How to Fix and Preserve Old Stucco

A Summary of Preservation Brief 22

Stucco is an exterior plaster that can be layered over masonry, logs or wood lath, or metal. Preservation Brief 22, The Preservation and Repair of Historic Stucco not only provides information on the historical use of stucco but also practical guidance on when repairs are necessary and how to do patches.

"Stucco is a material of deceptive simplicity," writes author Anne E. Grimmer. "Successful stucco repair requires the skill and experience of a professional plasterer."  For many of you, read no more. But it's always a good idea to know what your contractor is doing, so here's a summary of Grimmer's guidance and expertise.

Note: Quotes are from Preservation Brief 22 (October 1990). Photos in this summary article are not the same as in the Preservation Brief.

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About Preservation Brief 22

Stucco Sided Home With Spanish Revival Influences
Stucco Sided Home With Spanish Revival Influences. Photo by Lynne Gilbert / Moment Mobile / Getty Images (cropped)

The Preservation and Repair of Historic Stucco was written by Anne E. Grimmer for the Technical Preservation Services of the National Park Service, the division of the U.S. Department of the Interior in charge of historic preservation. The information was first published in October 1990, but this brief still provides the best, non-commercial expert advice on how to fix stucco.

Grimmer's main points are these:

  • Stucco is a misunderstood material.
  • Sometimes people mistakenly remove stucco veneer from buildings to expose the brick or timber underneath.
  • Historically, stucco is meant to cover and protect what's beneath it.
  • Without maintenance, stucco siding is subject to water damage.
  • Repairs should be done by a skilled plasterer. Improper patching can cause more damage and more expense.

Continue below for a summary of each section, with links to the Brief 22 online.

Source: Preservation Brief 22. Download the PDF version of The Preservation and Repair of Historic Stucco, with more photos and diagrams, from the National Park Services website at nps.gov.

Stucco facade on Konigliches Schloss, Berchtesgaden, Bavaria, Germany
Stucco facade on Konigliches Schloss, Berchtesgaden, Bavaria, Germany. Photo by Tim Graham/Getty Images News Collection/Getty Images

Stucco is one of the oldest building materials, although its "recipe" has changed throughout the years. Artisans of the 18th century used a thick paste mixture to sculpt decorative interiors, like inside the Wies Church in Bavaria, and ornamental exteriors. By the 19th-century stucco was a common protective exterior siding throughout the US. The easily tinted and readily available stucco was less expensive than stone or brick but provided a rich, expensive-looking facade. Early stucco was lime-based (lime, water, and sand) and flexible. After 1820 natural cement like Rosendale was often added, and after 1900 Portland cement mixed with lime made for a more durable, strong, rigid, and versatile stucco. Today gypsum has replaced lime, although a lime mixture is often used for the final coating. Remember that stucco mixtures throughout the US were not standardized—local additives such as hooves, straw, and whiskey are often found in old stucco base coatings.

Spanish Revival and Mission Revival style homes are well-known for their stucco siding, which can visually mimic traditional adobe.

Methods of stucco application vary depending on the substructure. Generally, three layers are applied in a wet environment to create a solid bond—if moisture is pulled too quickly from the stucco, cracking can occur. The third layer, the "finish," has many variations.

Other Names for Stucco:

  • Plaster
  • Render or rendering (chiefly British)

Historically Influential Book:

  • The Architecture of Country Houses by Andrew Jackson Downing, 1850. Dover Publications Reprint
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Traditional Basque architecture in northern Spain, with stucco in disrepair
Traditional Basque architecture in northern Spain, with stucco in disrepair. Photo by Tim Graham/Getty Images News Collection/Getty Images

Historically, stucco was maintained with a lime whitewash, which reinforced the lime in the stucco and filled any hairline cracks that may have been present. Deterioration is almost always because of moisture compromising the stucco, so address the cause first.

Steps to Repairing Stucco:

  1. Determine the point(s) of moisture and fix the problem. Non-stucco repairs may include flashing, roof shingles, downspouts, or redirecting water runoff.
  2. Determine what type of stucco is present to "ensure that the new replacement stucco will duplicate the old in strength, composition, color and texture as closely as possible." Historic stucco made from sand and lime may not be available or appropriate. These days manufactured sand is used in place of traditional river sand. Gypsum and Portland cement are used in place of lime.
  3. Determine unstable stucco areas by tapping with a spoon. Patching is preferable to overall replacement.
  4. Prepare the area. "Proper preparation of the area to be patched requires very sharp tools..." 
  5. Prepare the stucco. Tint can come from the sand, cement, or pigment. Brightly colored stucco is often called "Jazz Plaster," as it was popular in the Jazz Age of the 1920s
  6. Anything can go wrong. Consider (1) the mixture, (2) how the materials were mixed (or over-mixed), and (3) how the stucco is applied. Old stucco should not be overlapped with new. New stucco should be a close match with ​the old mixture. Each coat should dry for 24-72 hours.
  7. If painting, use lime wash or cement-based paint, latex paint, or oil-based paint. Some paints require the stucco to be cured for up to a year. A water-repellent coating is rarely necessary.
  8. Cleaning stucco depends on what needs to be removed and what kind of surface it's on. Historic stucco can have a number of different textures, as explained in Preservation Brief 22.
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Yellow Stucco Farmhouse in Chester County, Pennsylvania
Stucco Farmhouse in Chester County, Pennsylvania. Photo by Robert Kirk / Moment Mobile / Getty Images (cropped)

"There are probably almost as many mixes that can be used for repair of historic stucco as there are historic stucco buildings," writes Anne E. Grimmer, author of Preservation Brief 22. Nevertheless, Grimmer gives a list of recipes to try for different coatings that may work for different historic time periods. More »

The invasive Giant African land snail can cause structural damage to stucco.
The invasive Giant African land snail can cause structural damage to stucco. Photo by Joe Raedle/Getty Images News Collection/Getty Images

Moisture is the cause of most stucco deterioration. Remove any causes before addressing stucco repairs.

Don't permanently remove stucco from buildings that were originally stuccoed. Even if stucco was applied after construction, it should rarely be totally removed. Stucco repairs should be patch jobs, with the new stucco matching the remaining stucco in "strength, composition, color and texture." More »

Here is a sampling of the reading list resources:

  • Plaster and Plastering. Mortars and Cements, How to Make, and How to Use... by Hodgson, Frederick T. Hodgson, 1901
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  • Introduction to Early American Masonry—Stone, Brick, Mortar and Plaster by Harley J. McKee, FAIA, The Preservation Press, 1980
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  • Portland Cement Plaster Stucco Manual, Portland Cement Plaster Stucco Manual, 2003
    Buy on Amazon
  • Plastering Skills by F. Van Den Branden and Thomas L. Hartsell, American Technical Publishers, 1985
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