Photograph of EIFS synthetic stucco exterior (C) Daniel Friedman Stucco Wall Methods & Choices - Best Practices Guide
     

  • STUCCO WALL METHODS & INSTALLATION - CONTENTS: Stucco building exteriors: drainage plane, installation, 3-coat stucco, thin coat stucco, EIFS, stucco painting. Stucco recipes. Three-coat stucco installation details. Metal lath based stucco wall installation. Thin coat stucco wall systems & installation. EIFS and synthetic stucco wall systems, success, issues, inspection, and problem diagnosis. The role of weather, moisture, temperature, cleaning, in stucco wall success or failure and stucco wall painting problems
  • POST a QUESTION or READ FAQs about different types of exterior wall stucco and stucco application methods
  • REFERENCES

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Stucco wall covering method choices, methods, & comparisons:

This article discusses types of stucco building exterior wall materials and installation methods, including stucco recipes, three-coat stucco installations, stucco wall expansion joints, metal-lath stucco systems, how stucco is applied to walls, thin coat stucco systems,

EIFS synthetic stucco wall systems, and the role of weather and moisture in stucco wall installation, durability, and painting success.

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Stucco Building Exteriors: Product Choices, Installation Details

Adapted/paraphrased with permission from Best Practices Guide to Residential Construction. Steven Bliss.

Antique stucco building, Frankfort Germmany (C) Daniel Friedman 1969Stucco on building exteriors, in its traditional form is a cementious coating, installed over wood lath or more recently over expanded metal wire lath. Stucco systems have been used for hundreds, and in some forms (mud over wood lath), for thousands of years.

[Click to enlarge any image]

Our photograph (left, Daniel Friedman) shows an antique stucco-walled building in Germany.

No stucco system is impervious to water penetration, whether traditional three-coat stucco, modern one-coat systems, or exterior insulation and finish systems (EIFS). Since water may enter through cracks, penetrations, or through the stucco finish itself, all stucco exteriors rely on a backup waterproof drainage plane to protect the structure.

The drainage plane under stucco is essentially the same as under other exterior claddings, with building paper layered to shed water and carefully integrated with all flashings at doors, windows, and other penetrations.

In addition, stucco systems need a weep screed or similar perforated flashing at the bottom of the wall to safely drain away any trapped water at the foundation. Without a continuous drainage plane, stucco systems are subject to serious water problems.

While older, traditional stucco walls were designed to get wet and readily dry out, the newer synthetic systems are less permeable to moisture. If trapped water cannot readily drain away or dry to the exterior, the underlying structure is more vulnerable to moisture damage.

This article series discusses best practices construction details for building exteriors, including water and air barriers, building flashing products & installation, wood siding material choices & installation, vinyl siding, stucco exteriors, building trim, exterior caulks and sealants, exterior building adhesives, and choices and application of exterior finishes on buildings: paints, stains.

This article series includes excerpts or adaptations from Best Practices Guide to Residential Construction, by Steven Bliss, courtesy of Wiley & Sons.

Stucco Building Wall Drainage Plane

Stucco exterior, Tucson Arizona (C) Daniel Friedman Our photograph (left) of a modern stucco exterior shows how stucco is used in the southwestern U.S., in this case Marana, outside Tucson, AZ.

Traditionally, stucco contractors have used Grade D building paper rather than asphalt felt when applying stucco to wood-frame walls. Grade D building paper is an asphalt-impregnated kraft-type paper, similar to the backing on fiberglass insulation.

Unlike asphalt felt, it is made from new wood pulp, rather than recycled material. It has water-resistance ratings ranging from 20 to 60 minutes, depending on the thickness.

Although the International Residential Code (IRC) does not specify a required rating for stucco underlayment, the trend in the industry is to use two layers of 15- or 30-minute Grade D paper, isolating one layer from direct contact with the stucco and creating a secondary drainage space in the gaps between the two layers.

Two layers are necessary, since the stucco tends to bond to the outer layer of building paper or plastic housewrap, compromising its water repellency. The wetter the climate, the heavier the paper should be. In coastal areas, some contractors use as much as two layers of 60-minute paper. The heavier papers provide better protection, but they are less flexible and more difficult to install.

Some contractors are starting to use plastic housewrap under stucco. How well it holds up in direct contact with stucco is in question. One option is to use plastic housewrap as the first layer and cover it with Grade D building paper, which has a longer track record in direct contact with stucco.

Stucco on Adobe (C) Daniel FriedmanOther than the building paper, flashings are essentially the same as with any other cladding system.

Metal or membrane pans are recommended at the bottoms of windows and doors. As with other cladding systems, it is critical that the building papers layer over window head flashings and that window pan flashings drain on top of the building paper.

Watch out: Do not caulk the horizontal joints at window head and pan flashings; this way, any trapped water can drain out.

To complete the system, the drainage plane behind stucco must have a perforated flashing called a “weep screed” at the foundation line. According to the IRC, this must be at least 4 inches above grade and must allow trapped water to drain to the outside of the building. Without a weep screed, the stucco tends to bond to the top of the foundation, creating a moisture dam.

Our photograph of stucco coating the exterior of an adobe structure (San Miguel de Allende, Mexico) demonstrates that on these traditional structures stucco was applied directly to the surface of adobe bricks.

Three-Coat Stucco Building Walls

Figure 1-29: Three-Coat Stucco (C) Wiley and Sons, S BlissThree-coat stucco using Portland-cement plaster has been used successfully in the United States for nearly 200 years.

It is applied about 7/8-inch thick over metal lath, which creates a drainage space between the building paper and the stucco, allowing water to drain out through the weep screed at the foundation (see Figure 1-29).

Stucco relies on this drainage plane for waterproofing, since the stucco material itself is relatively porous.

It tends to soak up water when it rains, but it dries out quickly since it is highly permeable to water vapor.

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Stucco-Wall Structure Requirements & Stucco Cracking

Portland-cement stucco shrinks as it dries, which normally creates small hairline cracks in the finished surface. Larger cracks may form, however, if there is significant movement in the structure, since stucco is nonstructural and relatively rigid.

A well-designed foundation and good-quality, dry framing lumber with adequate bracing will minimize this type of movement. On stucco jobs with no structural sheathing, still common in some western states, adequate bracing for racking strength and rigidity is particularly critical.

Cracking can also result from thin sections in the stucco finish. To avoid these problems, fur out or straighten any bowed or irregular walls before applying stucco.

Expansion Joints in Stucco Walls

Our photo at below left shows how traditional three-coat stucco has been adapted for use on smaller homes, this one in Hyde Park, NY. On a building with relatively small unbroken fields of stucco exterior wall, often no expansion joints were used.

But where stucco is applied over metal lath on wood framing, the Portland Cement Association recommends expansion joints every 10 feet, forming panels of no more than 150 square feet. Expansion joints are used in some other stucco installation methods as well. Our second photo (below-right) shows an insulating-board based Stucco-wall expansion joint on an elevator tower on the Vassar College campus, Poughkeepsie, NY.

Traditional stucco exterior, Hyde Park NY (C) Daniel Friedman Traditional stucco exterior, Hyde Park NY (C) Daniel Friedman

Expansion joints are particularly critical at joints between dissimilar materials, such as where wood framing meets masonry, or wherever excessive movement is expected, such as the band joist area between two stories.

Many residential projects are built without expansion joints, which can lead to cracking given the excessive movement associated with today’s lower quality framing materials.

Metal Lath Support for Stucco Walls

Expanded metal lath stucco (C) Daniel FriedmanStucco will bond directly to most masonry surfaces, but on sheathed walls the stucco requires metal lath to form a mechanical bond to the wall.

On residential projects, contractors use either expanded metal lath or “stucco netting,” a 17- or 18-gauge galvanized wire woven into a hexagonal mesh that looks like chicken wire.

Lath should always run perpendicular to the studs, and expanded metal lath must be installed with the correct side pointed up or the plaster will slip off when troweled on.

Our photo (left) shows exposed metal lath in the stucco exterior of a poorly-finished home in New York. It looks as if the top coat of stucco may have not been applied at all.

The expanded metal lath used to support stucco on building exteriors (or interiors as well) is nailed or stapled approximately every 6 inches at studs and other framing members.

Galvanized staples are now widely used to attach metal lath. However, unless the lath is the self-furring type, it should be installed with special furring nails that space the lath about 1/4-inch from the wall, fully embedding it in the scratch coat, according to stucco expert Ron Webber, of Procoat Systems, in Orange, California.

Expanded metal lath exposed (C) Daniel Friedman

Another common stucco lath problem, according to Webber, is that lath installed too tightly at corners causes poor embedment of the mesh at the corners.

This will cause cracks at the corners as the building undergoes normal movement with changes in temperature and humidity. To prevent corner cracks, installers should use a special corner bead called Cornerite™ or build up the corners with two layers of wire.

Another option is to pull the lath away from the building at the corners to make sure it is properly embedded.

The corners at either side of window and door headers is another common location for stucco cracks. To reinforce these areas and reduce cracking, some contractors add a second layer of reinforcing at these corners using a rectangular section of metal lath placed diagonally at each corner.

The metal lath should form a continuous layer around the building with all laps wired together and vertical laps staggered. With large-mesh reinforcement, lap vertical and horizontal joints at least one full mesh and a minimum of 2 inches. For small-mesh reinforcement, the laps should be at least 1 inch.

Stucco Recipes & Stucco Mixtures

Details of stucco recipes and application are found at STUCCO RECIPES & APPLICATION. Excerpts are below.

Stucco is a mixture of Portland cement, sand, and water, with a little lime or a plasticizer added for workability. A proper mixture has good tensile strength and weather resistance and the ability to bond well to the mesh or substrate. It is also easy to trowel on and resists sagging. In cold climates, it must also have freeze-thaw durability, usually obtained by using air-entrained plaster.

The cement base can be masonry cement, plastic cement, or Portland cement, which may have air-entraining additives. Do not add lime or a plasticizer to masonry cement or plastic cement since these already contain plasticizers. While approximate proportions are well established, the right mix for a job depends on the weather exposure of the wall and weather conditions during application (see Table 1-9).

Other than the right proportions, the keys to a good stucco mix are clean, good quality sand and clean potable water. Since sand makes up about 97% of the stucco mixture by volume, it is critical to use good sand. The sand should be free of vegetable matter, loam, clay, silt, and soluble salts and should conform to ASTM C897, which designates the distribution of particle sizes (gradation). Impurities in the sand or water can affect the strength of the mix, and poor grading of the sand will hurt its workability.

Salts can cause staining on the finished surface from efflorescence.

Stucco Wall Application Procedure

Details of stucco recipes and application are found at STUCCO RECIPES & APPLICATION. Excerpts are below.

Stucco can either be hand troweled or blown with a machine. Some stucco contractors use a pump for the base coats but apply the finish coat by hand.

Although the mixes are slightly different for the two approaches, both can produce a high-quality finish. In threecoat stucco, the first and second coats are 3/8-inch thick, and the finish coat is 1/8-inch for a total thickness of 7/8 to 1 inch.

Applying the Stucco First or Scratch Coat

The first, or “scratch,” coat, which forms the base for the next two coats, should completely encase the reinforcement. While still wet, the plaster is scored horizontally with a special metal rake or trowel to create a good mechanical bond with the second coat (vertical scratching promotes cracking at studs).

For proper curing, the scratch coat needs to be kept moist by misting or fogging with water for 48 hours. Except in very moist weather, misting should start as soon as the freshly applied stucco lightens in color and be repeated at the start and end of each day until the second coat goes on.

Applying the Stucco Wall Brown Coat

The second, or “brown,” coat should go on as soon as the first coat is hard enough to accept the second coat without cracking, but at least 48 hours later, according to the IRC. The second coat fills any cracks in the scratch coat, and the additional sand in the brown coat helps prevent new shrinkage cracks. Whether it is hand troweled or machine-applied, it must be leveled with a straightedge (“rodded”) and floated to produce an even surface for the final coat.

A short delay between the first and second coat helps to create a good bond between the two and strengthens the scratch coat by rewetting it for a more complete cure. Any cracks larger than 1 1/16-inch in the brown coat should be patched before the top coat goes on. In the Southwest, where adobe is popular, the brown coat is often steel troweled for an adobe look and serves as the final coat.

Applying the Stucco Wall Finish Coat

After the second coat is allowed to cure for a minimum of 7 days (14 will allow a more complete cure), the top coat is applied to provide the finish color and texture. Many contractors now use premixed color coats, some with acrylic additives to increase water resistance and flexibility.

Creating a uniform color and texture requires a skilled applicator, uniform mixing, favorable weather (avoid direct sun), and a uniform substrate without variations in texture or water absorption.

Problems in the substrate will tend to show through the thin finish coat. It is best to do an entire side of the building in one batch with no cold joints. A modest amount of color variation is considered part of the character of traditional stucco, but too much is a sign of substandard work.

A certain amount of shrinkage cracking is also inevitable in stucco exteriors. Application over wood-frame construction results in more cracking than over concrete block or other more stable substrates. Coarse textures in the finish will tend to hide the cracks better than smooth finishes. Even under the best of conditions, small shrinkage cracks of less than 1/16-inch will occur in the finished stucco and are to be expected. Generally these do not leak or indicate substandard work.

The Importance of Weather to Stucco Work and Stucco Paint Coatings

See details about the cause, diagnosis, cure, or prevention of paint failures on stucco exterior walls, discussed at STUCCO FAILURES DUE TO WEATHER.

EIFS Failure due to poor installation practices (C) Daniel FriedmanMoisture, humidity, rain, or wet conditions during thin-coat or EIFS stucco work can lead to a subsequent series of failures of the entire installation.

The home shown in our photo (left) was the subject of litigation. We observed that the final stucco had been applied over wet surfaces and in some cases over surfaces that also had been troubled by soil that had splashed-up on the building during rainy weather.

Stucco wall paint failures are also traced to moisture, efflorescence, and failure to adequately clean the exterior and then allow it to dry before painting.

See PAINT on STUCCO, FAILURES and also PAINTING in SUN or WIND.

  • Temperature during stucco work will speed up or slow down the hydration process that cures the cement in stucco. It is best to avoid application in extremely hot or cold temperatures. In hot, dry, and windy weather, frequent misting will be required on the scratch coat or the installer may need to tape polyethylene sheeting in place for proper curing.
  • Direct sun tends to dry out the fresh stucco too fast, so installers should try to follow the shade around the building. Also, retardants are available that can be sprayed on the scratch or brown coat in hot weather to slow down the curing. Sun, heat, and rapid drying conditions can present special stucco application troubles or subsequent stucco paint coating troubles in hot dry climates such as the American Southwest. (Photo at left).
  • Cold weather also presents problems. Stucco should not be applied under 40°F, and it should not be allowed to freeze within 24 hours of application. Accelerators can be added to the stucco mix in cold weather, but these can weaken the material, and calcium-based accelerators can lead to efflorescence. Heating the materials and, if necessary, tenting the structure can permit work to proceed in cold, even freezing, weather.
  • Cool, moist weather is ideal for traditional stucco wall installations. In humid weather, with relative humidity over 70% or heavy fog, misting is not usually required.

See STUCCO FAILURES DUE TO WEATHER.

More about stucco paint and coating failures is found at found at STUCCO PAINT FAILURES.

Thin-Coat Stucco Specifications

Details about thin-coat stucco applications are at STUCCO THIN COAT APPLICATION. Excerpts are below.

Thin coat stucco installation (C) Daniel FriedmanIn an effort to speed up stucco application time and simplify the process, several manufacturers have introduced proprietary thin-coat stucco systems variously referred to as one-coat, two-coat, thin-coat, or fiberglass-reinforced stucco.

Our photo of a thin-coat stucco wall being constructed (left) was at a Barnes and Noble bookstore in Poughkeepsie, NY.

All these systems apply a single base coat and a top coat with a total thickness of  2/8 to 1/2-inch, compared to  7/8 to 1 inch for traditional three-coat stucco. The thinner finish weighs from 5 to 6 pounds per square foot, compared to 9 pounds for three-coat, and it is cost-competitive with traditional stucco.

Like traditional three-coat stucco, thin-coat is applied over wire mesh or expanded metal lath by hand or pump. It is backed up by a waterproof drainage plane consisting of Grade D building paper, integral flashings, and a weep screed along the top of the foundation to drain away any trapped water.

Some manufacturers, such as United States Gypsum, have introduced hybrid systems in which the stucco is applied to a cementitious board rather than to wire mesh. The advantage is that cement board is impervious to moisture. The drainage plane, and in some cases a layer of foam insulation, lies behind the cement board.

Thin Coat Stucco Application Procedure

The base coat in thin-coat systems has acrylic polymers and chopped fiberglass added to increase its strength and resistance to shrinkage cracking and to freeze-thaw cycles.

The base coat is premixed with only sand and water added at the job site. Most contractors using these systems apply an elastomeric color coat, similar to a thick acrylic paint with fine aggregate, and formulated to bridge small gaps less than 1/16-inch.

This produces a smoother finish that is more water- and stain-resistant and less prone to cracking than a traditional stucco. The top coat can also be a traditional cement stucco finish.

Most of these systems require a 24- to 48-hour moist cure and a total of six or seven days of curing before the top coat is applied. Some require a primer for acrylic finishes.

Our thin-coat stucco wall damage photo (above-left) shows the vulnerability of this system to damage by common events at or around a building: in this case the use of a weed-whacker to trim growth close to the building wall. This EIFS installation is also installed so close to the ground as to invite insect attack on the structure.

Also see Insects & Foam Insulation.

Pros and Cons of Alternative Stucco Systems

To their credit, properly applied onecoat systems are more waterproof and less prone to shrinkage cracking than traditional stucco. It is easier to obtain a uniform color and texture with the synthetic color coat than with a traditional cementitious finish coat. Whether a customer prefers the uniform color of a synthetic finish or the more muted and variable color of cement stucco is a matter of taste.

Our photo of a leaky stucco window sill on a New York home (left) shows a damaged, leaky sill where plastic mesh was used as a modern substitute for expanded metal lath.

On the downside, one-coat systems are less impact resistant than traditional three-coat stucco. And with a thickness of only 3/8-inch, one-coat systems are less able to hide irregularities in the framing and are more likely to have thin spots that are prone to problems.

Also, one-coat stucco systems are not completely waterproof. Over time, water will find its way in at joints, penetrations, or cracks, and the synthetic stucco will be slower to dry out than the more permeable traditional stucco.

Finally, each system is proprietary and must be installed according to the manufacturer’s approved specs and details, which vary from system to system. Otherwise, warranties are voided and code approvals, which are based on building code evaluation reports, are invalid. For both reasons, contractors should avoid mixing and matching components from different thin-coat systems.

Details about thin-coat stucco applications are
at
STUCCO THIN COAT APPLICATION.

Exterior Insulation and Finish Systems (EIFS)

Details about EIFS wall problems, inspections, and litigation are found at our home page for this topic:
SIDING EIFS & STUCCO.

Photograph of EIFS synthetic stucco exterior (C) Daniel Friedman

When originally imported from Europe to the United States in the 1970s, most exterior insulation and finish systems (EIFS) were “barrier” type systems. They were designed to create a waterproof exterior skin consisting of a thin layer of acrylic polymer-based synthetic stucco directly applied to foam insulation.

Our photo (left) shows a modern Sto-Wall covered home that was investigated to diagnose the sources of wall leaks through the stucco system. We found many installation details that did not follow the manufacturer's recommendations. As a result there were significant leaks into building walls and a considerable mold contamination issue as well.

The expanded polystyrene (EPS) foam was glued to the building’s sheathing. A layer of fiberglass cloth embedded in the synthetic stucco provided reinforcement, and a thin acrylic finish coat added color and texture.


EIFS Leaks in a Sto Wall (C) Daniel Friedman

With the EPS glued directly to the sheathing, there was no place for building paper or conventional flashings at penetrations. Openings, joints, and penetrations relied on caulks and sealants for waterproofing. With no backup waterproofing or drainage layer, there was little margin for error.

While these systems performed adequately in Europe for nearly 25 years, the United States version had thinner base coats and lower polymer content, creating a weaker skin.

Also, workmanship in the United States was often inferior due to lack of applicator training and quality-control programs.

The water running down this building interior wall (photo above-left) was traced to omission of the manufacturer-specified sealant methods at the top of the building exterior wall. Wind-blown rain entered the wall top just below the soffit overhang, wet the wall interior cavity, and finally appeared on the foundation walls below.

When water leaked into these systems through failed caulk joints, cracks in the stucco skin, or through the window frames themselves, it wet the foam insulation, sheathing, and sometimes the structural framework.

A photo guide to some common leak points found on EIFS clad buildings is at SIDING EIFS WALL LEAK POINTS.

If you are an EIFS manufacturer, installer, or EIFS inspector, contact us at LINK EXCHANGE to add listings - there is no fee.

Details about EIFS wall problems, inspections, and litigation are found at SIDING EIFS & STUCCO.

Also see INSECTS & FOAM INSULATION

Drainage Systems for EIFS "Stucco" Walls to Reduce Leak Damage

Details about the role of drainage systems in preventing leaks and water damage to EIFS-clad buildings can be found at STUCCO EIFS DRAINAGE SYSTEMS. Excerpts are below.

Figure 1-30: EIFS Wall System Drainage (C) Wiley and Sons, S Bliss


In response to these problems, most EIFS manufacturers have introduced new “drainage” or “water-managed” systems, which require the same type of waterproof drainage plane found behind traditional stucco systems (see Figure 1-30)

[Click to enlarge any image]

As with traditional stucco, layered building paper or plastic housewrap protects the framing and sheathing, and all exterior openings and penetrations are flashed to conduct any water to the outside of the sheathing wrap.

Since window leakage was the single biggest contributor to EIFS failures, pan flashing is recommended at windows.

Rather than gluing the EPS foam to the sheathing, the new drainage EIFS typically use mechanical fasteners and are designed with a capillary break between the back of the EPS and the sheathing wrap to promote drainage.

Some EIFS contractors use special corrugated or wrinkled sheathing papers to create the drainage space, while others have vertical grooves cut into the back face of the foam insulation.

In all cases, the drainage plane leads to a perforated weep flashing at the foundation to drain away any trapped water.

Workmanship & EIFS Exterior Stucco Wall Success

The backup drainage layer, however, should not provide an excuse for sloppy workmanship on the exterior skin. The new kinds of EIFS should still be made as waterproof as possible, since any water that leaks past the skin may be slow to dry out. EIFS consultant Russell Kenney, who has worked with these systems for nearly 20 years, recommends exceeding the minimum specs required by EIFS manufacturers.

Kenney recommends a higher-density EPS foam with only 2% water absorption by volume instead of the 4% allowed by ASTM C584. In addition, Kenney recommends a heavier 6-ounce reinforcing mesh versus the typical 3-ounce cloth, as well as special high-impact mesh in high-traffic areas.

He also recommends a 3/32-inch base coat applied in two layers, with the first layer used to partially embed the fiberglass reinforcing and the second layer to fully cover and protect it.

These steps will significantly improve the impact resistance of EIFS, but it is still less durable than traditional stucco or thin-coat stucco.

See details about the cause, diagnosis, cure, or prevention of paint failures on stucco exterior walls, found at STUCCO PAINT FAILURES.

Apply Sealant to EIFS Base Coat

As with the original barrier EIFS, all penetrations require a high-quality elastomeric sealant. The sealant needs to be applied to the base coat since the finish coat tends to soften when wet, providing a poor substrate for sealant. For the caulk joints to last, they must be wide enough to tolerate the anticipated movement, typically 3/8 to 1/2-inch, and backed up by backer rod (see “Joint Design,” page 37 in Best Practices Guide to Residential Construction).

While control joints are generally not needed along the length of the wall—unless it exceeds 75 feet and is in direct sun—they are required between floors on multistory buildings. Silicone sealant is recommended at all joints for its longevity and flexibility in cold temperatures.

In theory at least, drainage EIFS should function the same as any other exterior cladding systems. Any water that manages to penetrate the outer skin should be stopped by the drainage layer and safely drained away.

However, given the low permeability of polymer-based coatings and the tendency of EPS foam to soak up and hold water, EIFS are best avoided in residential projects unless high-quality workmanship and regular maintenance of sealants can be assured.

Details about the role of drainage systems in preventing leaks and water damage to EIFS-clad buildings can be found at STUCCO EIFS DRAINAGE SYSTEMS.

Reader Question: Desirability of using the BASEX stucco coating system

4/21/2014 Shannon said:

Hello,
We have just had all of the stucco removed and new stucco applied on our home over the last several weeks. Our contractor has mentioned the stucco subcontractor recommends a basex flexible membrane be applied prior to our color coat. How beneficial is this as the cost is close to $5000. I am wondering what real benefits we will gain or what disadvantages we will experience if we do not go with this option. Many thanks, Shannon

The only added information I have is that this recommendation is an anti-fracture BASEX membrane to go in before the final coat of plaster is installed. This is like a thin wire mesh that will limit the amount of cracking and pealing of the final coat of plaster. Not sure if that help provide the needed details.

Reply:

Shannon,

Basex is a product of Merlex Stucco (merlex.com) who offer some helpful information about BASEX in stucco applications. BASEX is a "Polymer-modified base coat and anti-fracture membrane for smooth-troweled finishes" - so what does that mean?

Merlex BASEX is specifically designed for application over brown coat where smooth-troweled finishes are used (such as Santa Barbara Finish). When mesh is embedded in BASEX, cracking is reduced significantly, which allows for higher-quality smooth-troweled finishes. BASEX contains a high percentage of polymer for flexibility, microscopic fibers for crack-resistance, and proprietary additives for workability and working time. The product has suction to ensure good bond between the finish plaster and base coat. BASEX can also be used on rescrubs directly over structurally sound existing plaster, eliminating the need for sandblasting.

In sum, picture a combination of a patented coating compound (modified portland cement) that is applied over a mesh base that in turn has been secured to the building wall. The manufacturer says the system can be applied over a variety of surfaces, new and old "... over standard Portland cement brown coat, concrete masonry units, existing stucco, and brick. "

It's notable that if BASEX is applied without the mesh coating, the promise of reduced cracking is in my words - nullified.

Here is contact information for the company

Merlex - Orange County Stucco Manufacturer - Executive Office
2911 Orange-Olive Rd.
Orange, CA 92865
Phone: 714-637-1700
Website: www.merlex.com
Email: service@merlex.com

Parex Exterior Insulation and Finish Systems (EIFS) also make use of basecoat and other products to reduce cracking as do other manufacturers.

ParexUSA
4125 E. La Palma Avenue, Suite 250
Anaheim, California 92807
Tel: 7877-547-8822
Email: info@parex.com
Technical Support 800.226.2424
Email: technicalservice@parexusa.com

I wanted to add some citations on the prevention of stucco cracking, but first must emphasize that proper construction, surface preparation, and importantly, following the stucco system manufacturer's instructions are the key ingredients in a successful job. Most of the failures I see are due to installation that does not follow what are sometimes unrealistically demanding instructions.

Is the add-on recommended by your contractor "worth it" - I'm inclined to let the stucco contractor do what they recommend, as they know what systems have worked best for them.

Also remember to look carefully at your warranty terms. In my OPINION stucco failures such as chalking, cracking, or leaks that are due to poor installation will usually show up in the first year or so, though some leaks such as those in EIFS systems can be a bit hard to spot and can leak into a wall where a mold problem develops for some time before occupants notice the trouble.

In general, as Cheple (2000) point out, using polymer additives improves the flexibility of the stucco coating and thus should improve its crack resistance. N

Needless to say there are countless citations on stucco cracking and crack prevention. Here are some I recommend for readers who want to consult those who've conducted more expert research:

  • Arnold, Andrew Eric, Chia-Ming Uang, and Andre Filiatrault. "Cyclic behavior and repair of stucco and gypsum woodframe walls: Phase I." CUREE Publication No (2003).
  • Arnold, Andrew Eric, Chia-Ming Uang, and Andre Filiatrault. "Cyclic behavior and repair of stucco and gypsum sheathed woodframe walls: Phase I." SSRP (2002): 07.
  • Bern, D. L., and F. F. Grant. "High-Performance Cement Plaster (Stucco) Systems." AEI 2008: Building Integration Solutions (2008).
  • Cheple, Marilou, and Patrick H. Huelman. Literature review of exterior insulation finish systems and stucco finishes. Cold Climate Housing Program, University of Minnesota, 2000.
  • Lstiburek, Joseph William, P. Eng, and M. A. Westford. "Rainwater Management Performance of Newly Constructed Residential Building Enclosures During August and September." (2005).
  • Spagna, Francesco J., and Stephen S. Ruggiero. "Stucco Cladding-Lessons Learned from Problematic Facades." ASTM SPECIAL TECHNICAL PUBLICATION 1422 (2003): 214-230.
  • Suprenant, Bruce A. "Stuccoing over masonry." Aberdeen’s Magazine of Masonry Construction (1990):

 

Exterior Insulation and Finish Systems (EIFS) Resources & Suppliers

  • Dryvit Systems www.dryvit.com
  • Parex www.parex.com
  • Senergy www.senergyeifs.com
  • Sto Corp. www.stocorp.com

Construction Sealant (Caulks) Suppliers & Products

  • Chemrex www.chemrex.com

Polyurethanes and other high-performance sealants

  • DAP www.dap.com
  • Acrylic latex caulks
  • Dow Corning Sealants www.dowcorningsealants.com
  • Silicone sealants
  • GE Silicones www.gesilicones.com Silicone sealant
  • Geocel Corp www.geocelusa.com Acrylic latex, tripolymer, copolymer, Kraton, and clear sealants
  • Macklanburg-Duncan www.mdteam.com Acrylic latex sealants
  • OSI Sealants Inc www.osisealants.com Polyseamseal PVA-based caulk. Pro Series includes latex, polyurethane, and Kraton sealants.
  • www.phenoseal.com Phenoseal vinyl adhesive caulk
  • Red Devil www.reddevil.com Acrylic, silicone, and butyl sealants
  • Sashco Sealants www.sashco.com Big Stretch and Mor-Flexx water-based sealants, Lexel Kraton sealant
  • Sika Corp www.sikaconstruction.com Complete line of Sikaflex polyurethane-based sealants, butyl sealant
  • Tremco Inc. www.tremcosealants.com High-performance, architectural-grade sealants,
  • UGL www.ugl.com Acrylic latex caulks
  • White Lightning www.wlcaulk.com Tripolymer, butyl, polyurethane, silicone, elastomeric, and other high-performance sealants

-- Adapted with permission from Best Practices Guide to Residential Construction.

 

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