ASTM Committee C12

75 Years of Developing Mortar and Grout Standards for Masonry Construction

ASTM Committee C12 on Mortars and Grouts for Unit Masonry was organized in 1931. Therefore, this year marks the 75th anniversary of committee efforts to provide relevant, effective and practical standards on mortars and grouts for unit masonry. Milestones like this are excellent opportunities for celebration, reflection, and renewed focus on standards activities.

Celebration began this June with the dedication of the Joint ASTM Masonry Symposium to the C12 75th anniversary and will culminate this month with a special reception, banquet and program. The purpose of this article is to examine how the ASTM process, people and technology have shaped C12 standards development. The review of past activities provides context to current efforts and direction for future work.

Mortar and Grout: Materials in the Middle of Masonry Construction

The first retained record of C12 activities in 1937 defined the committee’s scope: “Committee C12 on Mortars for Unit Masonry shall prepare specifications, methods of testing and definitions relating to mortars for use with units of burned clay or shale, sand-lime, concrete and stone and similar materials used in unit masonry, other than those intended for use as refractories. Development of specifications for cementitious materials are not included in the scope of this Committee.” C12 activities have since expanded to include standards for grout for unit masonry. There are some unique aspects to this focus that have influenced standards development activities over the years.

Mortar and grout are similar but distinct materials. They are mixtures of cementitious materials, aggregates, water and perhaps admixtures, which are used by a mason in combination with masonry units to construct buildings or building elements. However, there are also significant differences between mortar and grout, best illustrated by how they are used. A mason uses mortar to place absorptive masonry units in a wall. Freshly mixed or plastic mortar must have a workable consistency such that it readily slides off of the trowel, sticks to unit bedding surfaces, and enables positioning of the unit.

In contrast, grout is poured into the cores of hollow masonry units or into grout spaces formed between wythes of masonry. Typically used in conjunction with steel reinforcement, grout must completely surround reinforcement and fill grout spaces. Therefore, grout is mixed to a highly fluid state. The grading of aggregates and proportioning with cementitious materials must be such that segregation does not occur during a grout pour.

Many of the desired characteristics of masonry as a construction system are the result of how mortars and grouts are placed in combination and interact with masonry units. That principle needs to be considered when developing standards and specifications for mortars and grouts and when developing standards for masonry units (an example is the effect of unit absorption on water requirements for freshly mixed mortar).

This general principle establishes a need for close communication and coordination between Committee C12 and Committee C15 on Manufactured Masonry Units that has existed since Committee C15’s organization in 1937. Some members of C12 and C15 have at various times advocated merging the two committees and, indeed, there have been surveys and ad hoc committees formed in the past to study that possibility. However, there are advantages to retaining separate identities and distinct areas of focus.

After the most recent discussion of potential merger in the 1990s, C12 and C15 agreed to retain separate committee status, but to formalize some activities as joint efforts. Currently, there are joint C12 and C15 subcommittees on laboratory accreditation, terminology, and symposia. Other mechanisms for improving coordination include periodically scheduling joint meetings of the executive and planning subcommittees and encouraging the many ASTM members who are active in both C12 and C15 to provide informal liaison.

Specifications for cementitious materials used in mortar and grout are developed by other ASTM committees. Within the context of Committee C12 mortar and grout standards, cementitious materials include hydraulic cements, pozzolans, hydrated lime, lime putty, and ground granulated blast furnace slag. Specifications for cement are developed by ASTM Committee C01 on Cement, and specifications for lime are developed by ASTM Committee C07 on Lime.

It has been and continues to be important to understand and consider the properties of cementitious components as specified in their material standards developed by C01 and C07 when developing C12 specifications for mortars and grouts. Thus a continuous information exchange among these committees is needed. Again, the mechanisms to accomplish this are both formal and informal. The masonry symposia previously noted as joint with C15 is actually a cooperative effort of committees C01, C07, C12, and C15. The masonry symposium held this past June was the 11th in a series that began in 1974. Since its inception Committee C12 has had active participation by individuals who were also members of C01 and/or C07, and that tradition of informal liaison continues.

The scope of committee activities encourages a diverse membership. Given the broad use of masonry as a construction system, the roles that mortar and grout play in masonry construction, and the impact component materials have on mortar and grout properties, it is not surprising that Committee C12 attracted volunteer participation by individuals from various other ASTM committees having diverse interests and backgrounds. That tradition continues, and current membership includes academia, aggregate producers, architects, block producers, brick industry, cement producers, engineers, government agencies, lime producers, mason contractors, masonry consultants, mortar and grout admixtures, new mortar materials, premixed mortars producers, testing laboratories, and others.

Literally and figuratively, mortar and grout can be viewed as occupying a position in the middle of the spectrum of masonry materials. Physically, mortar and grout are placed between units and within units. As a component of masonry construction, mortar and grout performance characteristics require consideration at various levels as follows: 1) the assembly of which they are components, 2) the mortar and grout mixture as prepared for use, and 3) the component materials from which they are mixed. Coordination and liaison is required in developing standards for mortars and grout with committees responsible for other masonry materials and assemblies and standards organizations responsible for building codes for masonry construction. The roles that mortar and grout play in masonry construction are of broad interest to a diverse group of professionals. In several respects, they are materials in the middle of masonry construction.

Development of a Specification for Mortar for Unit Masonry

The history of the development of ASTM C 270, Specification for Mortar for Unit Masonry, is particularly interesting as it identifies issues that continue to be relevant to standards activities today. Much of that work took place during the period from 1937 through 1951. Despite the disruption of World War II, this was a time of intense activity for Committee C12, and for the development of masonry-related standards by Committees C01, C07 and C15.

Committee C12, chaired by J. W. McBurney of the National Bureau of Standards (now the National Institute of Standards and Technology), published its first temporary standard in 1939, ASTM C 144-39T, Tentative Specification for Aggregate for Masonry Mortar. The first mortar specification was ASTM C 161-41T, Tentative Specification for Mortar for Reinforced Brick Masonry. ASTM C 161 contained alternate property and proportion specifications, setting the precedent for the current format of ASTM C 270, which was first published as a tentative standard in 1951. ASTM C 161 was discontinued in 1965, but ASTM C 270 and ASTM C 144 remain active standards to this day and are the primary standards on mortar and aggregates for mortar used in the United States.

An issue of particular interest in the 1930s and 1940s, and which has been a continuing topic of discussion within the committee, is the question of whether to specify mortar by performance or prescriptive criteria. Examination of past committee minutes and published ASTM proceedings dating from 1937 and the excellent summary of the ASTM C 270 development by J. Ivan Davison indicates that initial efforts to write a performance-based specification evolved into one that provided alternatives for using a modified performance-type specification and a conventional prescriptive specification. While some C12 members at the time may have been disappointed that the initial proposal to have only performance-based criteria was not accepted, the fact that the property and proportion format has served the diverse needs of the masonry industry well since its adoption is a testament to the capabilities of the people involved and the wisdom of the ASTM consensus process (see Figure 1).

Committee records also reveal some noteworthy general principles on the topic of performance and prescriptive specifications that are as applicable today as they were then. Among those principles are:

1. A goal of both a “performance specification” and “prescriptive specification” approach is to ensure that mortar as specified performs acceptably and predictably.

2. While it is generally accepted that a specification should seek to ensure desired performance, there is a significant divergence of opinion about whether that can most effectively be achieved by specifying performance properties or prescriptive criteria.

3. Challenges in developing performance standards criteria are defining required performance, developing relevant tests, and agreeing on criteria.

4. Challenges in developing prescriptive criteria are establishing that criteria ensure desired performance and providing for the qualification of new materials.

5. Whether performance-based or prescriptive, a standard specification must be practical, relevant to marketplace needs, and compatible with technological advances.

ASTM C 270-51T designated five types of mortar to be specified either by property or proportion. Initially, type designations for mortars were A-1, A-2, B, C, and D (see Tables 1 and 2), with A-1 corresponding to the highest cement content and highest compressive strength mortar. However, there was significant concern among committee members that the system of classification would tend to bias mortar selection toward higher cement content, higher strength A-1 mortar, since “A-1” had become a synonym for top quality in American culture. Then as now, it was recognized that no single mortar type or set of cementitious materials is best for all applications, and that mortar selection should be optimized to be compatible with the structural, construction, and serviceability requirements of the masonry application. In 1954 the committee revised the type designations as follows:

A-1 became M
A-2 became S
B became N
C became O
D became K

Apparently, this system of designation was developed by selecting every other letter from the phrase “mason work.” ASTM C 270 still uses this system of type designation, although Type K has been moved to an appendix on tuck-pointing mortar.

Subsequent editions of ASTM C 270 have refined the standard. Modifications include changes to clarify the distinction between the proportion and property specifications, emphasize that property specification requirements are to be determined by laboratory testing, not field testing, update materials references, and include explanatory information in an appendix. The appendix provides a primer on mortar technology and use. The information contained is a distillation of knowledge developed by the committee over the years.

Relevant, Effective and Practical Standards on Mortars and Grouts for Unit Masonry – A Continuing Theme

By 1954 Committee C12 had developed three tentative standards related to mortars for unit masonry. Today the committee has 15 active standards addressing mortar and grout topics including specifications for grout, surface bonding mortars, extended life mortars, admixtures for mortars, test methods for mortars and grouts, a terminology standard, and a guide for quality assurance for masonry mortar. Analysis of the timeline for the development of these standards (see Timeline of Key Events) and committee records reveals a continuing theme of commitment by C12 to develop standards relevant to marketplace advances in technology, effective in providing required performance, and practical for intended applications.

C12 standards development on grout materials provides a classic example of the link between evolving masonry construction technology and committee standards development. The post-war construction boom encouraged the development of new construction technologies. Advances both in design methodology and construction techniques enabled the use of grouted reinforced masonry in new building applications during the 1950s that demonstrated the robustness, versatility and efficiency of this construction system. As a result, Committee C12 initiated work to develop specifications for mortar and grout materials for reinforced masonry during this time frame. ASTM C 404-57T, Tentative Specifications for Aggregate for Masonry Grout, was published in 1957 and ASTM C 476-61T, Tentative Specification for Mortar and Grout for Reinforced Masonry, was published in 1961.

Initially, ASTM C 476 required that mortar for reinforced masonry meet both prescriptive proportion limits and property requirements. Those requirements paralleled ASTM C 270 proportion and property requirements for Type M mortar, although testing procedures for determining mortar properties were slightly modified. Grout provisions of ASTM C 476 were limited to prescriptive proportion criteria for fine and coarse grout.

During the late 1970s, the committee re-evaluated the scope, provisions, and use of C 476. This re-evaluation prompted revisions and additional development activities. Significant issues included confusion and conflict resulting from requiring mortar for reinforced masonry to meet both proportion and property criteria, misunderstanding and misuse resulting from the inclusion of provision for mortar and grout in the same standard, a lack of test criteria for grout, and the extensive modification of building codes and project specifications often made to C 476. As a result of those considerations: 1) ASTM C 476 was revised in 1980 to address grout for reinforced and nonreinforced masonry, 2) revisions to ASTM C 270 in 1982 included a change in scope to explicitly include mortar for reinforced and nonreinforced masonry, and 3) ASTM C 1019, Method for Sampling and Testing Grout was published in 1984. Subsequent revisions to ASTM C 476 incorporated a strength specification alternative to the prescriptive proportion specification criteria. These changes and activities were clearly the result of a systematic evaluation of the use of C12 standards and a commitment to improve their effectiveness and practicality.

Current Committee C12 Standards Activities and Future Work

Committee C12 continues to improve existing standards and develop new standards. A partial list of current activities includes the development of a specification for dry preblended mortar materials, a specification for restoration mortars, a performance specification for mortar not limited to ASTM C 270 materials, provisions for self-consolidating grout, re-evaluation of the distinction between mortar and grout in C12 standards, and the encouragement of research and exchange of information on mortar and grout technology.

Seventy-five years ago, a diverse group of knowledgeable individuals initiated work to develop standards for mortar for unit masonry within the ASTM voluntary consensus process. It is clear from records that Committee C12 standards development activities in following decades did not follow the direction many C12 members initially anticipated. It is equally unlikely that we can predict the specific path of future C12 standards development activities. While we might speculate that increased emphasis on economical, safe and environmentally friendly masonry construction will influence mortar and grout standards, or that advances in modeling and computer technology could lead to the development of “smart, knowledge-based” standards and the development of predictive specifications, one thing is certain. Knowledgeable and diverse volunteer participants, working within the ASTM consensus process, will continue to develop standards for mortar and grout that are relevant, effective and practical. //

John Melander is director of Product Standards and Technology for the Portland Cement Association. A recipient of the ASTM Award of Merit and ASTM Committee C01 Bryant Mather Award, he is chairman of Committee C12 on Mortars and Grouts for Unit Masonry, and a member of several ASTM technical committees, including C01 on Cement, C07 on Lime, C09 on Concrete, C12 on Mortars and Grouts, and C15 on Manufactured Masonry Units. He is president of The Masonry Society, and a member of the American Concrete Institute, and the Construction Specifications Institute.
Copyright 2006, ASTM International