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Present: Thomas Berenetes, Michael Blutt, Susan Brauner, Steve Brown, Rebecca Bunrock, Tom Burgess, Cynthia Deschenes, David Gallagher, Jack Glassman, David M. Hart, Olga Hathaway, David Kelman, Mark Landry, Ellen Lipsey, Henry Moss, Jay Murray, Ryan Maciej, Ivan Myjer, Deane Rykerson, Amanda Sanders, Susan Schur, Malcolm Smiley, Bill Somerfeld, Drew Sondles, Marie Sorensen, Lynne Spencer, David Torrey, Natalie Wampler, Eric Ward, John Wathne, Sara Wermiel, Tim Withers, Gary Wolf, Herb Zeller 1. APT NE Building Insulation Conference: Henry Moss reported that about a dozen architects, preservation non-profit staff, conservators, masonry specialists, contractors, and engineers from the Boston area attended the APT Northeast Chapter symposium in New York City, which dealt with energy efficiency, insulation, and historic building envelopes. Attendees felt that overall the content was very good. It was well attended by people to whom these issues matter (about 200).
2. ASTM C1713-10, Standard Specification of Mortars for the Repair of Historic Masonry: This is a new ASTM standard that "covers mortar for the repair of masonry that was constructed with methods and materials that pre-date the origination of current standards of construction that are compatible with it." John Wathne, President of Structures North, has been involved for seven years with the task group that worked on this specification and chaired the effort for the past three years. [John may not acknowledge the magnitude of his contribution in terms of lost work days and travel expenses.] Unanimous agreement was required among the 140 people who eligible to vote for the standard to be adopted. John alluded to the complexity of reaching consensus among the many manufacturers and contractors interested in this specification. Although the pre-1900 building stock represents a small part of the cement industry's income, their voice was often loudest among members of the task group. John was the only design professional on the group. ASTM C1713-10 is now formally instituted (you buy a copy at http://www.astm.org/Standards/C1713.htm). At next year's APT conference in Denver, Margaret Thompson and Mike Schuyler will make a presentation about it. John remains interested in how people decide to apply the standard as specifiers and how it is interpreted in the field. Lynne Spencer said that Menders, Torrey & Spencer is the first firm to use ASTM C1713-10 in our area (perhaps anywhere in the United States), at Bulfinch's First Church in Lancaster, Massachusetts. John walked the committee through the text of the C1713. He began with the discomfiting image of eroded mortar in the famously deteriorated brickwork of Pine Bank, which once stood at Jamaica Pond. The mortar had lost its binding strength after only 100 years of normal use, fire, collapse, purposeful neglect, and general desuetude. The new ASTM focuses on the chemical and mechanical compatibilities among the binders, aggregates, and unit masonry materials. Most of the commonly used binders (clay, lime putty, hydraulic lime, natural cement, Portland cement) have ASTM standards to use for quality control. ASTM C270 addresses mortars for new construction. (John said the task group found it difficult to decide if "binder" or "cementitious material" was the better term to use. The term binder is not used by the cement industry; but our committee seemed comfortable with both.) Tim Withers raised the question of how lab tests to establish compliance with standards realistically relate to field installations, where test results may not reflect the actual performance of masonry in the actual wall. John acknowledged the possibility of variations in breaking strength results and noted that adequate curing time is critical prior to testing. The compressive strength of mortar in masonry walls improves asymptotically throughout the life of the wall. John's view is that Water Vapor Permeability (WVP) is the most important of several key properties as it limits maximum compressive strength. Water retention is another important characteristic of binders as it can affect hydration and cementation if the suction of masonry units is very high. ASTM C1713-10 identifies three groups of binders: L Carbonating, lime-based HL Hydrated lime HC Hydraulic cement ASTM C1713-10 offers two different approaches to mortar specification: Proportion or Properties. The latter is likely to be more suitable to large projects with custom pre-mixes delivered to the site. An important financial consideration is linked to the relationship of silica content to the length of time required to reach 75% of specified compressive strength. Portland cement reaches higher compressive strengths faster than natural cement, which is faster than lime-based mortar that is, in turn, faster than lime mortar. This property governs how rapidly walls can be raised. John emphasized that the information about curing time and strengths for different formulations is in the public domain. ASTM C1713-10 is the first standard to address WVP. As silica content is reduced, water vapor permeability increases. This property is not the same as porosity and it is usually more important to the performance of a wall. Terms have changed, too. Mortars for historic masonry will no longer be designated as Type M, S, N, O and K. [Thank Heaven.] Mortars will be identified according to their constituent elements. Ivan Myjer and Tim Withers raised the point of variations between field conditions and lab tests for water content in mortar. Ivan reminded us to be careful not to always default to lowest strength, highest permeability mixes, because they can increase the migration of salts. [See Matthew Bronski's week 13 letter from Rome on situations where harder and softer mortars in ancient walls have not always obeyed our rules of thumb. A link to Matthew's blog and other useful websites can be found at the HRC website links page. John addressed Part 7 of the new standard, Test Samples and their preparation, and again pointed to the difference between specifying by proportion and specifying by property. The standard sets up a series of seven materials in the cement/lime/sand sequence. John also recognized the frequent difference in sand attributes between applications for concealed and exposed mortar joints. Next steps- John and his colleagues from the ASTM task group hope to receive comments that can lead to revisions that improve the standard. He plans to add an appendix with commentary that will help people use the standard more easily, and an annex that would contain public domain test values and target values for mortar mixes with different purposes. For more on mortars, Matthew Bronski recommends Lorraine Schnabel's excellent presentation to HRC some years ago. He writes, "Her comments and insights are still as relevant today as they were then, 8 years ago." 3. East Boston Immigration Building: Susan Brauner announced that Massport seeks to redevelop the site where this building is located. Congressman Capuano's office has supported the local preservation community's request for an architectural and engineering study of the existing building. The Boston Landmarks Commission is prepared to act upon an earlier petition for local landmark status by authorizing a study report. Susan's advocacy for the building has also received support from the Boston Preservation Alliance.
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