Present: Olga Bachilova, Bill Barry, Rose Marie Ballard Brak, Matthew Bronski, David Coe AIA, Michael DeLacey, Sarah DiSano, David Fixler AIA, Gus Fraser, David Gallagher, Janine Glaeser, Jack Glassman AIA, Patrick Guthrie Assoc AIA, Jean Marie Hall, Lisa Harrington, Erin Hester, Susan Hollister, Lisa Howe, Amy Cole Ives, Tom Jester, Wendall Kalsow AIA, David Kelman, Laura MacKowiak Assoc. AIA, Arthur MacLeod P.E., Melissa McGrew, Doug Manley AIA, Henry Moss AIA, Ivan Myjer, Devin Petrick, William Remsen AIA, Deborah Robinson AIA, Brian Roche, Lorraine Schnabel, Susan Schur, Judith Selwyn, Stacy Small Assoc AIA, Malcolm Smiley AIA, Robert Thomas, John Wathne, Eric Ward AIA, Sara Wermiel, Gary Wolf AIA, Jessica Zullinger 1. Forum on Mortars for Historic Masonry: Following extensive comparisons of lime-based mortars with lime/cement mortars between Historic Scotland and common practice in the United States at the Quinque Forum last summer, Ivan Myjer and Lisa Howe decided to initiate a series of new inquiries into calcium carbonate based mortars, questioning the applicability of different formulations and demystifying the discussion in general. Ivan arranged for Lorraine Schnabel from 1:1:6 Technologies Incorporated in Media, Pennsylvania to visit our committee and present the first salvo in the developing exchange about mortars for historic masonry. Lorraine and her firm generously financed her visit. As a practitioner who has been analyzing mortars for some 14 years, Lorraine offered some near-heretical assertions, namely that 1) she is not convinced that any mortar analysis method can determine precisely the exact composition of the original mortar in the building, 2) even if we could determine the exact original composition, it may not be appropriate for repair (void ration may be inappropriate for severe exposure, mortar may have failed), 3) thankfully, we don’t actually need the precise composition of the original mortar to specify an appropriate mortar, what you need are the key characteristics of the original mortar: the color and texture (determined largely by the aggregate), the void volume, and the key mechanical and physical properties -- compressive strength, vapor permeability, and absorption. Lorraine questioned the utility of most knee-jerk mortar analyses and noted that they are often done with no particular aim in mind except to show good faith in following the Preservation Brief on historic mortars, or because mortar analysis was required by the Historic Commission or SHPO. While mortar analysis does not tell us exactly what mortar to put back, analyses can sometimes be employed to help unravel the history of a building that was constructed over various generations. Sometimes, analysis can help determine the causes of mortar failure. One by one, Lorraine methodically dissected the shortcomings and imprecision of various mortar analysis methods, beginning with acid digestion, and continuing on to the less common methods (petrography, scanning electron microscopy, gravimetric analysis, and other esoterica). Starting with the most popular and common method, Lorraine emphasized that the acid digestion process gives inaccurate information on aggregate that is acid soluble. And acid digestion can be woefully inaccurate on modern Portland cement-based mortars where the cement paste cannot be completely separated from the aggregate. However, simple acid digestion methods can allow us to look at most aggregates (especially quartz) three dimensionally to assess its particle size distribution and color. This knowledge of the aggregate can be very useful both technically and visually for specifying an appropriate repair mortar. There are a number of qualitative, instrumental analyses derived from petrographic studies, such as petrography, scanning electron microscopy, and other esoterica that could eventually help us establish a base set of analyses of a suite of materials of known composition. Creating such a framework will be expensive. Well-intentioned efforts have failed before. There was an attempt in the recent past (at Nachitoches) that ended in tears. She suggested that we might visit www.rilem.org where an attempt to publish a framework for thinking about mortar analysis is underway and due out in July 2003. Look for their technical communication #169. Lorraine distributed a handy chart (see attached pdf) comparing the ingredients and steps in the making of Lime, Hydraulic Lime, Natural Cement, and Portland Cement so the similarity among their chemical make-up would be apparent (all carbonate-based materials). The same sheet showed the numbers and dates of ASTM standards for these formulations from ASTM C5 for lime in 1913 to C1489 for lime putty in 2001. (The first ASTM standard for Portland Cement was instituted in 1909.) The Getty is undertaking a “Round Robin” trial where three university labs are testing the properties of various mortars and comparing their results for consistency. Lorraine said that properties of the basic mortar types still need to be documented: mixtures of lime and cement, natural cements, lime mortar, Portland Cement, and Masonry Cement. Eventually, there should be ASTM standard compositions that are keyed to mechanical properties at a known state of cure (compressive strength, porosity, vapor permeability) as well as color and particle size distribution, texture, and void volume. Lorraine said that not enough testing has yet been done for us to truly understand the differences between lime putties and hydrated lime mortars. Also, we have not compared softer modern cement-lime mortar mixes (Type N, O) to historic mortars in any thorough systematic way. The Getty is currently sponsoring research of lime-based mortars in Central America in their usual thorough, methodical way. Some of this will be useful us, such as the effect of aged vs. non-aged lime putty. Watch for it on www.getty.edu “Cost , craft, and appropriateness determine what you put back into the wall.” Masons must be capable of using the specified materials, and specifiers should know what added value the amplified cost and trouble for unusual formulations really bring to their projects. A 60 lb. bag of dry, hydrated lime costs between $3 and $5. A bag of dry naturally hydraulic lime costs $30. A 5 gallon pail of lime putty costs $65 (and much of this is water!). Most specifiers are unclear about the mechanical properties of mortars that they define by proportion. Most are stronger than we think after 28 days of cure: Norman Weiss points out that ASTM C270 addresses “minimum” strengths. Lorraine said that we should become knowledgeable enough to guide our clients toward techniques for specifying replacement mortar that go beyond mere acid digestion analysis, but cautioned us not to overestimate the value or accuracy of any single analysis method. Lorraine stressed repeatedly that the first step in analysis is to decide what you want to know, and what you want to achieve. Many are specifying or not specifying particular kinds of lime (naturally hydraulic lime, high calcium lime, dolomitic lime) with a near religious fervor without a strong justification as to whether they are doing so for reasons of aesthetics, technical appropriateness, or purported authenticity. She noted that original lime compositions varied as widely as their regional stone sources – Chicago area limes typically were dolomitic, though today dolomitic limes are frowned upon by certain sects of lime worshippers. Lorraine beseeched us all to look at mortars less emotionally and more in terms of appropriateness for repair. Lorraine’s depth of experience, cogent presentation and refreshing candor started a lively discussion that developed in two phases. Immediately, Lisa Howe observed that the present time is comparable to the mid-19th century, when test data were lacking with new materials becoming available to displace traditional mortars and when increasingly demanding structural applications arose in rapid succession. Sara Wermiel noted that many buildings end up as patchworks with new and old mortar coexisting in the same walls and with little grasp of how the different permeabilities and strengths might interrelate or how much their differences might matter to the building’s overall performance. The committee decided to organize two more sessions in the coming year: first, a discussion about mortar specifications and their craft implications with masonry contractors who often work with old buildings; and second, to gather structural engineers together for a discussion about the mechanical properties of mortar, their behavior in walls, standards, testing, and workmanship. Next, Amy Cole Ives, Matthew Bronski and Ivan Myjer led a discussion about an hands-on mortar workshop to take advantage of June Hayward’s experience with traditional building crafts training at Historic Windsor, or perhaps connect to the masonry training workshop (Sept. 21-22, 2003) following the Association for Preservation Technology International (APTI) 2003 conference in Portland, Maine from September 17-20 next Fall. 2. Tours: a. Vermont Quarries: Matthew Bronski and Lisa Howe (APT/Northeast Chapter President) organized tours of the Danby Marble Quarry and Vermont Structural Slate quarry on October 12. Luca Mannolini, a native of Carrara Italy, and a geologist at the Vermont Quarries Corp., led the tour of the subterranean marble quarry. At the 1909 portal, a massive rectangular hole in the rocky hillside, the strata of topsoil, then dolomite (not enough heat or pressure near the surface to have metamorphosed into marble), then white Vermont marble are all visible. The road descends into a dark, cavernous Piranesian fantasy, cut from sheer white marble, touched by infrequent lights, steeped in shadow, with massive marble columns left every 60 or 70 feet to support the stone ceiling 35 ft. above. (We simply MUST have our next HRC Beaux Arts Ball here.) The various commercial types of Danby marble (Mont Clair, Imperial, Royal, etc.) are various strata in the white marble with different veining frequency and color. Occasionally, you will see an historic building of grey Vermont marble. Though technically sound, the grey marble (below the white) is not currently quarried due to lack of demand. The cutting and polishing operation is done right in the subterranean quarry, with gleaming state-of the art Italian equipment. Doug Sheldon of Vermont Structural Slate led the afternoon tour of their slate quarry in North Poultney Vermont, and their fabrication mill in Fairhaven Vermont. A weathered wood sign at the entrance reads “Eureka Quarry.” Though the old wire cable system is still in place, slate slabs are now hauled out of the pit by earthmoving equipment. We watched Doug determine the grain of the slate (secondary compression plane perpendicular to the bedding plane) then split a massive slab of slate with only a few blows on a single plug and feathers. Orientation of the grain along the long direction of the shingle (uncommon in quarries where slate is cut rather than split) is important to the typically higher flexural strength of the Vermont structural slate. Wielding her mighty hammer, Olga Bachilova split roofing slate, while Doug trimmed edges and punched nail holes. Roofing slate are still split by hand in a remarkably intact collection of vernacular wood out-buildings near the lip of the quarry that beg for documentation by HABS. To step into these buildings (including the blacksmith shop, where tongs still hang on the wall) is to step back in time. By contrast, slate countertops, floor tile, wall tile, sinks, and even gravestones are fabricated in a high-tech process in a modern facility in nearby Fairhaven, where CADD drawings are fed directly to automated machinery. Check out: www.vermontstructuralslate.com b. Frank Lloyd Wright’s Zimmerman House: Matthew Bronski and Hetty Startup, Zimmerman House Site Administrator at the Currier Gallery of Art in Manchester, New Hampshire put together an exceptionally well-managed tour of this elegant, remarkably unworn and intact (frocks and handbags in the closet) 1951 Usonian house. Matthew’s firm, Simpson, Gumpertz & Heger worked with Ann Beha Associates to reconstruct the lost red Ludowici clay tile roof, with new details for venting, ice dam prevention, and flashing. The original clay tile roof had been replaced with asphalt shingles in the late1970’s. The house is stunning, with an unexpectedly rich palette of red clay tile, brick, red concrete floors (and once, a red gravel driveway/forecourt) and beautiful cypress soffits, ceilings and walls. Two of the five Wright buildings in New England are on this quiet side street on the edge of town. The tour was well attended but for those who could not be there (jail, cleaning the attic, collecting acorns…) it is possible- even easy, to arrange or join a tour with the Currier, which owns and maintains the Zimmerman house. For tour info, go to: http://www.currier.org/browse/?gallery=zimmerman NOTE DATE CHANGE!!! (so as not to conflict with Build Boston) 8: 00 a.m., Thursday, November 21, 2002 The Architects' Building, 52 Broad Street, Boston, Fifth Floor
Henry Moss, Matthew Bronski, and Sara Wermiel Co-leaders and Scribes |