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Stucco The Preservation and Repair of Historic Stucco

November 30, 2017

Stucco

The Preservation and Repair of Historic Stucco

  

The term "stucco" is used to describe a type of exterior plaster applied as a two- or three-part coating directly onto masonry, or applied over wood or metal lath to a log or wood frame structure. Stucco is found in many forms on historic structures throughout the United States. It is so common, in fact, that it frequently goes unnoticed, and is often disguised or used to imitate another material. Historic stucco is also sometimes incorrectly viewed as a sacrificial coating, and consequently removed to reveal stone, brick or logs that historically were never intended to be exposed. Age and lack of maintenance hasten the deterioration of many historic stucco buildings. Like most historic building materials, stucco is at the mercy of the elements, and even though it is a protective coating, it is particularly susceptible to water damage. Stucco is a material of deceptive simplicity; in most cases, its repair should not be undertaken by a property owner unfamiliar with the art of plastering. Successful stucco repair requires the skill and experience of a professional plasterer. Although several stucco mixes are representative of different periods, they are provided here for reference.  Each project is unique, with its own set of problems that require individual solutions.

 

  

Historical Background 

  The stucco on the early-19th century Richardson-Owens-Thomas House in Savannah, Georgia, is a type of natural cement. 

Stucco has been used since ancient times. Still widely used throughout the world, it is one of the most common of traditional building materials. Up until the late 1800s, stucco, like mortar, was primarily lime-based, but the popularization of Portland cement changed the composition of stucco, as well as mortar, to a harder material. Historically, the term "plaster" has often been interchangeable with "stucco"; the term is still favored by many, particularly when referring to the traditional lime-based coating. By the 19th century "stucco," although originally denoting fine interior ornamental plasterwork, had gained wide acceptance in the United States to describe exterior plastering. "Render" and "rendering" are also terms used to describe stucco, especially in Great Britain. Other historic treatments and coatings related to stucco, in that they consist (at least in part) of a similarly plastic or malleable material, include: parging and pargeting, wattle and daub, "cob" or chalk mud, pise de terre, rammed earth, briquete entre poteaux or bousillage, half-timbering, and adobe. All of these are regional variations on traditional mixtures of mud, clay, lime, chalk, cement, gravel or straw. Many are still used today.

  

The stucco on the early-19th century Richardson-Owens-Thomas House in Savannah, Georgia, is a type of natural cement. 

The stucco finish on Arlington House, Arlington, Virginia, was marbleized in the 1

Revival Styles Promote the Use of Stucco

The introduction of the many revival styles of architecture around the turn of the 20th century, combined with the improvement and increased availability of Portland cement, resulted in a craze for stucco as a building material in the United States. Beginning about 1890 and gaining momentum into the 1930s and 1940s, stucco was associated with certain historic architectural styles, including: Prairie; Art Deco and Art Moderne; Spanish Colonial, Mission, Pueblo, Mediterranean, English Cotswold Cottage, and Tudor Revival styles; as well as the ubiquitous bungalow and four-square house. The fad for Spanish Colonial Revival, and other variations on this theme, was especially important in furthering stucco as a building material in the United States during this period, since stucco clearly looked like adobe.

Although stucco buildings were especially prevalent in California, the Southwest and Florida, ostensibly because of their Spanish heritage, this period also spawned stucco-coated, revival-style buildings all over the United States and Canada. The popularity of stucco as a cheap and readily available material meant that, by the 1920s, it was used for an increasing variety of building types. Resort hotels, apartment buildings, private mansions and movie theaters, railroad stations, and even gas stations and tourist courts took advantage of the "romance" of period styles, and adopted the stucco construction that had become synonymous with these styles.

  

 

The damage to this stucco appears to be caused by moisture infiltration.

A Practical Building Material

Stucco has traditionally been popular for a variety of reasons. It was an inexpensive material that could simulate finely dressed stonework, especially when scored or lined, in the European tradition. A stucco coating over a less finished and less costly substrate, such as rubblestone, fieldstone, brick, log or wood frame, gave the building the appearance of being a more expensive and important structure. As a weather-repellent coating, stucco protects the building from wind and rain penetration, and also offers a certain amount of fire protection. While stucco was usually applied during construction as part of the building design, particularly over rubblestone or fieldstone, in some instances, it was added later to protect the structure, or when a rise in the owner's social status demanded a comparable rise in his standard of living.

Composition of Historic Stucco

Before the mid-to late 19th century, stucco consisted primarily of hydrated or slaked lime, water and sand, with straw or animal hair mixed in as a binder. Natural cements were frequently used in stucco mixes after their discovery in the United States during the 1820s. Portland cement was first manufactured in the United States in 1871, and it gradually replaced natural cement. After about 1900, most stucco was composed primarily of Portland cement, mixed with some lime. With the addition of Portland cement, stucco became even more versatile and durable. No longer used just as a coating for a substantial material like masonry or log, stucco could now be applied over wood or metal lath attached to a light wood frame. With this increased strength, stucco ceased to be just a veneer and became a more integral part of the building structure.

  

 

Caulking is not an appropriate method for repairing cracks in historic stucco. 

Today, gypsum, which is hydrated calcium sulfate or sulfate of lime, has, to a great extent, replaced lime.  Gypsum is preferred because it hardens faster and has less shrinkage than lime. Lime is generally used only in the finish coat in contemporary stucco work.

The composition of stucco depends on local custom and available materials. Stucco often contains substantial amounts of mud or clay, marble or brick dust, or even sawdust, and an array of additives ranging from animal blood or urine, to eggs, keratin or gluesize (animal hooves and horns), varnish, wheat paste, sugar, salt, sodium silicate, alum, tallow, linseed oil, beeswax, and wine, beer or rye whiskey. Waxes, fats and oils were included to introduce water-repellent properties, sugary materials reduced the amount of water needed and