottle kilns, others used rotary kilns, and still others used vertical shaft kilns. Some produced lime using high-calcium limestone, others dolomitic limestone. Lime products varied from region to region, manufacturer to manufacturer, causing confusion for the specifier and inconsistency in final products.

Indeed, a material standard was needed for the oldest of building materials. The ASTM C5 standard specification for lime putty and ASTM C6 for hydrated lime were published in 1906. The lime industry later moved to support the formation of its own Committee C7 on Building Lime in 1912. The committee wasted no time in publishing five more lime standards in the same year.

Lime products also had quality problems that were well-known to the craftspeople who used the material. Unlike the new portland cement, where experience and attitudes towards the product were still being established, the lime product industry had the benefit of time in weeding out inferior manufacturers. The five standards published in 1906 further helped to rid the industry of low-quality lime manufacturers.

Architects helped to bring higher-quality masonry materials to the architectural market by simply using the ASTM standards and referencing them in their specifications. When filling an order for a lime product that would meet the new ASTM standard, a lime manufacturer had to face the decision whether to continue to produce his lime products outside the standard or invest in plant operations to improve production methods with new equipment. It took many years, but as architects began to embrace the new standards, it became more difficult for low-quality manufacturers to remain in business.

Mortar testing before ASTM
Testing masonry materials for durability and performance has been going on for some time. It is important to study and test the materials prior to construction of an actual wall to prevent wasted material, time and labor. Some of the earliest recorded tests performed on masonry mortar ingredients were carried out by the U.S. Army Corps of Engineers in the construction of fortifications during the early part of the 19th century.

The durability of masonry buildings relied heavily upon the past performance of structures and the master mason’s experience with specific materials. Much of the heritage knowledge of making good mortar was passed down from generation to generation through the trades. Testing mortar ingredients historically involved the masons working with architects in a team approach for common understanding. However, signs of change began to appear as early as the 1890s. As Uriah Cummings writes in his book, “American Cements,” first published in 1898, “With their former teaching and experience on the one hand, and the testing machine on the other, the question was not long in doubt. The machine was victorious, and henceforth all judgment founded on experience was laid aside and they became blind believers in the tensile strain tests.”

What Mr. Cummings is basically referring to is the birth of the modern-day masonry testing laboratory. “The former teaching and experience on one hand” is the mason-and-architect team approach to understanding mortar that involved past failures and success at the building site. “…and the testing machine on the other” is the new way of thinking, a new approach, a move away from the old-fashioned ways, a man-made machine, ready to give the results quickly and without reservation.

Uriah Cummings (1898) American Cements (book inside cover) Portland Cement Association, Skokie, IL

Mortar
Binders in mortar have typically consisted of clay, lime putty, hydraulic lime, natural cement, hydrated lime and portland cement. The sand used to create mortar when mixed with various binders included crushed stones, seashells, river pebbles and various aggregates.

ASTM Committee C12 on Mortars for Unit Masonry was first organized in 1931 to help architects determine how to effectively choose from a list of mortar ingredients and combine their choices with the correct proportion of sand to produce the appropriate mortar mixture for a specific project requirement.

The scope of the newly formed technical committee was to prepare specifications, methods of testing, and definitions relating to mortars specifically used in masonry construction. However, the development of specifications for binders was outside the scope of Committee C12. ASTM C270 Standard Specification for Mortar for Unit Masonry was published in 1951.

Mortar recipes can be specified by volume proportion or by properties. The volume proportions are based on a ratio of one part binder to three parts aggregate. The properties required are compressive strength, water retentiveness and air content derived from air entraining admixtures. It was in this committee that the current mortar recipes and recommended mix designs and formulations of Type M; Type S; Type N; Type O; and Type K were first established in 1954. The designation mortar type letters were taken from the two words, MASON WORK, utilizing every other letter.

Railroad Depot (1910) Salida, Colorado Library of Congress

Specifying Historic Mortar Today
The challenge architects face today is that mortars, which are specified within ASTM C270, may not be compatible with historic masonry units. The compatibility test that most relates to replacement mortar formulations is it should be as similar to the original mortar as possible. At the time that the historic masonry structures were built, mortar materials such as traditional lime putty, hydraulic lime, natural cement, and the new portland cements were all products of the quarries they came from and the intentions of each manufacturer. Needless to say, there was a large degree of variance in the final product. It was the lack of agreement between the end user and the manufacturers as to what an acceptable product should look like and how it should perform that pushed the development of minimum standard specifications.

In some ways we face challenges that were similar to those of our counterparts at the turn of the 19th century. Because of the very limited scope of ASTM C270, nonstandard materials or nonstandard applications of standard materials are being specified. This leaves the architect taking design responsibility, especially when traditional masonry buildings need to be restored.

In an effort to assist the architects with this, a task group was formed in technical committee C12.03 Specifications. The new ASTM C12.03.03 Preservation Mortars Task Group was charged to develop a new standard specification for mortars for the preservation of masonry structures. The task group, made up of volunteers representing historic building owners, engineers, conservators and manufacturers, worked together to create the following mission statement:

“The C12.03.03 (Preservation Mortars) recommends that a standard be developed for mortars to be used in for the preservation of masonry, which would include clay brick, stone and terra cotta. The development of a new standard is requested because C270 does not provide a suitable specification for preservation mortars which could be bedding or pointing mortars.”

A draft standard specification is being developed. At this time, the document has not been approved by ASTM as a standard specification, but the consensus process is ongoing. It is hoped that with continued cooperation among architects, contractors and manufacturers, as well as owners of historic buildings, we can soon publish a respected new standard for traditional masonry mortars.

Equipped with an effective concept for consensus building through technical committee work that has worked for more than 100 years, it most definitively appears ASTM will continue to play a key role in our future efforts to preserve America’s historic masonry architecture.

About the Author
John Speweik is the vice president of the U.S. Heritage Group based in Chicago and has been a member of ASTM C12 and C7 committees since 1992. He assisted in the planning in the 75th anniversary celebration of Committee C12 that was held last year in Atlanta, Ga.

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