Exterior Plastering aka “stucco” is among the oldest crafts in building construction.

Imagine if you will, early man huddled in the pouring rain under tree limbs that he had gathered to provide himself protection. It did not take long before it occurred to him, that he could further insulate himself from the elements, by interweaving smaller twigs and reeds into the larger branches, which could then be covered with mud or clay. This is stucco in its most raw and ancient form.

From those humble beginnings ancient civilizations saw the important value of stucco. The Egyptians used a plaster mix of gypsum, lime, sand and water to provide a smooth base for hieroglyphs that still tell their stories in the ruins of the pyramids. The Greeks happened upon the process of making a cementitious binder from a process of burning limestone in large kilns. This was not an easy process in that the fires used to heat the limestone had to reach a core temperature of 2200° F to transform the rock into its byproducts of calcium oxide, carbon dioxide and steam. More commonly called quicklime or lumplime, the calcium oxide is ground into a powder that once combined with water in a process called “slaking” provides a basic binder or “lime putty” for the plaster. The slaked lime which took on the consistency of heavy cream was then typically stored and covered in a pit sometimes for months or even years to ensure that it had become fully hydrated. Nobody is quite sure who discovered this process, but it has been documented that some of these pits were passed down from generation to generation. The Romans who also understood the processes of making lime putty, forbid its use unless it could be documented that was more than three years old.1

On the other side of the world the Mayans constructed their pyramids mostly out of rubble rather than cut stone. This was then covered with a thick layer of lime stucco that was smoothed and then painted a near blood red in color.

Although the predominant binder for most stuccos continued to be lime putty all the way up until the 19th century, the Romans are often credited with the discovery of a natural cement binder used for stuccoing many ancient wonders. Pozzolana is a sandy volcanic ash that was found near the town of Pozzuoli on the Bay of Naples. What they discovered was that when Pozzalana was combined with powdered hydrated lime and water, cement was created that was impervious to moisture. Its implications in use are probably most dramatically seen in the Aqueducts of Rome where the stucco was plastered directly over the conduits through which water was transported. Other ancient Roman edifices that were decorated with stucco include the Colosseum, the Forum and the Roman Baths. Walls covered with this decorative and durable material were called opus caementicium, deriving the current use of the word cement.2

While the Romans were perhaps beyond their time in using hydraulic cements, the use of lime putty plaster continued to flourish throughout the ages. Perhaps the most influential use of the product is retained in much of the established old European architecture. Over time, lime putty stucco was often used over a latticework of wood stakes covered with sand, clay and oftentimes animal dung (Wattle and Daub), to seal, protect and finish. Because the lime finish is not as durable as today’s cement plasters, it must be regularly sealed with a lime based white wash. Some speculation exists that this type of construction provided the basic knowledge for current lath and plastering systems.

The term “Stucco” is uniquely American in is use. Somewhere along the line, the correct terminology was forgotten or confused. By its European origins, stucco actually refers to interior ornamental plastering. “Render or rendering” is the proper term used to describe exterior plaster work, although you may hear the terms “parging, parget or pargeting used as well.

Stucco in early America was similar to its European counterparts in the use of lime-putty composition. Some examples of early American stucco include Monumental Church in Richmond, VA (1812), St. John’s Church, Washington D.C. (1816) and the Reformed Church of Saugerties, Saugerties NY (1852).3 St. John’s Church is particularly notable because it was designed by the man revered as the “Father of American Architecture,” Benjamin Henry Latrobe. Latrobe was appointed by Thomas Jefferson as the Surveyor of Public Buildings.4 Thomas Jefferson himself understood the value of stucco using it over brick and then scribing it to assimilate cut stone at Monticello, the estate that he worked on for over 54 years of his life.

Latrobe in his capacity as a public servant oversaw the building of the capitol and whiles not the original architect of the White House, he was largely responsible for its expansion. A misconception is that the White House is covered with stucco. In actuality, the porous sandstone that covers the building was painted with a mixture of lime, rice glue, casein and lead.

Naturally occurring cement was discovered in the United States in 1820. These cements were sometimes used in early stucco mixes to quicken the set. The discovery of natural cement enabled the building of large structures such as the Erie Canal, the Washington Monument and the Brooklyn Bridge among other important edifices. It wasn’t until 1871 that portland cement was first manufactured in the United States although it did not become widely available until the turn of the century.5

Stucco gained in popularity from the latter part of the 18th century due to the influence of revival architectural styles. An early example of stucco in Minnesota is the Strauss House in Hastings. Built in 1875, the mansard roofed home is an example of late Victorian architecture in the Greek Revival style. Popularity for the revival style of architecture continued to increase in use through the 1930’s and 40’s. Probably the best examples of stucco in its early use in the Twin Cities can be seen on historic Summit Avenue in St. Paul. Stucco’s influence can also be seen on the Prairie, Art Deco and Art Moderne styles of that era but also lent itself well to the Spanish Colonial, Mission, and Mediterranean styles popular on the West Coast. In his lifetime the revered architect Frank Lloyd Wright admired stucco for his “organic architecture” because he could design in clear geometric forms. This is evident on his first all stucco house, the Frank W. Thomas House (1901), Oak Park, Illinois and carried through on many major projects to one of his last great works, the Marin Civic Center, San Rafael, California (1957)
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In Minneapolis and St. Paul, stucco has been a mainstay for over a century. It is unmistakable in its character in the small bungalows that use a mix of brick or stone accents adding a charm that is unique to the Twin Cities. This is evident on nearly every street that you might wonder off the beaten path. Many old-timers in fact indicate that it was not unusual in its heyday for stucco to be installed all the way up and down an entire street when the weather was accommodating, then switched to interior gypsum plaster work when the weather was less accommodating. The romance with stucco continues today in and around the Twin Cities with many new houses and developments that stretch from Stillwater from the East of St. Paul, to Victoria in the western suburbs of Minneapolis.

1. Barbara Jones, “Working with Lime,” http://www.oikos.com/library/naturalbuilding/lime.html
2. R. Siddall, Lime Cements, Plasters, Mortars and Concretes, 2000, University College London, http://www.ucl.ac.uk/~ucfbrxs/limes/G123notes.htm
3. Jack Innis, “Defining Stucco,” Traditional Masonry, Fall 2007, http://www.traditionalmasonry.com/Articles/203/ 203-defining_stucco.cfm
4. Anne Grimmer, “The Preservation and Repair of Historic Stucco,” Preservation Briefs, article number 22, Technical Preservation Services, National Park Service, U.S. Department of the Interior, 1990. http://www.nps.gov/history/ hps/tps/briefs/brief22.htm
5. Michael P. Edison, “The American Natural Cement Revival,” ASTM Standardization News, January 2006

The term “stucco” is uniquely American in its use. Stucco by its European origins refers to interior ornamental plastering. The proper term is actually “render or rendering.” However for the sake of familiarity, stucco is also known as portland cement plaster. Stucco is a combination of a binder of portland cement, sand aggregate, hydrated lime, chopped fiber and water, which when mixed together makes a plastic mass that is workable. This can be applied by hand or machine to substrate surfaces of solid masonry or concrete; or over expanded metal lath installed over a water-resistive barrier and sheathing that has been attached to structural framing. The traditional application of stucco is a three-coat process consisting of the first coat or “scratch coat,” a second coat called the “brown coat” and final or “finish coat.” After initial set and cure, stucco in its hardened state is an exceptional cladding material that remains durable for decades.

The basic compositional characteristics of stucco a.k.a. portland cement plaster has remained relatively the same for over a century. Advances however have come in the standards for materials and modern technology that have improved the quality of the end product:

• Much improved manufacturing and quality of cements.
• Coalescing materials: Animal hair has been replaced by synthetic fibers.
• Better grades of aggregate that are washed of deleterious contaminants and meet industry sieve requirements for best properties.
• Admixtures that provide better workability and durability as well as tensile and compressive strength.
• Pigments, natural and synthetic that are more stable.
• Factory prepared finishes that take the guesswork out of mixing.
• Compositional mixes that can be tailored to suit the project.
• Corrosion resistant lath and accessories.
• Codes, Standards and Guides