HALL Building Information Group LLC
Along with wood and clay-based masonry, cementitious materials have been primary building materials for most
of recorded human history. This can be attributed to the natural abundance of lime which, when mixed with water, formed a
paste that became a hard and durable material that could be used to cover a surface or to “stick” masonry together.
The basic concept of stucco has remained the same, although portland cement is the most common cementitious material
in use in today’s stucco compositions.
That was then, this is now
Stucco is a cladding technology that depends on the skill
and experience of applicators who were independent businesses and not part of a nationwide company like so many other building
products. While there were companies that manufactured the cementitious products, there were none that put the various components
together and made them available as systems. Applicators purchased the various ingredients, took them to the site, attached
the lath and lathing accessories, field-mixed the various cementitious materials, applied the scratch coat and brown coat,
and topped it off with a finish coat that was either gray, for subsequent painting, or white.
ASTM C 926,
Standard Specification for Application of Portland Cement Plaster, has served as the design and application standard
for stucco cladding for many years. Because no manufacturers “took responsibility” for stucco as a system, typical
installation details were lacking, as were manufacturer’s recommended specifications or extended manufacturer’s
warranties…just the contractor’s one-year period of correction after the date of substantial completion.
The emergence of EIFS
Many believe that stucco—also known as Portland-cement
plaster—and exterior insulation and finish systems (EIFS) are almost the same thing, partly because EIFS are sometimes
called synthetic stucco. EIFS trace their start to Europe, then came to the U.S. in the late 1960s and became popular as an
exterior cladding because they could be installed quickly and cost less to install than most other claddings.
coatings component of EIFS consists of blends of cementitious materials with polymers to improve application, performance
and durability. And due to the polymers and the board-insulation separation between the coatings and the structural support,
the popularity of EIFS was driven by the wide variety of colors available and the fact that control joints were not necessary,
as they were for stucco.
The EIFS market grew significantly, and life was good…at least for 30 years.
But in the 1990s, because of poor installation on residential projects, lack of manufacturer monitoring and an unwise East
Coast building code requirement, EIFS failures began occurring far too regularly. Drainable EIFS systems were developed, however,
in response to lessons learned.
It is this writer’s opinion that
the problems with EIFS can be attributed largely to the widespread notion that EIFS were cladding systems that could be applied
by anyone with a pick-up truck and a bit of labor, without undue attention to manufacturers’ instructions. This proved
disastrous for the EIFS industry, and the flight to other cladding types, especially stucco, nearly killed the EIFS industry.
Even today, there remain owners, architects, contractors, and other decision makers who will not select, specify or install
EIFS. Fear of cladding failure, mostly unwarranted, continues to haunt the EIFS industry today.
The stucco story
Stucco has not been without its own set of problems as well. Whenever
cementitious materials are used in any form or for any building element, control of cracking looms as an important design
and construction consideration. And where there are cracks, there will be water infiltration. So the success of stucco depends
on what happens to the water when it infiltrates the cracks.
Then there was the ever-persistent price-driven
pressure for application of stucco to be quicker and cost less. Thus arose the use of unskilled labor and attempts to make
stucco thinner as cost-reduction moves, which caused the stucco industry to suffer its own problems.
the last 10 years, the EIFS industry has consolidated into a smaller number of companies, many of which were original EIFS
makers that managed to survive the storm and, thanks to creative initiative, have reinvented themselves. In the process, EIFS
manufacturers absorbed stucco cladding into their portfolios, and now offer factory pre-blended materials, manufacturer’s
installation manuals, recommended details, specifications, and extended warranties.
materials deliver more precise mixtures, eliminating the need for field mixing that sometimes results in batch-to-batch variation
or batches that may not be appropriately balanced. Many applicators have changed from field-mixed ingredients to the pre-blended
option. At the same time, EIFS technology has influenced stucco materials, and the resulting “cross-pollination”
has produced a larger number of EIFS and stucco cladding options.
So what we have now are the same companies
that manufacture and warrant EIFS systems also manufacturing and warranting stucco systems. And these manufacturers have borrowed
from the EIFS technology to develop new types of stucco systems that are finding their way into projects. As a result, in
looking at a completed project from the outside, it’s hard to tell which is which (hint, stucco systems have control
The wall assembly systems
EIFS and stucco wall assemblies are supplied either as
face-sealed barrier types or drainage-plane types. The two types are defined by Building Sciences Corp., a building-sciences
consulting firm that offers a comprehensive resource on their website at www.buildingsciences.com, as follows.
Face-Sealed Barrier Type Wall Assemblies: “A building
enclosure rain-control strategy that relies on the exterior face of the enclosure to act as a perfect barrier to rain penetration.”
Drainage Plane Type Wall Assemblies: “Drainage planes … are designed
and constructed to drain water. They are interconnected with flashings, window and door openings, and other penetrations of
the building enclosure to provide drainage of water to the exterior of the building.”
three diagrams that follow below generically describe the three most common systems available. The individual components are
identified, and in some cases a commentary is provided. Only assemblies at stud walls are described; assemblies on concrete
masonry, cement board and insulated concrete forms are very similar, but are not included in these details. Obviously there
are variations among the various manufacturers, but the following are the basic components.
Wall Studs: Studs are usually either wood or cold-formed steel and must be sufficient to withstand the transfer of
the wind load acting on the exterior cladding. Manufacturer and code compliance should be confirmed for each application before
selection. Some systems may be recommended by the manufacturer and code-approved for residential applications only.
B. Sheathing: Glass-mat gypsum board and oriented strand board are the most commonly used sheathings
that are either screw attached or nailed. Manufacturer and code compliance should be confirmed for each application before
selection. Also, oriented strand board is sensitive to degradation due to water exposure.
Joint Treatment: Whether the joints are covered remains a point of contention among some architects and specifiers.
Some believe treatment is necessary, while others do not. It’s like insurance—how much protection is enough? It
is this writer’s opinion that joint treatment is value added to the wall that improves its resistance to air infiltration
and moisture penetration. The most prudent practice would be to follow recommendations of the manufacturer and warranty requirements.
D. Weather Resistant Barrier: Probably the most crucial component of the exterior wall is the
weather-resistant barrier that has the potential of being either an asset (air, moisture, and water stopped on the proper
side) or a liability (vapor stopped on the wrong side). Depending on the climate and location of the project, it is critically
important that this barrier be either an air barrier or a vapor barrier, and not a vapor barrier when only an air barrier
is required. Common barrier materials are asphalt-based building paper, rubberized asphalt membranes, or liquid-applied membranes,
depending on the application, moisture-vapor conditions, the cladding system selected, and the manufacturer’s warranty
For example, one manufacturer’s warranty changes from 10 years (materials and labor)
for its basic EIFS system to 15 year (materials, labor and drainage integrity) for its elite EIFS system if the company’s
liquid-applied membrane product and premium base coat, adhesive, and finish coat products are used in the assembly. At least
one manufacturer includes a drainage mat outside of the weather resistant barrier in one of its systems.
E. Additional Weather-Resistant Barrier: The building code usually requires two layers of the
weather-resistant barrier behind stucco when the studs are wood. The barrier may or may not be required by manufacturer.
F. Stucco Scratch Coat: Traditional coat of cementitious materials, with or without fiber reinforcement,
the surface of which is scratched to improve the bond with the brown coat. The scratch coat is reinforced with self-furring
expanded steel diamond mesh lath.
G. Stucco Brown Coat: Traditional coat of cementitious
materials, with or without fiber reinforcement, the purpose of which is to level the plane of the wall to receive the finish
H. Lap Seal: Typically the manufacturer’s standard details and products to
create a lap between the drainage strip and the weather resistant barrier.
I. Rigid Insulation:
Expanded polystyrene board insulation, with or without drainage channels, is the usual board insulation that is selected.
Other board insulation products are acceptable to some manufacturers. For the EIFS wall assembly, the board insulation is
usually adhered with adhesive that is applied in vertical ribbons to create a drainage plane at the back of the insulation.
For the stucco wall assembly and the insulated stucco wall assembly, the board insulation is held in place by the screw fasteners
used to attach the metal lath to the wall studs.
J. Insulated Stucco Base Coat: The composition of this layer for the insulated stucco wall assembly
varies among manufacturers. The base coat may be one coat or two coats (scratch and brown) of a cementitious material with
or without fiber reinforcement. The base coat is reinforced with either self-furring expanded steel diamond mesh lath or another
type such as the configuration shown in the detail.
K. EIFS Base Coat: Typically a factory-blended,
100 percent acrylic polymer applied without the use of cementitious materials. A first layer of the base coat is applied,
an alkali-resistant fiberglass reinforcing mesh is pressed into the wet coating, and then a second layer of the base coat
is applied over the mesh.
L. Primer: While not always required, some manufacturers recommend—and
will increase the warranty period—if a primer is applied before the finish coat.
Coat: Finishes include field-tinted and integrally colored acrylic coatings, elastomeric finishes and specialty finishes
such as simulated masonry and simulated metallic finishes. While not required for the EIFS wall assembly, control joints are
required for the stucco wall assembly and the insulated stucco wall assembly to limit cracking.
Drainage Track: Typically an extruded plastic profile with holes to allow water that infiltrates past the outermost
surface into the drainage plane to drain to the exterior.
A wide range of warranties are available for these three assemblies.
For example, the following warranties are those that are available from two major manufacturers (several other manufacturers
do not include specific warranty periods on their websites). The range in time is due to variations of the type and quality
of the finish coat selection.
|EIFS Wall Assembly:|
A||5 to 10 years without the company’s weather-resistant barrier|
10 to 12 years with the weather-resistant
|Manufacturer B||3 to 9 years without the company’s
10 to 12 years with the primer
|Stucco Wall Assembly:|
|Manufacturer A||10 to 12 years|
B||3 to 9 years without the company’s primer or weather-resistant barrier|
7 to 11 years with
the primer but without the weather-resistant barrier
5 to 11 years without the primer but with the weather-resistant
9 to 13 years with the primer and the weather-resistant barrier
Stucco Wall Assembly:|
|Manufacturer A||7 to 10
|Manufacturer B||3 to 9 years without the company’s
primer or weather-resistant barrier|
7 to 11 years with the primer but without the weather-resistant barrier
11 years without the primer but with the weather-resistant barrier
9 to 13 years with the primer and the weather-resistant
EIFS ace DOE study
A three-year study concluding in 2006 was conducted by the Oak
Ridge National Laboratory to confirm the performance of EIFS for insulating and moisture resistance when compared to brick,
stucco, concrete block, and cement board wall assemblies. The study, funded by the U.S. Department of Energy, continuously
monitored and recorded the side-by-side performance of typical wall assemblies over a 15-month period at Charleston, S.C.
The study can be found on the EIFS Industry Members Association at www.eima.com.
While it is always important to be cautious when drawing conclusions from such studies, the evaluation
indicated that EIFS performed somewhat better than the other wall assemblies in terms of moisture resistance and thermal performance.
So now that EIFS and stucco cladding technology has stabilized to some
extent, what are the issues ahead?
Several factors will influence future system options and offerings.
First, the evolution of building codes and the quest for energy-efficient building enclosures could exert a profound influence
on stucco, and primarily involves the thickness of the rigid insulation. Continuous insulation outside of the wood or metal
stud framing is becoming common, and will in all likelihood become a building-code requirement in the near future.
The issue is the performance of the fasteners that attach the metal lath through the insulation to the wall studs.
The plane of the stucco is supported by the fasteners, and as long as the insulation is 1 or 1 1/2 inches thick, there is
a reasonable expectation of successful performance. But what happens if the insulation thickness has to be 4 inches thick?
Will the screw fasteners still support the cantilever load of the stucco, or will another support device be required? This
condition needs to be researched and tested before we know what will need to be done.
The other issue is
a little more problematic. When the rigid insulation is attached with screw fasteners, the weather barrier between the insulation
and the wall is penetrated, resulting in numerous small holes through what is supposed to be a continuous protective barrier
against the adverse effects of nature. Because buildings are wrapped so tightly with weather barriers, the only place for
the vapor pressure to equalize is through the screw penetrations, and if the direction is into the building, air and vapor
infiltration could be substantial (water infiltration could be a concern under some conditions).
there is no way to estimate or calculate the magnitude of infiltration or exfiltration of the effect on the heating, ventilating
and cooling of a building.
Another weakness of the fasteners is that they constitute thermal breaks in
the efficiency of thermal performance.
It could be that in the near future, because of these issues, stucco
may suffer a setback because EIFS will become the preferred choice by necessity.
About the author
Walter R. Scarborough, CSI, SCIP,
AIA, is Dallas regional manager of Charlotte, NC based HALL Building Information Group LLC, and offers specifications consulting,
manufacturing consulting, and peer reviews. He is a contributing editor of Durability + Design, and is a registered
architect and specifier with more than 30 years of technical experience with many building types. He was director of specifications
for 10 of his 22 years with one of the largest architecture firms in the world.
Scarborough is revision
author for CSI Project Delivery Practice Guide; co-author of the college textbook Building Construction, Principles,
Materials and Systems; has written articles for periodicals; has taught college courses; has given presentations at local,
state, regional, and national conferences; is active in the Construction Specifications Institute at national and chapter
levels; is a past president of the Dallas CSI chapter; is a member of the Institute Education Committee; has CDT, CCS, and
CCCA certifications from CSI; received CSI’s J. Norman Hunter Memorial Award in 2008; and is an ARCOM MasterSpec Architectural
Review Committee member.
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