Plaster and the California Missions

by Catherine Howlett | January 5, 2013 4:39 pm

Photo courtesy Merlex[1]
Photo courtesy Merlex

by Nick Brown, CEPE
As the most viewable buildings of their era still standing, the California Missions are not only state history made corporeal, but also one of the major reasons stucco is so common in the Southwest.

These 21 sites are rooted in Spanish, Moorish, and Mexican traditions, but many argue they represent a unique architectural style all their own. Plaster products were widely used in the Missions, and provide the stucco industry with its most relevant historical reference point. From the first Mission in San Diego in 1769 to the final one begun in 1823 north of San Francisco, the network of Spanish Missions did more to create the stucco industry than any other factor.

The Missions all started humbly, as these were frontier outposts. They worked with what was available—adobe, ladrillo bricks, and stone:

The first temporary quarters, hastily built, were little better than brush huts with grass-thatched roofs… The second structure at most of the missions was of adobe… As soon, however, as a mission was strong and prosperous, the pride of the padre usually extended to an ambition to build a church in more lasting material, hence stone or burned brick were employed. (E. Engenhoff, Fabricas [Sacramento: California Division of Natural Resources, Division of Mines, 1952], 181, as observed by Eugene Duflot de Mofras during his visit in 1840-42.)

As through the course of human history, once the Missions became prosperous, they were plastered. These churches had exterior plaster of lime-and-sand stucco, following the Roman formula of three parts clean, washed sand to one part burned lime, slaked with water. (See E. Kimbro and J. Costello’s book, The California Missions, published in 2009 by the Getty Conservation Institute.) Incredibly, the Mission construction projects drew from Roman records of building techniques written 17 centuries earlier, notably Vitruvius’s De architectura, as evidenced by books found in several Mission libraries.

Mission walls and ceilings
Together with clay roof tiles, the plaster served a vital function—protecting the underlying adobe blocks, ladrillo bricks, and stone units in the walls from moisture. When roofed, plastered, and protected from groundwater, the durable adobe walls provided effective insulation, but their soft surfaces did not lend themselves to decorative relief. A lime-based whitewash served as the final wall surface, additional protection from the weather, and an attractive finish.

California’s Mission San Luis Rey de Francia, founded in the late 18th century, relied on a compound comprising adobe blocks with lime wash, along with structures of adobe and kiln-fired ladrillo bricks and stone. Photograph © Geographer, Wikipedia. Photo licensed under Creative Commons Attribution-1.0. Generic[2]
California’s Mission San Luis Rey de Francia, founded in the late 18th century, relied on a compound comprising adobe blocks with lime wash, along with structures of adobe and kiln-fired ladrillo bricks and stone.
Photograph © Geographer, Wikipedia. Photo licensed under Creative Commons Attribution-1.0. Generic

Mission compounds were mixes of adobe blocks with lime wash, structures of adobe and kiln-fired ladrillo bricks, and stone. The Mission’s prosperity at the time of construction determined the materials, along with the function of the building. For example, important structures like the church and convent tended to have a final plaster made of lime, which produced a hard and durable finish.

Ladrillos provided improved weather resistance and sharper lines not possible with adobe; they were widely used at Missions San Luis Rey (Oceanside), San Antonio (Monterey County), and San Diego. Prominent stone churches were built at Mission Santa Barbara, San Gabriel, and the now-ruined San Juan Capistrano. Nothing made a padre prouder than building a stone church clad in white plaster.

Interior wall decoration
While exterior walls were left simple and bare, interior walls were extensively decorated. Where Mission jobsites could not use expensive wood and stone features, they often painted them on the walls. ‘Dado’ wainscots were common, as were painted cornices at the tops of the walls. Traditional fresco painting was rare in Alta California, identified only recently at the Royal Presidio Chapel in Monterey. Executed on wet plaster, this technique allowed the paint to bond with the wall, resulting in a more durable finish.

Many of the colorful decorations used on Mission interiors were later covered due to a desire to dissociate with the buildings’ Catholic and Hispanic heritages. Some of the buildings were redecorated according to British Victorian taste, both literally and figuratively ‘whitewashed.’ Many other painted decorations were covered in wood paneling, or damaged by years of neglect. (Many of these decorations only survive today because of a New Deal-era survey of American art called the Index of American Design. Now housed at the National Gallery of Art in Washington, D.C., it contains the full spectrum of American art up to the 1930s, and included many California Mission wall decorations that would not have otherwise survived. Visit[3] and select “Folk Arts of the Spanish Southwest.” Mission San Miguel, near Paso Robles, is the only surviving completely original interior.)

 Restoration specialist Thom Susko came across problems with portland cement repairs on a job. He restored the building using lime plaster and lime paint. Photos courtesy Merlex[4]

Restoration specialist Thom Susko came across problems with portland cement repairs on a job. He restored the building using lime plaster and lime paint.
Photos courtesy Merlex

The Hispanic builders and Native American workers were both experienced with paint materials:

Red was made from hematite (red ochre) and cinnabar, white from diatomaceous earth (chalklike fossil rock), and black from charcoal, burned graphite, and asphaltum. To these sources, the Spanish added pigments imported from Mexico… and linseed oil, used as a binder. (See E. Kimbro and J. Costello’s book, The California Missions, published in 2009 by the Getty Conservation Institute.)

One Chumash artist was said to have employed “meat of the red tuna, egg whites, and pitch to the pigments. He also used urine, which he collected in clay pots, as a mordant for the paint.” (See E. Kimbro and J. Costello’s book, The California Missions, published in 2009 by the Getty Conservation Institute.) Sometimes the old way is the best, as with lime plasters; other times, when the old way involves bodily-fluid paint, it is perhaps best left buried.

Restoration of California Missions
As the Missions faded from public interest, they were neglected. The fairly simple maintenance required to preserve adobe and stone buildings was not done; in extreme cases, walls dissolved back into the mud from which they were made. Earthquakes accelerated the deterioration of many buildings.

Concerned citizen groups organized to save and restore the Missions—thankfully, many are now maintained and well-financed. The restoration work has shown what works with these walls and what does not. Bluntly put, portland cement repairs do not work in these instances.

Well-intentioned repair efforts used portland cement in the 1940s, 1950s, and 1960s on walls that had lasted almost two centuries. Portland cement was not only inexpensive and readily available, but it was also stronger than the original materials. Therefore, it was reasonable to believe cement repair products would only strengthen the structures. Unfortunately, when applied to adobe walls (and often over chicken wire), the material’s hard, water-repellent surface proved so impermeable that when moisture did occur in the walls, it remained trapped behind the cement veneer, slowly eroding the adobe wall from within.

In other cases, a cement mortar was added to ladrillo constructions, and over time, it pulled away the surface of the tiles. The original lime mortars and plasters were porous and had allowed modest dampness to evaporate. Traditional lime- or earth-based renders (exterior plaster) and finishes protected adobe bricks from direct contact with the weather, providing an easily replaceable ‘sacrificial layer.’

Current restoration methods
Today, mission repairs use renders and mortars similar to the original material, allowing the walls to breathe. Consequently, Mission ladrillo arcades are re-mortared and re-stuccoed using soft lime mortars—a product that is also durable and easily maintained. Additionally, the hard feel of cured limestone hides an inner softness that gently coats and supports masonry units without breaking them (as in the case of various portland cement products).

For recent work on the Carmel Mission, a team accessed a damaged wall via an interior passageway and inspected the previous restoration work that was finished to look new, but did not look ‘right,’ and likely would not perform well.

“I believe my purpose today is to convince the groups working on these amazing structures to repair the structure, but give it its timelessness, using the techniques of old—earth pigments and aged limewater over the slaked lime finish coat,” explained restoration specialist, Michael Ruiz.

Previously, Ruiz had worked on an 1870s-era historical home in Orange County to remove topcoats of paint covering up an original mural. He remembers carefully rubbing at the painted plaster to reveal a landscape scene viewed from a hilltop perspective.

Using lime paint wash as the topcoat.[5]
Using lime paint wash as the topcoat.

Another Southern California restoration specialist, Thom Susko of The Home Plaster Shop, came across problems with portland cement repairs performed on a job in Old Town San Diego. He restored the building using lime plaster and lime paint. Susko says portland cement was not suited for the historic adobe building because the plaster does not bond to un-stabilized adobe brick. Further, portland cement is less porous and harder than adobe, which is hygroscopic and needs to ‘breathe.’

For example, the restoration work at Mission San Juan Capistrano strives to reproduce the original construction of the walls as closely as possible. On the historic landmark’s website, it says:

To reinstate the historic character of this area, removal of all inappropriate past repairs, mainly the use of cement, is a key element to the project. Work on the masonry columns includes the removal of hard cement mortar[6] at the joints between the bricks and repointing with a softer, more compatible lime mortar.

Architects and specifiers should select lime-based products to restore, repoint, and re-plaster deteriorated masonry that would initially have been built with lime.

This type of job is commonly bid with known portions’ firm price, but with allowance in the budget for possible change orders—a fact of life on these projects. Using ‘time and materials’ would be more appropriate for especially difficult and unpredictable portions of projects. Thom Susko said the state project he worked on in San Diego did not have a specification—it was a moving target until he wrote the Request for Proposal (RFP) document. He further went on to say the state does have strict requirements, necessitating a bond, insurance, and its prevailing wage.

The exterior corridor at San Fernando Rey de España. Photograph © Robert A. Estremo, 2004. Photo licensed under Creative Commons Attribution-Share Alike 2.0.[7]
The exterior corridor at San Fernando Rey de España.
Photograph © Robert A. Estremo, 2004. Photo licensed under Creative Commons Attribution-Share Alike 2.0.

Products available for Mission restoration
The softness, breathability, and protective qualities of lime mortars, lime plasters, and lime washes makes them suited for restoration of Missions and other buildings of similar construction. There are several products that have established themselves in this niche.

Many U.S. companies import European seasoned-slaked lime mortars, plasters, and lime washes, produced in much the same way as those used by Vitruvius in Ancient Rome. Seasoned-slaked lime indicates the cooked limestone has been slaked with water and allowed to fully hydrate naturally over the course of months or years. Other dry, powdered products based on a more modern hydration process are also now available in the United States. These may be less expensive than seasoned-slaked lime products, but are more prone to popping and pitting due to incomplete hydration, and do not have the same working characteristics.

Some ready-to-use lime mortars are made more water-resistant through the addition of brick dust
(i.e. coccio pesto)—a technique consistent with that used for reservoirs and fountains in the California Missions, which also often employed hydraulic lime stucco (i.e. accelerated setting) made pink by the admixture of ground terra cotta tiles (another Vitruvian formula). Additionally, coccio pesto was used on architectural elements, such as the ladrillo colonnade columns at Mission Santa Ines.

Lime washes (or lime paints) are a suitable finish coat over a lime mortar, as they beautify, add color, and cross-link with the lime mortar to provide a water-shedding topcoat. The material gives a smooth coating which, after an initial wetting, encourages rainwater to run off. At the same time, the nature of this surface allows good, all-over evaporation to help the wall dry out. Lime wash is also unaffected by ultraviolet (UV) rays in sunlight that can damage synthetic paints. (See Stafford Holmes and Michael Wingate’s Building with Lime [ITDG Publishing, 2002].) Lime paints are commonly applied by plasterers, who are often more familiar with lime products than painters.

Lime plasters can also be used as topcoats over lime mortars, when smooth textures and a more substantial color coat is desired. The plaster is extremely strong, but pliant—the result is reduced cracking versus portland cement as a building shifts or walls expand and contract in response to natural temperature or moisture fluctuations. Further, lime plaster and earthen materials expand and contract similarly. As a result, when lime plaster is applied on an earthen wall or plaster, it is less likely to crack or peel off. (See Cedar Rose Guelberth and Dan Chiras’ The Natural Plaster Book [New Society Publishers, 2003].) Manufacturers should be consulted for detailed guide specifications, as lime cures more gradually than cement, and requires construction teams to schedule and protect the lime plaster work in different ways from what they may be used to.

For his La Casa de Bandini project in Old Town San Diego, Susko specified seasoned-slaked lime plaster and lime paint. Dating back to 1829, this adobe structure had been mistakenly repaired using portland cement plaster, had damage, and required a compatible finish plaster coat to allow the building to reach its full lifespan.

Lime stone wall during restoration using the lime mortars. Photos courtesy Merlex[8]
Lime stone wall during restoration using the lime mortars.
Photos courtesy Merlex

“The use of a product specifically formulated as a finish product will greatly aide in meeting the requirement of decorating the lime finish with lines to replicate stone,” he explains. “Additionally, the use of lime paint with good abrasion resistance and documented vapor permeability will greatly help with long-term maintenance.”

Lime products have recently captured an increasing share of the U.S. market for high-end, differentiated plasters in new construction. These products can crack less, breathe more, and give a more natural stone-like appearance than portland cement products. Lime plasters are especially popular with straw bale, rammed earth, and cob structures, as well as on new Italianate custom homes and resorts.

Restoration work can be especially rewarding—the chance to research, analyze, and repair a structure to its original function is both more challenging and different than an architect or specifier’s normal work. When it comes to plaster restoration, it is critical to find an experienced contractor who understands the historical perspective of the project, and take an active role in selection of plaster products compatible with the structure, as this is vital to the longevity of the repair. (Places to search for specialized architects and contractors include[9],[10],[11], and[12].)

Nick Brown, CEPE, is president of Vero Fine Italian Plaster Finishes and Merlex Stucco. Born in Sydney, Australia, he immigrated to the United States in 1979, and lives in Southern California, where stucco and plaster are predominant. Brown’s 14 years in the building materials industry includes experience with stucco, Venetian plaster, gypsum wallboard, and joint treatment products. He also serves as president of the Stucco Manufacturers Association, and holds the Certified Energy Plan Examiner (CEPE) credential for performing energy efficiency calculations in the State of California. Brown holds a BA from Princeton University and an MBA from the Ross School of Business at the University of Michigan. He can be contacted at[13].

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