One-coat vs. Three-coat stucco vs. EIFS – Which is better?

cortez-stucco-systemsIf you’re a homeowner who’s looking to either redo or build your house with a stucco finish, it can be easy to get overwhelmed. I’m sure you’re running across a lot of different terms that may or may not make much sense to you. Three of them are probably “one-coat”, “three-coat”, and “EIFS”. If that’s the case, then this article is for you! In this article, I’ll explain the three different terms for stucco systems and help you make an informed decision on your stucco system choice.

Stucco Basics

Modern stucco is usually a mix of sand, Portland cement, lime and water, but may also consist of a proprietary mix of additives — including fibers and synthetic acrylics that add strength and flexibility. Stucco may be applied with three different systems and each system offers a different finished look and durability.

One-coat stucco systems, typically the fastest method, feature a base coat and finish coat, which is sometimes sprayed on. Three-coat, also known as hard coat, stucco systems feature two base coats and a finish coat, making them more bulky, heavy, and durable, than one-coat stucco finishes. An EIFS, or synthetic, stucco system features two coats of stucco on top of a foam insulation board and is durable if installed with a proper water drainage system.

Which Stucco System is the Best?

So, which one stucco system is better, you ask? Unfortunately, the answer isn’t that simple. To paraphrase Eleanor Roosevelt, “A mature person is one who does not think only in absolutes… who has learned that there is both good and bad in all people and in all things.” Well, I may not be mature, but I am sure that you, dear reader, are. So, to answer which one stucco system is the best in a mature manner, there really isn’t one “best stucco system.”

Now that we’ve got that out of the way, I’ll be happy to go over the different stucco systems and give you the pros and cons of using each one. I’ll start with the traditional stucco system, three-coat.

THREE COAT STUCCO

Three-Coat Stucco System: A Brief History

Stucco as a building material dates at least to the time of the early Greeks and Romans. It often contained marble dust, but over the centuries was mainly made of lime, sand and water. After the invention of Portland cement in the 1800’s, that became the standard binder for stucco (Portland cement is made from limestone, as is lime). Today’s stucco is usually cement, sand and water, although lime is also sometimes added.

Stucco is a durable, attractive, and weather-resistant building material. It was traditionally used as both an interior and exterior finish applied in one or two thin layers directly over a solid masonry, brick or stone surface. The finish coat usually contained an integral color and was usually textured for appearance.

Then with the introduction and development of heavy timber and light wood-framed construction methods, stucco was adapted for this new use by adding a reinforcement lattice, or lath, attached to and spanning between the structural supports and by increasing the thickness and number of layers of the total system. The lath added support for the wet plaster and tensile strength to the brittle, cured stucco; while the increased thickness and number of layers helped control cracking.

Modern Three-Coat Stucco

Since then, the traditional application of stucco and lath occurs in three coats — the scratch coat, the brown coat and the finish coat. The two base coats of plaster are either hand-applied or machine sprayed. The finish coat can be troweled smooth, hand-textured, floated to a sand finish or sprayed. This method is still widely used to this day. In addition, Three-coat stucco is recognized by IBC/IRC building codes and remains one of the most popular exterior stucco choices for both residential, multi-family, and commercial projects.

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The Three Coats of a Three-Coat Stucco System

  • Scratch Coat: The first layer of stucco in a three-coat system is called a scratch coat. It is spread over the wall with a trowel, usually a flat type with a smooth bottom, one straight edge and one edge with notches along it. The stucco is spread ¼” to ½” thick with the flat base of the trowel, allowed to set up slightly, then scratched with the notched side of the trowel or a corn broom to create horizontal ridges along the wall. That coat is allowed to cure for 36 to 48 hours.
  • Brown Coat: The second coat in a three-coat system is called the brown coat, taking its name because sand is usually added to the stucco mix to provide a rougher surface for a finish layer to go over and bind to. The brown coat is also applied with a flat trowel in a generally smooth fashion. Once the wall is covered and stucco starts to set, it is smoothed with a screed, a long wood or metal tool pulled down the surface to even out the stucco. This coat is 1/8” to 3/8” thick. It is also allowed to dry, or “cure”.
  • Finish Coat: The finish coat gives stucco its final texture. It is generally thinner, 1/8” to ¼” thick, but can be applied thicker for a rougher texture. This coat is finished to any desired texture. It can be smoothed with a trowel to an almost perfectly flat surface, roughed up with the trowel to create irregular peaks and valleys, or given a special treatment by letting it set a bit with small peaks, which then are smoothed slightly with the trowel edge to look like popcorn or cottage cheese.

Three-Coat Stucco System Advantages

  • Economical: Low installation and life-cycle costs with a system that will last decades with little maintenance.
  • Durable and impact resistant: Can withstand years of weather and physical abuse.
  • Cement-based: Fungus, rot, and insect resistant.
  • Fire-resistant: Non-combustible and available in 1-hour fire resistant rated assemblies.
  • Offers a variety of finishes: Stucco, acrylic, paint, and stone are all finish options.

For many years, the three-coat system was the only one recognized by most building codes, so that helps explain its popularity, as well. Another reason people like it is because it is the heaviest, densest, and strongest stucco system you can install on your home’s exterior. Of course, it will cost a little more because of this, too. Another advantage is that for stucco contractors, it can be easier to level if the home’s framing isn’t straight. And lastly, it is great for an “adobe” or Spanish territorial look that requires big, rounded corners.

I recommend Omega Products’ “Diamond Wall Three Coat” product if this is the stucco system you choose for your home or project. Diamond Wall Three Coat is an excellent choice for both scratch and brown coats. It is a factory prepared blend of Type I-II Portland cement, chopped fibers, and proprietary ingredients field mixed with sand, water, and an optional admix. After you apply these two coats, I recommend using Omega Products’ Akroflex as the finish coat. Click here for more info on finish coats.

EIFS (EXTERIOR INSULATION FINISH SYSTEMS)

EIF System: The Basics

EIFS, or Exterior Insulation Finish Systems, is a type of exterior wall covering that mimics the look of stucco, but isn’t technically stucco. The advantage of EIFS is that it adds an element of insulation and weather protection to your home’s exterior. In addition, EIFS can stand alone as a finish, or can be molded to replicate most any architectural style. It can also adhere to nearly every exterior wall surface. The disadvantage is it requires substantially different upkeep and installation from traditional stucco or other finishing systems.

Although often called “synthetic stucco”, like I said, EIFS is not really stucco. Traditional stucco is a centuries-old building material made of cement, sand, and water, and is a hard, dense, thick, non-insulating material. EIFS is a lightweight, synthetic wall cladding that includes foam plastic insulation and thin synthetic coatings. To function properly, EIFS needs to be architecturally designed and installed as a system.

There are a number of versions of EIFS. The most basic and common EIFS is called a barrier EIFS (also known as a traditional or conventional EIFS). Another type is called an EIFS with drainage, which is a barrier EIFS to which a water drainage system has been added.

EIF System: A Brief History

EIFS has been in use since shortly after World War II in Europe, where old masonry buildings were in need of further insulation and aesthetic upgrades. In the early 1950’s, insulation board and synthetic plaster both became popular and were eventually marketed together in Europe as early as 1963.Soon after, the technology became available in the U.S. as a finishing for commercial and, eventually, residential buildings. In the 1990’s, EIFS became controversial as cases began to surface in which improper installation caused water damage to homes.

Modern EIFS

The modern version of EIFS consists of 3 main parts:

  • Insulation board: The insulation board part of the EIF system is usually made of polystyrene or a similar material and is applied either manually or mechanically to the surface of an exterior wall. This board gives the system excellent energy efficiency, with many users reporting as much as a 55% decrease in air infiltration compared with wood and brick walls.
  • Base coat: The base coat involves a synthetic plaster reinforced with a fiberglass mesh.
  • Finishing coat: The final layer is the finish, which is decorative and waterproof and gives EIFS its stucco-like appearance.

EIFS Problems

The majority of problems that are reported with EIFS involve moisture damage — including mold, rot, and decay. These are usually due to improper installation. The problem begins if there is any air pocket at all between the insulation board and the sheathing. This issue becomes dangerous when water penetrates the synthetic plaster on the outer part of the EIFS. At this point, water is allowed to enter the airspace and remains for long periods of time, causing rot and decay. Usually, this is due to improper flashing and caulking during installation, or a lack of maintenance on the homeowner’s part.

Before beginning installation of EIFS, check the certifications and reputations of the builders you are hiring. Builder-accepted standards for EIFS installation exist, and shortcuts can lead to moisture entrapment years down the road. Often, many problems due to improper EIFS installation can be fixed easily and cheaply if caught early.

Next Generation EIFS

EIFS before 2000 was a barrier system, meaning the EIFS system itself was the weather barrier. After 2000 the EIFS industry introduced the air/moisture barrier that resides behind the foam. In a study done by the The Department Of Energy’s Office of Science – Oak Ridge National Laboratory it was found that the best air/moisture barrier was a fluid barrier. The National Institute of Standards and Technology (NIST) have evaluated the 5 life cycle stages of the environmental impact of EIFS alongside brick, aluminum, stucco, vinyl, and cedar. Depending on a variety of site and project specific conditions, EIFS has the potential to save money in construction costs and contribute toward energy efficient operations and environmental responsibility when correctly designed and executed.

EIFS Advantages

EIFS can resemble traditional stucco, while offering additional energy efficiency, design versatility, weatherablity, and durability. The usage of EPS foam offers excellent insulation and allows the applicator to economically create virtually any architectural detail or design.

If you’re going to choose EIFS as your “stucco” system, I would recommend Omega Products’ AkroFlex Exterior Insulation and Finish Systems. Their system is a lightweight, multi-component exterior wall assembly. AkroFlex EIFS can be finished in an unlimited array of colors and unique textures. The design versatility and finish options of AkroFlex EIFS make it a perfect choice for designers to create buildings with beautiful intricate detailing and distinctive appearances. Here are the main advantages…

  • Energy Efficiency: Reduces operating energy costs due to increased wall insulation and reduced air infiltration.
  • Design Flexibility: Can be fashioned into virtually any shape or design and is available is a wide selection of colors and textures.
  • Lightweight: Reduces the structural load requirements.
  • Weather Resistance: AkroFlex finishes and base coats are inherently weather resistant.
  • Durable: Fade, crack, abrasion, and dirt resistant.
  • Cost Effective: Offers economical detailing and low life cycle costs.

For these reasons, EIFS has become one of the most popular cladding options with billions of square feet installed on buildings around the world. AkroFlex EIFS is available in the following systems:

  • AkroFlex_Barrier_webAkroFlex Barrier EIF System: The AkroFlex Barrier EIF System is a Class PB barrier system designed to keep moisture on the outer surface of the wall and out of the wall cavity. AkroFlex Barrier consists of EPS foam board adhesively attached over approved, properly prepared sheathing. Base coat is applied over the foam board and fiberglass mesh is then fully embedded in the base coat. Lastly,100% acrylic finish is applied.

 

  • AkroFlex_WaterManaged_webAkroFlex Water Managed (WM) System: The AkroFlex Water Managed (WM) System is Class PB system utilizing a water-resistive barrier and a means of draining incidental moisture to the exterior. AkoFlex WM consists of a water-barrier applied over approved, properly prepared substrates. Grooved foam board is mechanically attached to the sheathing, and then base coat with mesh fully embedded is applied over the foam. Lastly, primer (optional) and AkroFlex 100% acrylic finish are applied. Like a standard PB system, AkroFlex WM’s finish and base coats are designed to keep moisture on the exterior surface, but WM adds an additional layer of moisture protection with a water-resistive barrier.

 

  • AkroFlex_WaterManagedPlus_webAkroFlex Water Managed Plus (WM+) System: The AkroFlex Water Managed Plus (WM+) System is a class PB system utilizing a water-resistive/air barrier coating and a means of draining incidental moisture to the exterior. AkroFlex WM+ consists of the AkroGuard/AkroFill water-resistive/air barrier coating system applied over approved, properly prepared substrates. Foam board is attached to the sheathing using vertical ribbons of adhesive. Then base coat with mesh fully embedded is applied over the foam. Lastly, primer (optional) and AkroFlex 100% acrylic finish are applied. Like a standard PB system, AkroFlex WM+’s finish and base coats are designed to keep moisture on the exterior surface, but WM+ adds an additional layer of moisture protection with a water-resistive coating.

ONE COAT STUCCO

One-Coat Stucco System: A Brief History

Like I mentioned earlier in this article, traditionally, three layers of stucco were applied to walls — the first layer being the scratch layer, the second layer a brown coat, and the third the hand-troweled finishing coat. Then I mentioned the EIF System, which isn’t really “stucco” at all, but the end product resembles a real stucco exterior.

The last stucco system I’ll talk about is one-coat stucco. Introduced in the mid-1980’s, the one-coat stucco is a newer application that is similar to traditional stucco. It’s called “one-coat” because you can technically apply only one coat and meet building code requirements. Most homeowners are also concerned about the look of their home as well as the function, so a second, finish coat, is usually applied. So, when it comes to real-world application, “one-coat” stucco is usually really a two-coat system, even though we still call it one-coat.

One-Coat Stucco: The Basics

Now that we have that straightened out, let’s get down to the basics of a one-coat stucco system. A one coat stucco system may be applied one of two ways:

  • Foam: Installing it this way uses the Styrofoam in place of the “scratch coat” that is typical in a three-coat stucco system.
  • No Foam: Installing it this way takes away the insulating layer of the foam. One reason to do it this way might be if you are applying the base coat directly to a masonry wall as opposed to a wood-frame construction wall.

The cement used in the one coat system is about 3/8 of an inch thick and is reinforced with fiberglass particles. Each one-coat system is a proprietary mix of Portland cement, fiber reinforcement and secret ingredients. As a blended proprietary mix, one-coat stucco manufacturers provide the extra training and instructions to ensure their products are used within their specific guidelines.

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One-Coat Stucco System Advantages

The one-coat stucco system offers design flexibility, durability, and water management. Additives such as acrylics and glass fibers are added to improve strength and flexibility and reduce cracking. It is a highly cost-effective and resilient alternative to the traditional three-coat stucco system. Other advantages include:

  • Low life-cycle costs: Will last decades with little maintenance.
  • Durable and impact resistant: Can withstand years of weather and physical abuse.
  • Cement-based: Fungus, rot, and insect resistant.
  • Fire-resistant: Non-combustible and available in 1-hour fire resistant rated assemblies.
  • Offers a variety of finishes: Stucco, acrylic, paint, and stone are all finish options.
  • Reduced labor costs: Only requires one base coat application.
  • Shorter construction schedule: Finish coat can be applied in as little as 24-hours after the brown coat.
  • Improved Energy Efficiency: Assembly’s R-value is increased when foam board is utilized.
  • Consistency: Factory blended mix requiring only sand and water to be added in the field.
  • Lower Weight: Reduces the exterior cladding weight by approximately 50% from three-coat stucco.

The one-coat stucco product I recommend is Omega Products’ Diamond Wall One Coat Stucco Systems. Diamond Wall One Coat Stucco Systems are code compliant plaster systems that create a long-lasting exterior cladding for residential and commercial projects. One-coat stucco has the appearance and advantages of traditional three coat stucco, but with increased energy efficiency, lower labor costs, and schedule savings.

Diamond Wall One Coat is available either as the Diamond Wall Insulating System, Diamond Wall System, or the Diamond Wall PM System. All three systems consist of a 3/8-inch minimum thick layer of Diamond wall base coat that is embedded in metal lath. A variety of finish options are available including ColorTek stucco, AkroFlex acrylic stucco, OmegaFlex acrylic stucco, AkroLastic elastomeric stucco, and AkroCoat paint finishes. I generally recommend using Akroflex for its elasticity and cost-effectiveness.

  • Diamond Wall One Coat System: The Diamond Wall One Coat System is applied over approved weather barrier and solid sheathing. The Diamond Wall base coat is a factory prepared blend of Type I-II Portland cement, chopped fibers, and proprietary ingredients field mixed with sand, water, and an optional admix.
  • Diamond Wall PM One Coat System: The Diamond Wall PM One Coat System offers an upgrade to current one coat stucco systems by providing improved crack resistance, flexural and tensile strength, and impact resistance. It uses Diamond Wall PM Concentrate and is fielded mixed with the liquid Diamond Wall PM Admix. The system is available as insulated and non-insulated.
  • Diamond Wall Insulating One Coat System: The Diamond Wall Insulating One Coat System includes a layer of foam board insulation that may be applied over open wall framing or optional sheathing. The foam board greatly increases the R-value of the wall assembly, which improves the energy efficiency of the building.

You can also get the Diamond Wall System “Sanded”, with sand already mixed in it, which is a little more expensive than buying the sand separately and field mixing it. The most expensive of your options will be the Diamond Wall PM One Coat System, because of the extra proprietary ingredients added in that add flexibility and tensile strength.

Here in the 4 Corners area, you’re usually going to see a one-coat insulating system being installed because of the time and cost savings this system provides, as well as the R-value and insulation the EPS foam will give you.

In general, I recommend using the Diamond Wall Insulating One Coat System for most residential uses. In fact, I wrote an article listing most of the materials you would need to eliminate 90+% of the pesky hairline cracks that drive owners of stucco homes crazy. It includes an added material and step to the process that you’re not going to find information on most places. Click here to read my article.

As always, feel free to give me a call or stop on by the ProBuild on County Road M and Highway 145 and ask for Derek.

derek-and-samDerek Alvarez sells stucco products and building materials at ProBuild here in Cortez, Colorado. If you have any questions for Derek, you can contact him at 970-739-9911.
*The views and opinions expressed are those of Derek Alvarez alone and do not necessarily represent the views of ProBuild.

What people are saying:

  1. I’m interested in learning more about EIFS and was interested in reading that it’s been used since shortly after World War II. You go on to mention that they used this because many buildings in Europe were needing more insulation and aesthetic upgrades. I wonder if EIFS can be used on any other type of house siding other than brick?

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