Stucco had its origins thousands of years ago as it was used on some of mankind’s most significant and historic structures. Today it sets a standard for energy conservation, sustainability and low maintenance. Because of its many features and benefits, stucco continues to be one of the nation’s most widely used sidings.
Stucco is accepted in virtually any design genre. Whether you’re interested in Colonial or Victorian, Southwest or Modern, or anything you want to express your individual style, stucco is very accommodating. Like the flat clean look? What about adding a little more curb appeal with quoins, keystones and other aesthetic elements? Stucco can also be combined with other natural building materials. Add a little stone or some cedar for a homier or more rustic charm. Stucco can give you the look you want, at a price that makes sense.
The rich dark hue of Aztec Red, to the brilliance of Starch White and everything in between. How about the old world ambiance of Tuscany? Or the mottled look of Adobe” Color can be field mixed to your specifications or it can be defined by manufacturer’s color charts.
Only limited by the imagination. Stucco finish coats can be manipulated from medium Sand to high build Glacier or Spanish Lace textures. Can’t make up your mind? Let us direct you to where you can view some of the more popular styles on-line.
Get out your hose and spray stucco; although you might be there a while. Contrary to popular belief, stucco is very water resistant. Professional testing conducted by the Northwest Wall and Ceiling Bureau and Florida Concrete and Products Association confirm this fact.
Here are some independent reviews of stucco’s water resistance.
Is stucco water resistant?
Yes. Stucco sprayed for over two hours with 112 gallons of water per hour at a pressure equal to a wind-driven rain showed no signs of moisture on the back of the stucco. [Source: Federal Testing Laboratories]
Does stucco drain?
Yes. Water sprayed into a designed opening at the top of a stucco wall assembly drains between the water-resistant barrier and the back surface of the stucco. [Source: Federal Testing Laboratories]
Can stucco be installed with an enhanced drainage plane?
Yes. Although it may not be necessary in every circumstance, enhanced drainage systems can be beneficial for complex homes with higher than average exposure with driven rain.
Is solar-driven vapor a problem with stucco?
No. Solar-driven vapor does not pose a substantial problem with stucco, when the right combinations of materials are used. [Source: University of Minnesota Building Physics and Foundations Research Programs]
Because stucco is monolithic (continuous with no seams, laps or breaks) it can rebuff the effects of high wind better than most claddings. We’ve all seen those horrible news stories where the hurricane or tornado has devastated a town or suburb. Not surprisingly, stucco homes on average seem to hold up much better. Studies conducted by the Florida Concrete and Products Association in May 2007 illustrate stucco’s effectiveness in holding out wind and rain at hurricane speeds of 155 mph for 4 hours and 180 mph for 24 hours.
Stucco is noncombustible. It is a Class I exterior cladding with a flame spread resistance rating of 0 and smoke developed rating of 0. The International Building Code recognizes that framed walls comprised of 7/8″ stucco on the exterior face and an interior thermal barrier of 5/8 Type X Gypsum Board provide a fire resistance rating of 1 hour. Lessons learned by California fires, such as the Laguna Beach Firestorm in 1993, the Oakland Hills Fire of 1991 and San Diego County, CA 2007, illustrate that stucco homes provide superior fire resistance over claddings of wood or vinyl.
Have you ever seen what golf ball size hail can do to vinyl siding? What about those pesky woodpeckers tapping on your neighbor’s cedar sided house? We dare you! Get out the weed wacker, stucco can take whatever Mother Nature and you can dish out!
Stucco’s mass and air barrier-like qualities make it the energy leader in keeping a home impervious to winter’s winds, but comfortably cool in summer’s heat. If your clients care about energy efficiency, saving money in the long run, and being environmentally friendly, let them know what industry experts say about stucco.
“Given that each siding material is performing at its best, and is properly installed, stucco is the best choice for efficiency.” [Source: Service Magic, a Fortune 500 company representing 43,000 contractors throughout the U.S.]
Experts agree that stucco is the right choice for low maintenance and life span are important.
Fact: In Minnesota 70% of all-stucco homes ever built are still standing.
Fact: Most experts rate the life of a stucco wall to be 50+ years.
Expert Opinion: The Minnesota Green Affordable Housing Guide states “…stucco is chosen for residences that require extremely low maintenance and have an anticipated life span of 50 years or more.”
Expert Opinion: In Sarah Susanka’s book, The Not So Big House, it states, “…stucco will last for decades, and would be easier and more cost-effective to maintain.”
Expert Opinion: On the DIY Network segment, “Choosing a Siding Material”, stucco was selected because most importantly, “standard stucco exteriors are low maintenance … lasting more than 50 years.”
Stucco is the leading cladding when rated for low maintenance, energy, efficiency and curb appeal.
Stucco’s market share, since 2000, has increased 29% making it the fastest growing siding choice in the U.S. As of 2005, 22% of all home buyers choose stucco.
The average dollar increase in single family homes since 2000 based on MLS sales.
*Fiber Board, Cement Board, Hardboard/Masonite, Other
The manufacturers of every siding product claim theirs to be green and sustainable. Some claims are partially true. Some are a stretch in definition. The following logic is used by Minnesota researcher Louise Goldberg. Evaluate stucco’s claim for yourself.
- Sustainable Criteria: Does it save energy?
Stucco’s Performance: Yes. Because of its thermal mass, appropriately installed stucco can conserve energy in summer.
- Sustainable Criteria: Does it have a long life?
Stucco’s Performance: Yes. Stucco homes have demonstrated durability with 100-year service lives.
- Sustainable Criteria: Is it structurally robust?
Stucco’s Performance: Yes. Stucco homes are more likely to survive storms, tornadoes, hurricanes, and hail.
- Sustainable Criteria: Does it contribute to the waste stream?
Stucco’s Performance: No. Stucco is recyclable at the end of its service life.
- Sustainable Criteria: Is it renewable?
Stucco’s Performance: Yes. By using recycled and/or naturally abundant raw materials and solar thermal energy (or equivalent) for its manufacture, stucco legitimately can claim to be a renewable material.
LIFE CYCLE COSTS
A life cycle cost study of stucco systems conducted on behalf of the British Columbia Wall and Ceiling Association, confirms that “stucco is cost effective over the anticipated life of the types of building studies. Good design and attention to detailing, combined with good workmanship that conforms to industry standards will result in a durable wall cladding assembly with stucco finish.”
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.
- Barbara Jones, “Working with Lime,” http://www.oikos.com/library/naturalbuilding/lime.html
- R. Siddall, Lime Cements, Plasters, Mortars and Concretes, 2000, University College London, http://www.ucl.ac.uk/~ucfbrxs/limes/G123notes.htm
- Jack Innis, “Defining Stucco,” Traditional Masonry, Fall 2007, http://www.traditionalmasonry.com/Articles/203/ 203-defining_stucco.cfm
- 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
- 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.
Wood Framing/Wood Sheathing
This is the most common application for residential construction. Typical wood sheathing substrates are Exterior Grade and Exposure I plywood, Exposure I Oriented Strand Board and Ligno Cellulosic Fiberboard (Bildrite). These products are typically gapped a minimum of 1/8″ between meeting edges to minimize the effects of moisture induced expansion, which can translate into cracks in the finished stucco. The International Building Code requires that these substrates be covered with a minimum of two layers of Grade D building paper prior to the installation of lath. The Minnesota State Building Code has amended this requirement for the residential code to allow for the use of other water-resistive barriers over wood based sheathings. Please see MNLPB publication Stucco in Residential Construction for specific information as it relates to residential applications. After installation of the water-resistive barrier, 3.4 lb. self furred galvanized lath is attached to the structural supports by various fastening methods. Stucco is installed in a three-coat process with a 3/8″ thick scratch coat. This is followed with a 3/8″ brown coat and finally a 1/8″ cementitious finish coat for a final thickness of 7/8″. If an acrylic finish is substituted in lieu of the cementitious finish the combined thickness of the scratch and brown coats should be 7/8″ prior to installing the finish coat. This is especially important if the stucco is included as part of a fire rated wall assembly.
Fault Tolerant Stucco System: The performance of any wall system is dependent on the individual wall components acting as a whole. Some materials work better together than others. What was discovered in our computer modeling research is that commonly used wall assembly materials can yield a corresponding range of hygrothermal behavior from outright failure to satisfactory performance. One such system that was determined to be fault tolerant and capable of accommodating a range of observed material properties without hygrothermal failure was a conventionally framed wall as described above, except that blown-in closed cell polyurethane foam insulation was used in the stud wall cavities in lieu of conventional fiberglass batt insulation.
Enhanced Drainage Stucco System
It has been illustrated that stucco does drain over a variety of water-resistive barriers, however some experts and the Builders Association of Minnesota (BAM) have concluded that an enhanced drainage plane is better. This is perhaps rooted in the discussion on water vapor transport. The philosophy being that it is important to decouple the stucco from the water-resistive barrier. Doing this, it is reasoned, prevents capillarity continuity (stucco is so tightly bonded with the housewrap that it [housewrap] loses the desirable properties of water resistance and drainage of incidental moisture). It also provides a clear and faster drainage path for incidental moisture to evacuate from in back of the stucco, and also aids in drying the wall. BAM has taken this practice one step further by requiring that their membership meet these qualifications as a best practice standard to meet criteria for their self-insurance program.
- How is a Drainage Plane Made?
A basic drainage plane is constructed by adding a drainage mat over the sheathing which has been previously covered with a water-resistive barrier (WRB). This is followed by asecond intermediary layer (generally Tyvek, garden cloth or similar) over the drainage mat and finally thelath and stucco.
LOCALLY AVAILABLE DRAINAGE MATS
- Three Dimensional Nylon Matrix:
Locally this has been sold under the name brands Home Slicker by Benjamin Obdyke, Waterway by Stuccoflex, Enkamat by Colbond among others. It typically comes in a roll39 inches wide and provides a drainage space of approximately 1/4″.
- Corrugated Polystyrene: Masonry Technology Incorporated makes Sure Cavity. This is a perforated, high impact polystyrene with a 3/16″ deep corrugated pattern to mitigate drainage. Both of the precedingproducts are also available with a spun bonded fabric facer to keep the freshly applied stucco out of the drainage plane.
Steel Framing / Gypsum Based Sheathing
Steel framing can also be sheathed with wood based sheathing substrates, however more often than not; steel framing is sheathed with gypsum based sheathing substrates. According to the International Building Code, sheathing other than wood-based must be covered with a water resistive barrier consisting of a minimum one layer of ASTM D226 asphalt felt. Considering the vulnerability of these sheathings however, the Minnesota Lath and Plaster Bureau recommends a two layer application of water-resistive barrier. After the installation of the water-resistive barrier, 3.4 lb. self furred galvanized lath is attached to the structural supports by corrosion resistant screws. Stucco is installed in a three-coat process with a 3/8″ thick scratch coat. This is followed with a 3/8″ brown coat and finally a 1/8″ cementitious finish coat for a final thickness of 7/8″. If an acrylic finish is substituted in lieu of the cementitious finish the combined thickness of the scratch and brown coats should be 7/8″ prior to installing the finish coat. This is especially important if the stucco is included as part of a fire rated wall assembly.
There is a great affinity between stucco and concrete block because they are very similar in composition. For this reason it is not unusual to apply stucco in a direct application to concrete block. The concrete should be straight, true and free of any residual dirt or laitance that can compromise the bond. A direct application to painted block is not recommended. Masonry joints should be flush to the face of the block and not struck. Three-coat application entails a 1/4″ scratch coat, a 1/4″ brown coat and 1/8″ of cementitious finish. If an acrylic finish is substituted in lieu of cementitious, the combined thickness of the scratch and brown coats should equal 5/8″.
Metal Lath over Concrete Block
For most Minnesota applications, metal lath attachment over concrete block has always been the preferred method regardless of the condition of the block. This is because the lath provides a redundant measure that ensures the integrity of the attachment of the stucco to the block and also gauges the final thickness of the application. This is important considering the thermal changes of the Minnesota environment. Like in direct applications, it is recommended that all of the masonry joints be flush and not struck. 3.4 lb. self furred galvanized lath is then attached to the masonry with corrosion resistant powder actuated fasteners in accordance with ASTM Standard C 1063. In this system the scratch coat is applied 1/2″ thick, followed by a brown coat of 1/4″ minimum thickness and a 1/8″ cementitious finish coat. If an acrylic finish is substituted in lieu of cementitious, the combined thickness of the scratch and brown coats should equal 7/8″.
Similar to concrete block, cast-in place concrete and stucco have a great affinity towards one another because they are similar in composition. Problems arise when the concrete is so dense that it lacks any absorbency which may limit the bond between the concrete and the stucco. Another issue that may affect the bond is any residual release oils that may remain on the concrete as a result of forming the walls. A simple power washing may be all that is necessary to remove any residual oils, however there are also cleaning products available that may aid in this process. Nonabsorbent surfaces may have to be abraded by sand blasting, wire brushing, grinding or acid etching to provide a surface acceptable for the application of stucco. Other options that may mitigate the bond may include applying a dash bond coat of stucco or a bonding agent prior to installing the scratch coat. Form ties or protrusions resulting from forming the concrete should be removed or chipped back to provide a flat surface ready for stucco. Three coat stucco application entails a 1/4″ scratch coat, a 1/4″ brown coat and 1/8″ of cementitious finish. If an acrylic finish is substituted in lieu of cementitious, the combined thickness of the scratch and brown coats should equal 5/8″. It is recommended that in any direct applied stucco installation, a trial application be installed and tested to determine the full installations viability.
Metal Lath over Cast-in-Place Concrete
For most Minnesota applications, metal lath attachment over cast-in place concrete has always been the preferred method regardless to the condition of the block. This is because the lath provides a redundant measure that ensures the integrity of the attachment of the stucco to the concrete and also gauges the final thickness of the application. This is important considering the thermal changes of the Minnesota environment. Like in direct applications, it is recommended that the wall be free of any residual forming oils and that any form ties or protrusions resulting from forming the concrete be removed or chipped back to provide a flat surface ready for stucco. 3.4 lb. self furred galvanized lath is then attached to the masonry with corrosion resistant powder actuated fasteners in accordance with ASTM Standard C 1063. In this system the scratch coat is applied 1/2″ thick, followed by a brown coat of 1/4″ minimum thickness and a 1/8″ cementitious finish coat. If an acrylic finish is substituted in lieu of cementitious, the combined thickness of the scratch and brown coats should equal 7/8″.
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