Present: Bill Barry, Matthew Bronski, Michael DeLacey, Marc Demaree, Sarah Gray, Patrick Guthrie, Lisa Howe, Susan Hollister, Susan Hurst, Amy Cole-Ives, Wendall Kalsow, David Kelman, Michael F. Lynch, Laura Mackowiak, Jackie McBride, Doug Manley, Henry Moss, Ivan Myjer, Bettina Norton, John Ochsendorf, Albert Rex, Brian Roche, Stacy Small, Susan Schur, Malcolm Smiley, Kim Sykes, Malcolm Smiley, Jonathan Smith, Robert Thomas, Hamid Vossoughi, Mark Webster, Sara Wermiel 1. Gaiety Theater (Publix Cinema), Washington Street: Henry Moss reported that the Boston Landmarks Commission had voted 5-3 in favor of further study of a proposal to upgrade the level of listing of the Gaiety and designate the building a local landmark. Henry had visited the theater and written as a chair of the BSA Historic Resources Committee against the proposed increased protection, because of the loss of original features and because of obstacles to its economic reuse as a theater (size, loading access, depth of stage). Michael DeLacey expressed his disappointment that the BSA had not supported the grassroots movement dedicated to protection and reuse of the Gaiety. Michael Lynch responded that a representative of the Society of Architectural Historians visited the building and also reached the conclusion that the Gaiety's designation should not be altered. Michael DeLacey made the general point that a growing interdependence of economic interests among developers and the "institutionalized" voices of the historic preservation movement now make it more difficult than ever for grassroots activists to succeed in their causes. This point should not be ignored, regardless of how we feel about the Gaiety case. Past examples where historic buildings have prevailed, despite financial imperatives that appeared to sweep away preservation arguments, include the Coolidge Corner Cinema, the Vilna Shul, the Keith Memorial Theater, and Fenway Park. However, in each of these instances, there was more agreement about the integrity of the original building fabric than with the Gaiety Theater. The preservation movement benefits from having advocates who are passionately committed to the curatorial value of specific historic sites and buildings. It is also important that we maintain a group of commentators less tied to individual causes and with more responsibility to evaluate the relative significance and integrity of many different buildings, and consider a broader mix of economic and social variables. The friction between these roles may be uncomfortable, but it results from valuable differences in points-of-view. 2. Mortars for Historic Buildings, the Engineers' Perspective: As the first follow-up to Lorraine Schnabel's outstanding and contrarian presentation on mortar analysis and specification, Part Two in our ongoing Mortar series presented engineers' views on the structural considerations of mortar and historic masonry. The evening panel discussion, held at the offices of Shepley, Bulfinch, Richardson and Abbott, was organized by Ivan Myjer and Matthew Bronski. Panelists included three structural engineers (John Wathne of Structures North, Brent Gabby of Simpson, Gumpertz & Heger, and John Ochsendorf of MIT), and one Mechanical Engineer/Architect/Steward Extraordinaire (Michael Lynch of SPNEA). Michael Lynch noted that SPNEA has little experience with structural repair of masonry, since all but one of their historic houses are wood-frame construction. Their typical masonry repairs involve repointing foundation walls, and for this relatively straightforward repair with little structural implication, repointing with slaked lime mortar works reasonably well. Michael mentioned that most of the chimneys of SPNEA's historic houses were completely rebuilt in the 1950's or 70's using modern brick with whatever cement-lime mortar the National Park Service recommended at that particular time (roughly Type O?). Oddly, while most of the chimneys on nondescript capes and ranches built in the 50's and 70's using modern brick and hard modern mortars are in fine condition, many of the SPNEA chimneys rebuilt using modern brick with soft mortar and Park Services specs are now in poor condition, with separations between the mortar and brick, to the point where Michael said some individual bricks can be pulled-out by hand and portions of some chimneys could probably be pushed over (a perplexing situation). John Wathne and Brent Gabby each described similar case studies of mortar selection for rebuilding the outer wythe of granite (reusing the original stones) in deteriorated 19th century church towers. John Wathne described repairs to Immaculate Conception Church in Lowell, an 1870's building with a single stone tower. The tower walls were 30" thick, with an outer wythe of granite ashlar and a core of stone rubble. The outer 8-10 inches of mortar was severely deteriorated due to freeze/thaw damage and needed to be rebuilt, while most of the rubble back-up was essentially sound. John observed that the rubble stone core was mostly mortar, with no stone-to-stone contact, suggesting that the original mortar had a very quick set time to prevent the stones from settling into contact. Analysis by Lorraine Schnabel confirmed naturally hydraulic properties (and consequently quick set time) of the original mortar. Because the ratio of granite to mortar was much higher on the exterior ashlar than in the wall's core (which was mostly mortar), the outer wythe had a lower permeability than the core of the wall, even as originally built using all lime mortar. John was reluctant to exacerbate this existing condition by using a low permeability mortar to rebuild the outer wythe. In searching for a replacement mortar, John looked for a high permeability mortar with a reasonably quick set time, good durability, and reasonably good compressive strength. He considered Types N and O cement-lime mortars (good strength, inexpensive, fast set time, but relatively low permeability), lime putty (high permeability, but little compressive strength, extremely long set time, and extremely expensive) and naturally hydraulic lime mix (moderate compressive strength, high permeability, reasonable set time, expensive). He chose a naturally hydraulic lime mix, using a Riverton Lime from Virginia. The repairs were successfully completed a few years ago, and prisms of the new mortar were archived at the church for future strength testing (as lime mortar continues to gain strength slowly over time). John emphasized that he does NOT think naturally hydraulic lime is the perfect material for all historic projects, though some seem to think so. But he considered it the best choice for the particular circumstances of the Lowell project. Brent Gabby described mock-up testing for repairs to the twin towers of a granite fieldstone chapel in Brunswick, Maine, designed by Richard Upjohn in 1847. The outer 8-12" of the lime mortar, including the collar joint, basically had reverted to sand. Consequently, the outer wythe of granite was sloughing-off the towers. Petrographic analysis of the original mortar indicated naturally hydraulic properties to the lime. Trial repair attempts to re-bond the outer wythe to the core in-situ, using grout-injection techniques, were not effective. Consequently, Brent is now designing repairs to remove and reinstall the existing outer wythe of granite and conducting trials of candidate mortars in the SGH laboratory. For this project, Brent is primarily looking for bond and durability in the new mortar. Because stresses in the tower are low, he is not concerned with compressive strength of the new mortar. He also is unconcerned with permeability of the mortar, for two reasons: 1) the towers are not heated or air conditioned, and hence have no significant vapor drive, and 2) because the granite has such a low permeability, even a pure cement grout would have a greater permeability than the stone. To test how various mortars would bond to the granite, SGH built 4 trial walls, each 3' x 3' x 1' thick. Three walls used naturally hydraulic limes (Riverton from USA, St. Astier from France, and Blue Lias from England), and one used portland cement grout as a control. The Blue Lias didn't bond at all, the Riverton and St. Astier limes appeared to bond, and the portland cement bonded extremely well. Direct tensile testing confirmed good bond of the portland cement to the granite, but bond on the Riverton and St. Astier samples was too weak even to survive sample prep. Prior to constructing and testing sample panels, Brent expected that at least one of the hydraulic limes would prove suitable. Testing and design are still in progress but the surprising results are pointing toward use of a portland cement grout, possibly with microsilica additives to consume free calcium and limit efflorescence. Phase I of the repairs are expected to commence in 2003. John Ochsendorf mentioned that his primary interest and knowledge is not in the chemical makeup of mortars, but in overall analysis of the stability of unreinforced historic masonry structures. John stated that too often, engineers analyze historic unreinforced masonry structures to determine how much load they can take before failure. But seldom does one need to know how much load we can pile on top of a dome or arch before it fails: rather, we are interested in how much displacement (bowing, leaning, movement of individual stones) can occur under the existing loads before collapse occurs. Minor cracking and movements occur in unreinforced masonry structures over time, and aren't necessarily cause for concern, as for example, cracks allow an arch to adjust to spreading or settlement of foundations, as the cracks form "hinges" in the arch and a new point of static equilibrium is reached. However, just because a structure has stood for a long time doesn't necessarily mean it is stable; displacements can progressively worsen with no new point of equilibrium reached. John cited the campanille in Venice as a prominent example of the latter. It stood for over a hundred years, but when displacements reached "the point of no return," the locals knew it would collapse within days and couldn't do a thing about it (other than to set up a lot of cameras and thoroughly document the collapse). Mortar Forum Part 3: What Happens in the Field? Wendall Kalsow is helping Ivan organize the next session, which will explore mortar from the perspectives of masonry contractors and their field operatives. It will be held in early 2003. Do you know how contractors quantify the components of the mortar mixes you specify? How much do we know about aggregates beyond their effect on the visual attributes of pointing mortar? Do we know how to relate our mortar formulations to the limes, cements, and aggregates available to local suppliers? Stay tuned for a date and time! 3. Façade Inspection Ordinances: The BSA Building Envelope Committee asked whether our committee might create a combined recommendation to Boston's Inspectional Services Department about improving their existing Façade Inspection Ordinance. This new interest was stimulated, at least in part, by the fall of a large stone modillion from 10 Post Office Square. Matthew Bronski noted that currently, Boston buildings 75' or taller must be inspected every four years, but that only buildings 125' or taller are required to have a "hands-on" inspection. Chicago is much more stringent for buildings constructed prior to 1950, requiring thorough "hands-on" inspections with at least 3 exploratory openings on each façade elevation to examine concealed wall conditions (e.g., corroded embedded steel framing). In 2003, ASTM expects to publish a guideline that will recommend a minimum number of "drops" for close-up inspection, and the types of construction and facade materials that require exploratory openings. ISD is aware of this ASTM effort and appears to want to evaluate the document before launching a reexamination of the existing Boston ordinance. Ivan Myjer and others recalled the preemptive removals of masonry cornices by building owners in New York City when their first ordinance, Local Law 10, was passed in 1980. Some wondered whether a stricter ordinance in Boston might prompt similar unnecessary removals of cornices, while others wondered whether thorough inspections and reports filed with the City might prompt owners to undertake long-neglected and much-needed maintenance and repairs. More on this as we discuss it further. 4. Historic Masonry Arches and Vaults: John Ochsendorf, Assistant Professor of Building Technology at MIT's Department of Architecture, followed these increasingly alarming exchanges about masonry failures with a provocative proposal for engineers to rethink their common methods for evaluating the stability of unreinforced masonry structures. From the outset, it was clear that John loves these structures, perhaps because their forms necessarily relate closely to their internal forces (unreinforced masonry structures must have a logical form, while reinforced concrete structures can easily "lie"), and because of the sustainability inherent in their material selections and ingenuity required to build long span masonry vaults and arches. John's engineering research is informed by an interest in construction history, when fine architecture and lasting, buildable solutions arose before numerical theory existed to predict their performance. Jacques Heyman was John's mentor at Cambridge University, where he did his doctorate, and we might also search out his books, among them, The Stone Skeleton, Cambridge University Press, 1966/97. Unreinforced masonry structures typically depend upon geometrically balanced masses and forces for stability. Masonry walls are not perfectly uniform or homogenous, consequently their material properties cannot be precisely known. For analysis of the stability of unreinforced masonry structures, John advocated a "back to the future" approach of limit analysis (graphic analysis using thrust lines), rather than the more common post-Coloumb numerical analysis based on methods of elasticity and precise quantification of material properties and strengths. Elastic analysis techniques (numerical) developed after Coulomb's theories (1773) departed from the more intuitive proportioning and thrust-line methods (graphic analysis) of understanding arch and buttress stability. Robert Hooke, best known to modern engineers for his contributions to elasticity theory (Hooke's Law: Modulus of Elasticity = Stress/strain) also authored the far more intuitive and catchy turn-of-phrase "As hangs the flexible line, so but inverted stands the rigid arch." Flexible lines (ropes and cables) can only take tension. Quite simply, Hooke realized the shape described by a hanging rope is in pure tension: flip that shape upside-down, and you have a form that is in pure compression (the perfect form for a masonry arch which can only take compression). John showed the more complex example of a pointed Gothic arch: a rope will hang in that inverted configuration only with a point load at the apex: consequently, a pointed arch is only stable with a point load at its apex. No stranger to pointed arches surmounted with point loads, John's research includes studies of the Cathedral of Palma de Mallorca, in an earthquake-prone region of Spain, where the most slender piers in Gothic construction rise upwards 44 meters and support a 40 ton pile of loose masonry blocks stacked at the apex of the pointed arches (concealed from view by the vaulted ceiling). A similarly top-loaded Gothic structure (Basilica of St. Francis of Assisi) collapsed during an earthquake in 1997, prompting concerns over the top-heavy loads at Mallorca. Rubio's graphic analysis with thrust lines found that the Cathedral is stable but precarious (little margin for further displacement). A photoelastic modeling analysis by Prof. Robert Mark concluded that the Cathedral is unstable. John is using long-term monitoring of displacement measurements in association with limit analysis to determine whether some of the massive loads in the attic piled on the pointed arches may be lightened, and whether removable ties could be usefully introduced to reduce the likelihood of structural damage in an earthquake. (John noted in passing that the collapse of several tall, slender Gothic structures in seismic regions of Spain in the 1700's prompted the squat, earth-hugging style colloquially known as "Earthquake Baroque"). Melding his parallel interests in sustainable design and historic structures, John made a provocative comparison between the Inca (grass) suspension bridge (extraordinarily light pure tension structure) and the stone arches of Gothic construction (extraordinarily heavy pure compression structure). The Inca bridge has high stresses, high maintenance, low first cost, short life (ritually rebuilt as part of a festival every three years), made from renewable, inexpensive, readily available unprocessed local material (grass on the adjacent hillside). The Palma arches are low stress, low maintenance, long life, high first cost, with reusable materials (large stone blocks), and high load capacity. Both are sustainable structures that beautifully express their forms as a direct result of their materials and internal stresses. John expressed his pleasure at finding an enthusiastic community interested in the details and construction of historic buildings. He hopes to bring an exhibition on Guastavino tile construction to Boston. Norman Weiss suggested that it should really go to New York, which elicited boos from our normally polite crowd. (How often must we remind our friends in NYC that the Guastavino factory was in Woburn, MA?) 8: 00 a.m., Thursday, January 9, 2003 The Architects' Building, 52 Broad Street - Fifth Floor, Boston, Mass. |