Around 1846 lime began to gain popularity over erosion-prone mud; It was popular for plasters and for mortar in much construction until the arrival of Portland cement during the first decade of the 20th century.
This first instance of the term “cement stucco” in the archives of the Santa Fe New Mexican appeared in 1907, but in the second half of the 19th century, lime was king.
Making lime involves a series of steps. First you burn chunks of limestone in a hot kiln. The resulting quicklime is very caustic and potentially explosive with moisture. “In old engravings of masons, you’ll see guys wearing eye patches,” contractor Alan Watson said, “because if a piece of that quicklime hits the moisture in your eye, bang! it just burns your eyeball out.”
The second major step in the process was to “slake” the quicklime in water to produce lime mortars and plasters. “It’s a fairly sophisticated process,” Watson said. “It’s useful because it’s a material that is a solid that can be turned into a plastic material and then returned to a solid state.”
The technology can be traced back at least to Neolithic times at the end of the Stone Age. In the 1980s, more than a dozen human statues — some of them two-headed — were discovered in Jordan. The lime-plaster figures survive from the 9,000-year-old farming settlement of ’Ain Ghazal.
Watson said that all the Mayan sites in Mexico were done with lime plasters and mortars. “The Spanish knew about it when they arrived in New Mexico, but it was already in place in Mexico. As far as I know, it never got further north than Ciudad Juarez until the Americans showed up. The first evidence that I know of is out at Fort Union, which was established in the 1850s. There are two kilns over there.”
Although masons today use small amounts of a relatively inferior product called hydrated lime in their cement mixes to add plasticity, lime in its pure form is not routinely used for mortar and plaster on buildings, except in preservation work. Contractors like Mac Watson and Edward Crocker who have done a great deal of work on historic buildings in Santa Fe do employ lime in repair work. They’re also fascinated with locating historic lime kilns and slaking pits.
In 2011, a three-century-old slaking pit was discovered next to the cathedral during city-required archaeological testing. “I concluded that the lime slaking pit dated to 1717, and was probably used during construction of the second parroquia [parish church] in that year,” said James L. Moore, Museum of New Mexico Office of Archaeological Studies.
Crocker said that the longer lime “has been run into a putty and kept moist, the more plastic and well-behaved it is.” The quality of lime increases the longer it slakes, and there are accounts of master craftsmen who would only use material that slaked for decades.
Craftsmen dug slaking pits near the buildings on which the lime would be used. On the other hand, lime kilns were built at sources of limestone. Sometimes, kilns were far from the slaking pits.
Watson said, “Part of the design of the kiln is to get something that drafts like crazy because you’re trying to create a pretty intense fire, so you keep feeding it.”
Scouting out good limestone sources was key to lime technology. One glimpse into Santa Fe’s history comes from a moment during a 1964 interview with the sculptor Eugenie Shonnard who spoke about finding limestone and clay on Cerro Gordo.
Lime plaster bonds well with stone — the rougher the better — but what about using lime plaster on an adobe building? In one of his “Understanding Adobe” columns Crocker wrote that lime and adobe are only moderately compatible and that old-timers employed a rajuelar technique that is no longer affordable because of the labor involved. “The term rajuelar is a Spanish verb connoting the application of stone, or rajuela,” Crocker wrote. “The application in this case is of small, spatulate, preferably angular and permeable pieces of rock in the mortar joints between the adobes. With the rajuelas protruding, say, three-quarters of an inch beyond the vertical plane of the wall, an effective lath was created. The embedded stones supported the lime plaster.”
Another aid to the adherence of lime to adobe is the wetting of the adobe immediately before application, Watson added. This was the method employed at the historic church in Cañoncito. “We did the lime plastering on Our Lady of Light when I was working for Cornerstones in the mid-1990s,” he said. “It’s one of the few structures in Northern New Mexico that I know of that has been coated on the outside with lime plaster, and it’s held up pretty well.”
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