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Patching Peabody's Façade

When replacement stone was unavailable for the façade restoration of the Peabody Conservatory, Quinn Evans | Architects opted for patching mortars, with fine results.

Click here for a list of masonry restoration specialists
Click here for a list of façade restoration specialists

By Hadiya Strasberg

The Peabody Conservatory of the John Hopkins University was one of the first academies of music to be established in the United States. Located in Baltimore, MD, the Italianate building was designed by Edmund Lind and constructed in two parts in 1866 and 1878. (The first part was the 600-seat Miriam A. Friedberg Concert Hall, and the George Peabody Library was the second.)

In the summer of 2001, Quinn Evans | Architects (QEA) of Washington, DC, undertook a $26.8 million renovation to integrate and revitalize the Peabody campus. The program included the enhancement of facilities and the creation of new rehearsal and performance halls, studios, practice rooms and administrative space. One of the most important aspects of the project was the cleaning and patching of select areas of the conservatory's white marble façade.

The condition of the building before restoration was poor. The north façade was covered with layers of urban dirt and deep staining caused by water, minerals and paint. The columns, especially the column bases, were in similar condition to the façade, and surface spalling associated from freeze-thaw cycling and de-icing salts was found around the stairs. Because surface erosion was also an issue, it was not possible to determine the original finish. A cast-iron canopy, a 1917 addition to the entrance to Friedberg Concert Hall, was in very poor condition and was removed as part of the renovation project. This left iron stains, holes and damage resulting from the removal process.

Fortunately, QEA was able to review the original documentation of the building, including drawings, construction correspondence and annual reports. “This helped immensely,” says Baird M. Smith, AIA, FAPT, of QEA. “We were able to identify that the marble came from local Maryland quarries [i.e., Beaver Dam, Cockeysville and Texas – about 75 miles from the building].” However, these quarries had gone out of business in the middle of the 20th century. “We attempted to find a match at the remaining three or four quarries nearby and from other sources in Georgia and Vermont, but the differences in the marble were too great,” says Smith.

“The next route we took," he adds, "was recovering some stone from a hidden location on the side of the building.” Smith points out, however, that the stone was unusable, because it was not a good match. QEA concluded that Dutchman repairs wouldn’t work because the only obtainable stone had gray veins and other dark striations and a horizontal pattern that did not match the original marble. “The original stone was a pure white, with light gray veining,” says Smith. “When considering patches, one must look closely because the marble is often unique for color, veins and color striations.”

Given that the original marble was unobtainable and that shaping and carving replacement stone were difficult, QEA chose to use a patching compound. “We went with Cathedral Stone Products,” Smith says, “because our contractor had worked with the company’s mortars before and gotten good results.” The Hanover, MD-based company manufactures custom patching mortars for all types of stone. It offers products designed to last at least 50 years, with a long warranty. The mortars don’t contain bonding agents, latex or acrylic latex and so are water and salt breathable. Also, the mortars can be custom tweaked to address specific problems cracking due to excess salt content, cracking, for example.

In order to purchase mortars from Cathedral Stone, one must attend a three-day, hands-on training program taught by masons. “The application of our mortars requires traditional masonry skills,” explains Cathedral Stone's president, Dennis Rude. “The workers on-site need to be able to recognize specific issues that may arise on their particular project with this particular material.” Laura Oliphant, an historic restoration specialist certified by Cathedral Stone, was sub-contracted to make the Jahn mortar on-site and oversee its application.

Oliphant customized Cathedral Stone’s base mortar for marble, Jahn M120, a cementitious, mineral-based mortar. She prepared seven test samples and a dry mix that attempted to match the appearance of the white marble. As with all samples, each one took three to six days to formulate and was assigned a unique number; all samples are retained for one year. However, “not one of these first patches was a good match,” Smith says, “because the color was off each time.” QEA had three final samples prepared, all of which were very good color matches and had good shapes and contours.

In preparation of the application of the Jahn mortar, the site was cleaned of all dirt, dust and foreign substrates to ensure proper adhesion. The masonry contractor, Todd Anderson of Baltimore, MD-based Worcester Eisenbrandt used the mortar for all patches, ranging from ¼ in. deep by 2 or 3 ins. to as large as 24 ins. across the face by 2 to 6 ins. deep by nearly 6 ft. long.

The dry patching material was mixed with water [approximately 4½ parts powder to 1 part water by volume] until the mixture was easy to spread. “You need to work through this process slowly,” Anderson explains,” because the water affects not only the consistency but also the color if you add too much.” Worcester Eisenbrandt was working in the late fall and early winter so the mix remained workable for four to six hours, long enough to make long or deep patches. “We repaired the majority of the holes in cool weather, but it never got below freezing,” says Anderson. “It could have an impact on the mortar and its adhesion, but in the unlikely event it will, not a large one.”

The area that needed the greatest attention was the entry where the cast-iron canopy had been removed. “It was very important, because it’s at the front door,” explains Smith. “We wanted this patch to be as invisible as possible.” The stone in this area had very little graining and was very white, except for the streaks of iron and water stains. After the Jahn patch had been placed, it was then “tinted” by the artisan. The entire façade could not be cleaned due to budgetary restrictions, but the stone around the entry was given priority and cleaned as well as possible.

To obtain the texture that had resulted from many years of weathering, ground marble dust was sprinkled onto the placed mortar patches. “This imparted texture and light reflectance,” Smith says. Another practice in matching the patches to the weathered and, in some cases, still-stained stone is to paint tints onto the Jahn. “Sound preservation philosophy indicates that patches should match the color and texture of the original stone and not of the weathered stone,” Smith says. “But since the entire façade could not be cleaned, we ultimately decided to match the repairs to the staining left on the adjacent stones.” Silin-brand silicon-based masonry paint was used to blend the new work so the appearance could be as seamless as possible.

Shortly afterward, QEA finished work on the marble façade, creating a cohesive façade that is cleaner and uniform in color, veining, staining and texture. “Everyone is extremely pleased with the stone repairs and cleaning,” says Smith. “In fact, most people cannot identify the patches. They remain nearly invisible.”

Click here for a list of masonry restoration specialists
Click here for a list of façade restoration specialists