Stucco: What to Look For

Read Part 1 of this installment »

Because building owners knew stucco to be a protective, but also somewhat fragile coating, they employed a variety of means to prolong its usefulness. The most common treatment was to whitewash stucco, often annually. The lime in the whitewash offered protection and stability and helped to harden the stucco. Most importantly, it filled hairline cracks before they could develop into larger cracks and let in moisture. To improve water repellency, stucco buildings were also sometimes coated with paraffin, another type of wax, or other stucco-like coatings, such as oil mastics. 

Stucco Deterioration

Most stucco deterioration is the result of water infiltration into the building structure, either through the roof, around chimneys, window and door openings, or excessive ground water or moisture penetrating through, or splashing up from the foundation. Potential causes of deterioration include: ground settlement lintel and door frame settlement, inadequate or leaking gutters and downspouts, intrusive vegetation, moisture migration within walls due to interior condensation and humidity, vapor drive problems caused by furnace, bathroom and kitchen vents, and rising damp resulting from excessive ground water and poor drainage around the foundation. Water infiltration will cause wood lath to rot, and metal lath and nails to rust, which eventually will cause stucco to lose its bond and pull away from its substrate.

After the cause of deterioration has been identified, any necessary repairs to the building should be made first before repairing the stucco. Such work is likely to include repairs designed to keep excessive water away from the stucco, such as roof, gutter, downspout and flashing repairs, improving drainage, and redirecting rainwater runoff and splash-back away from the building. Horizontal areas such as the tops of walls or chimneys are particularly vulnerable to water infiltration, and may require modifications to their original design, such as the addition of flashing to correct the problem.

Previous repairs inexpertly carried out may have caused additional deterioration, particularly if executed in portland cement, which tends to be very rigid, and therefore incompatible with early, mostly soft lime-based stucco that is more “flexible.” Incompatible repairs, external vibration caused by traffic or construction, or building settlement can also result in cracks which permit the entrance of water and cause the stucco to fail. 

Before beginning any stucco repair, an assessment of the stucco should be undertaken to determine the extent of the damage, and how much must be replaced or repaired. Testing should be carried out systematically on all elevations of the building to determine the overall condition of the stucco. Some areas in need of repair will be clearly evidenced by missing sections of stucco or stucco layers. Bulging or cracked areas are obvious places to begin. Unsound, punky or soft areas that have lost their key will echo with a hollow sound when tapped gently with a wooden or acrylic hammer or mallet. 

The Cure

Analysis of the original stucco will provide useful information on its primary ingredients and their proportions, and will help to ensure that the new replacement stucco will duplicate the old in strength, composition, color and texture as closely as possible. There are, however, simple tests that can be carried out on a small piece of stucco to determine its basic makeup. 

Some plasterers began using portland cement in the 1880s, yet others may have continued to favor lime stucco well into the early twentieth century. While it is safe to assume that a late-eighteenth or early-nineteenth century stucco is lime-based, late-nineteenth or early-twentieth century stucco may be based on either lime or portland cement. Another important factor to take into consideration is that an early lime-stucco building is likely to have been repaired many times over the ensuing years, and it is probable that at least some of these patches consist of portland cement. Once the extent of damage has been determined, a number of repair options may be considered. Small hairline cracks usually are not serious and may be sealed with a thin slurry coat consisting of the finish coat ingredients, or even with a coat of paint or whitewash.

The color of most early stucco was supplied by the aggregate included in the mix–usually the sand. Sometimes natural pigments were added to the mix, and eighteenth and nineteenth-century scored stucco was often marbleized or painted in imitation of marble or granite. Stucco was also frequently coated with whitewash or a colorwash. This tradition later evolved into the use of paint, its popularity depending on the vagaries of fashion as much as a means of concealing repairs. Because most of the early colors were derived from nature, the resultant stucco tints tended to be mostly earth-toned. This was true until the advent of brightly colored stucco in the early decades of the twentieth century. 

Many stucco buildings have been painted over the years and will require repainting after the stucco repairs have been made. Limewash or cement-based paint, latex paint, or oil-based paint are appropriate coatings for stucco buildings. The most important factor to consider when repainting a previously painted or coated surface is that the new paint be compatible with any coating already on the surface. 

Stucco construction is a hallmark of our Old Florida heritage. Taking good care of your historic house can be a source of beauty and pride, as well as a protection of your investment.

This article is sourced from Preservation Brief 22 of the U.S. National Park Service.

South Florida Stucco

Stucco is found on many historic homes throughout South Florida and along the Treasure Coast. Stucco is a two- or three-part exterior plaster coating applied directly onto masonry, or applied over wood or metal lath to a wood frame or even log structure,  and is primarily used on residential buildings and relatively small-scale commercial structures. Stucco is actually so common that it frequently goes unnoticed, and is often disguised or used to imitate another material.

Popularity

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. As a weather-repellent coating, stucco protected the building from wind and rain penetration, and also offered a certain amount of fire protection.

The introduction of the many revival styles of architecture in the United States around the turn of the twentieth century, combined with the improvement and increased availability of portland cement, resulted in a “craze” for stucco as a building material. 

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.

Although stucco buildings were especially prevalent in South 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.

Our Concerns

Age and lack of maintenance hasten the deterioration of many historic stucco buildings. Like most older building materials, stucco is at the mercy of the elements, and even though it is a protective coating, it is also particularly susceptible to water damage. It is also sometimes incorrectly viewed as a sacrificial coating, and consequently removed to reveal stone, brick, or logs that were originally never intended to be exposed.

Stucco on historic buildings is especially vulnerable not only to the wear of time and exposure to the elements, but also at the hands of well-intentioned “restorers,” who may want to remove stucco from eighteenth and nineteenth century structures, to expose what they believe to be the original or more “historic” brick, stone or log underneath.

A material of deceptive simplicity, stucco in most cases should not be repaired by a property owner unfamiliar with the art of plastering. Successful stucco repair requires the skill and experience of a professional plasterer.

Stay tuned for next installment: What to Look For »

This article is sourced from Preservation Brief 22 of the U.S. National Park Service.