• Changes in the properties of building papers and water resistant barriers (WRB’s)
• Change from plywood sheathings to OSB sheathings
• Higher levels of thermal resistance
• Use of interior plastic vapor barriers
• Changes in the properties of stucco renderings

Photograph 1: Pennsylvania Stucco “Shack”—Eastern Pennsylvania is the stucco failure capital of the United States.  Note the manufactured stone veneer—or “lumpy” stucco on the front façade.
 
 

Photograph 2: Hardcoat Stucco—Three coats have been traditionally applied directly over a single layer of impregnated felt or asphalt saturated kraft paper.  Today, this results in a bond between the stucco rendering and the outer layer of the felt or paper compromising drainage.
 
 

Photograph 3: Manufactured Stone Veneer—Manufactured stone veneer claddings are very similar to hardcoat stucco and perform in a similar manner.  In a manufactured stone veneer the outer coat of stucco is replaced with a thin stone layer.
 
 
  Photograph 4: Hardcoat Stucco Failures—Note that the damage is in the field of the wall away from windows.
 
 

Photograph 5: Failure on Steroids—Note the plastic vapor barrier “accelerant” in this Vancouver, Canada building.  

Building paper manufacturing changes and the introduction of plastic building papers (also referred to as “building wraps” or “housewraps”) led to a change in the water management attributes of stucco renderings installed directly over these materials.  Older building papers were more “robust” than more recently manufactured products—they weighed more and had more cellulose content.  As a result when stuccos were applied directly over them a bond between the stucco and the building paper did not develop due to the dimensional instability of the cellulose.  The absence of a bond permitted a modest degree of drainage to occur between the building paper and the stucco.  With more recently manufactured building papers a bond develops between the building paper and the stucco—preventing drainage between the building paper and the stucco.  The bond between plastic building papers and stucco is even greater (Photograph 6).
 
 

Photograph 6: Hardcoat Stucco Bonding to Plastic Building Paper—A young, happy engineer, discovers that stucco does indeed bond to plastic building papers preventing drainage.  The engineer is my friend Chris Schumacher—may he remain this happy when he gets older.

 
The solution to the bonding problem is pretty straightforward—the use of a “bond break”—an additional layer of building paper between the stucco and the water management layer building paper (two layers of building paper).  The best bond break between building paper and stucco, is, you guessed it, another layer of building paper (Figure 1).  Similarly, a building paper bond break should be used between plastic building papers and stucco.  For reasons that are not quite understood3 plastic building papers do not make as good a bond break as paper building papers (Photograph 7).  The use of a second layer of building paper as a bond break is not ubiquitous—it should be.  Stucco, today, needs every edge it can get.
 
 

Figure 1: Two Layers of Building Paper—The two layers of building paper are significant in the performance of hardcoat stucco assemblies.  The outer layer of building paper acts as bond break between the stucco and the inner layer of building paper permitting modest drainage of water between the two layers.
 
 

Photograph 7: Building Paper Bond Break—Traditional building paper is an excellent bond break between traditional hardcoat stucco and plastic building papers.

 
Another attribute that changed was the water vapor transmission of the plastic building papers versus the traditional building papers (impregnated felts and asphalt saturated kraft paper) (Figure 2).  What is the big deal with the shape of the curves?  Well, it’s a “Goldilocks” thing—the materials should not be too vapor open or too vapor closed—but “just right.”  With materials that are too vapor open—too much moisture stored/ absorbed in the stucco layer can be driven inwards through the material under solar induced drive causing damage in the sheathing layer.  With materials that are too vapor closed—not enough moisture will be able to exit the sheathing layer and dry outwards during drying events.
 

 

Figure 2: Permeance of Water Resistive Barriers (WRB’s)—Debate rages within the building science community as to what the curves mean.  The old guy in me intuitively believes that the shape of the curve describing the traditional building papers (WRB’s) is “good.”  And that the curve describing the “high perm” WRB is “not so good” and the curve describing the “low perm” WRB is “better but not as good as” the curve describing traditional building papers.  I believe that if we could get a plastic building paper with a curve that mirrors the shape of the traditional building papers the product would “kick building science butt.”

 
The stucco problem seems to be worse with “high perm” plastic WRB’s than with “low perm” materials.  As the “dwell” time for moisture in the stucco and WRB layers goes up, inward vapor transmission also goes up with “high perm” plastic WRB’s.  The “low perm” plastic building papers appear to do a better job of “throttling” the inward vapor drive protecting the sheathing.
On to the plywood versus oriented strand board (OSB) change.  Folks, this is a big deal.  No matter how many times manufacturers say that OSB is just like plywood it just isn’t so.  Check out Figure 3 and the relative differences in water vapor transmission between plywood and OSB.  Plywood becomes vapor permeable as it becomes wet—OSB does not.  Did I mention that this is a big deal?  When plywood gets wet it dries a lot easier (and faster) than when OSB gets wet because it becomes vapor open.  Moisture also migrates laterally within a plywood sheet a lot easier than OSB.  The lateral movement and vapor openness when wet allows the plywood to more easily redistribute moisture than OSB.  This means that with OSB moisture becomes concentrated at OSB/building paper interfaces—whereas with plywood the moisture is released into the cavity as well as allowed to migrate laterally reducing concentrations and localized moisture stresses.
 

 

Figure 3: Permeance of Plywood vs OSB Sheathing—Note the “hockey stick” shape of the plywood curve.  Hockey is good—remember that and life will be good.  The upward rise allows the plywood to dry more readily than OSB when it gets wet.

 
One solution to this problem is also pretty straightforward—the use of a ventilated air gap between the stucco and the building paper/OSB sub-assembly.
The air gap does not have to be particularly big to be a big deal—3/8 inch (9 mm).  One method of getting the air gap is to use a drainage mat between two layers of building paper (Photograph 8).  The gap allows redistribution of the moisture in both the stucco and the OSB sheathing.  The gap also does something else—if it is wide enough it becomes a ventilated space making the “Goldilocks” vapor curve argument moot.  Once we have a ventilated space (with meaningful air movement) the permeability of the traditional building papers and plastic building papers almost does not matter.  Anything between the “low perm” and “high perm” materials can be shown to work.  In fact, an insulated semi-permeable sheathing does the best job of controlling inward vapor drives in all climate zones.
 

 

Photograph 8: Air Gap—The air gap does not have to be particularly big to be a big deal—3/8 inch (9 mm).  One method of getting the air gap is to use a drainage mat between two layers of building paper.  The gap allows redistribution of the moisture in both the stucco and the OSB sheathing.

 
Higher levels of thermal resistance also makes things more difficult for all claddings, not just stucco.  The more insulation—the lower the energy flow across the assembly.  Less energy, less drying.  In cold climates, and during cold periods, claddings operate at colder temperatures as insulation levels rise.  The colder the cladding, the higher the moisture content in the cladding since most claddings are hygroscopic—they pick up moisture based on relative humidity rather than based on vapor pressure.  Similarly, the same goes for sheathings.  Plywood and OSB sheathings increase in moisture content during heating periods as cavity insulation levels rise.
The solution to this problem is the same as the plywood/OSB solution—an air gap or insulated sheathing.  Back ventilate claddings.  It is a good idea to do this for all claddings, not just stucco.  How much of an air gap? It seems that 3/8 inch (9 mm) or greater works.
Now, to the plastic vapor barrier thing.  What can I say that I haven’t said about this earlier.  The interior plastic vapor barrier prevents inward drying during cooling periods.  Except in extreme heating climates plastic vapor barriers are unnecessary.  The reduction of inward drying is often enough to push the wall over the edge if it is borderline to begin with (go back and look at Photograph 5). 
The solution to the plastic vapor barrier problem is also straightforward—don’t use one.  Use vapor retarders, not vapor barriers.  Better still don’t use either a vapor barrier or a vapor retarder.  Use insulating sheathings over drainage layers installed outward of framing.
The final “minor” change to consider is the stucco rendering itself.  Older stuccos had more lime in the mix and therefore were more vapor permeable.  This was a good thing as it allowed the stucco and the building paper and sheathing all to dry more readily to the exterior.  Today’s “new” stuccos are marvels of materials science.  Well, some of them.  Others are just kind of mixed up like moonshine and reflect the applicators favorite mix.  They have magic potions and pixie dust added to them making them a witches brew.  We have soaps, we have ammonia, we have latex, we have silica, we have who knows what.  What we do know is that some of these stuccos don’t breathe (aren’t vapor permeable) at all.  And this is not good.  Give me a good old fashioned brew—I mean mix- any day.  Ok, I will live with a little bit of polymer to give me some tensile strength, but not too much OK.  Breathing is a big deal.
So lets put all of these minor things together—the plastic housewrap, the OSB sheathing instead of plywood, the higher level of cavity insulation, the use of plastic vapor barriers and finally the use of low perm stucco and I give you the perfect storm—I give you Vancouver, Canada—the stucco failure capital of the world.
Take away the plastic vapor barrier and I give you—eastern Pennsylvania—the stucco failure capital of the United States.
So how to avoid all of this?  Easy.  Give me an air gap between the stucco and the building paper and get rid of the plastic vapor barrier.  We need to keep the OSB—the days of sheathing buildings with plywood are gone forever.  And we need to keep the high levels of cavity insulation for obvious reasons.  Another way to avoid all of these problems and to produce an energy efficient enclosure (that’s green, remember) is to use an insulating stucco—yes, you guessed it, a water-managed exterior insulation finish system (EIFS), where a layer of foam is installed between the drainage layer and the stucco creating a drainage space4—and without an interior vapor barrier.
 

Footnotes

• A partially virulent form is called Gehry-itus—fortunately this particular strain has only caused serious damage in Massachusetts and appears to have been contained to one building on the MIT campus.
• They get enough grief from me as it is, and it appears from almost everyone one else as well.  In their defense I point out that today’s windows perform better than windows manufactured 10, 25 and 50 years ago.  Not all water related problems can be blamed on windows—since they are demonstrably better and getting better all the time.
• Not understood by me—others probably have an explanation that I would be interested in getting—I am offering a modest reward—mostly to see if anyone actually reads these footnotes.
• The irony is rich and deep here since EIFS, the face-sealed kind, was fingered by many as the cause of major stucco failures in the early 1990’s and hardcoat stucco was held up at the time to be the cladding of choice, whereas today water-managed EIFS is the obvious answer to the current rash of hardcoat stucco failures.

Missing Kick Out flashing is a big red flag as we very often discover significant damage to stucco, sheathing, and framing in these locations.
 
One of the biggest potential leak areas on any house is where the eave overhang meets a vertical wall.  In this area, where the stucco wall continues past the bottom edge of the roofline, Kick Out Flashing must be installed where the first few courses of roofing abut the stucco.  This flashing is required to divert water run-off from roof into the gutter and keep water from getting behind the stucco at the bottom edge of the roof-wall interface.

 



To keep it simple, Kick Out Flashing needs to be installed wherever the end of a gutter runs into a wall.





This picture (above) is after all the stucco was removed from a chimney.  The sheathing was completely rotted. All this damage could have been prevented by Kick Outs. Below is an after shot of this same chimney with the new stucco and Kick Out installed.





 
Gutter Guards, Gutter Helmets, etc are absolutely not substitutes for Kick Out Flashing.  In fact, these gutter protectors actually increase water run off onto the walls and exacerbate the problem.





Is your Kick Out Flashing functioning? These are not:

Setting the Record Straight onStucco Refinishing

Note: The name of the community (“Maple Hill”) and resident (“Mr. Rogers”) were changed before posting for privacy. This is a copy of Ai Restoration’s response that was sent to all residents of “Maple Hill.”


Ai Restoration was contracted by a homeowner at Maple Hill to perform the needed restoration work to their stucco this spring. They received a letter with an attached article which has been circulating around Maple Hill and asked us to review it. The letter was written by a homeowner at Maple Hill, Mr. Rogers and was an honest summary of the article “Refinishing Stucco” hosted on the Bob Villa web site. Overall the article is inaccurate and misleading. The author of “Refinishing Stucco”, Maureen Blaney Flietner, is a freelance writer, not someone with industry experience. Ai Restoration took the time to respond to these inaccuracies. We hope you find our included written response informative.


Ai Restoration would like to thank Mr. Rogers for taking a closer look at some of the options available to rehabilitate Maple Hill’s stucco. The amount of information available is daunting and sifting through it all can become overwhelming and confusing. After reading “Refinishing Stucco” by Maureen Blaney Flietner and hosted on the Bob Villa web site, it became apparent that Ai had to respond to Mr. Rogers’ letter and this article. Some statements within the article are incorrect and overall the article is misleading. Despite gross inaccuracies, the article does serve to get the ball rolling on some pivotal concerns.

Stucco has been around for over three millennia. The actual stucco material itself is very basic, but problems that stem from it can become very complex when combined with today’s building systems. The application of traditional stucco has failed to stay current with other changes in construction, resulting in numerous problems that have only recently surfaced.

Recent changes in building procedures have resulted in decreased stucco system longevity. The past few decades of new home construction have put an incredible emphasis on maximizing energy efficiency within a home. As a result of this emphasis, many building materials were changed. How these new materials would interact with water was not sufficiently understood. Unfortunately, it has taken years to discover how a traditional stucco system would need to be altered to cope with water’s interaction within the new framework materials. Some important changes and additions to traditional, or hard-coat, stucco systems are: control joints, window flashing, stucco stop, weep screeds, drain fields, diverters, kick-outs, flexible joints at dissimilar surfaces, among others. Most of these important new features of a stucco system, such as weep screeds, are not present in Maple Hill. Trying to repair a dated, failing stucco system with more stucco is not a solution.

Patchwork repairs often produce less than appealing aesthetic results, while further weakening the system by adding unprotected cold joints. Color matching stucco is not as accurate as one would expect. Generally, the older the stucco is, the harder it is to match. The stucco at Maple Hill originated from manufactured premixed bags. If this same premix is put on top of the existing weathered stucco, obtaining an exact color match will be extremely difficult and repairs will be visible. Another concern is how well the texture can be matched. There are 30 primary stucco texture styles with endless variations of each. If the texture style is off, repairs will again be noticeable. Visible repairs of this nature often leave homeowners dissatisfied, decrease home values, and jeopardize the association’s ultimate approval. Finally, when stucco is patched, cold joints are formed. Encompassing the entire perimeter of the repair, a cold joint is the intersection of the new stucco with the existing stucco. The stucco bond is weakest at this joint. If left untreated, the majority of the cold joints will crack. When stucco repairs are made they should be protected and visually blended in with a good, waterproof elastomeric coating. A clear sealer should not be used in place of a coating.

For a damaged stucco system, the level of repair required for proper installation of a clear sealer, without sacrificing looks and performance, is immense and costly. These sealers penetrate into the stucco and fill the pores. Shortly after they are applied, water will literally bead off the stucco like a newly waxed car. Although clear sealers are a substantial part of our company’s repertoire, Ai does not recommend them for a failing stucco system. The stucco must be in excellent condition for a clear sealer to be effective. Sealers are designed for preservation, not restoration.

The biggest downside to clear sealers is their inability to repair or prevent cracks within the stucco. A clear sealer cannot bridge, or fill, cracks. Sealing a stucco system with cracks present will defeat the purpose of the sealer, because water will simply penetrate through the cracks. It will also increase the amount of water running down the surface of the wall and force more water through any existing cracks. If the cracks are repaired with any type of cementious material, like more stucco, they will simply crack again. Cracks must be filled with a specialized flexible material. Although this is an excellent mechanical fix, the filled cracks will not blend in satisfactorily, unless the building is coated. Any other repairs made to the stucco will not be hidden or color corrected if simply clear sealed. Additionally, sealed stucco cannot guard against future cracking like coated stucco does. Clear sealers applied to failing stucco are an ineffective waste of money.

Even though clear sealers are not suitable for the majority of Maple Hill, waterproofing your home is still the most fundamental objective. The majority of all stucco problems originate from, and are amplified by, water. The most significant of these problems arise when water penetrates beyond the stucco system and comes in prolonged contact with the framing system. As with the majority of traditional stucco installed before the turn of the century, Maple Hill’s stucco is not capable of managing water penetration through the stucco system. Problems resulting from system breaches include, but are not limited to: delamination and cracking of the stucco, rot and structural damage, mold and mildew, insect infestation, and structural failures. These water infiltration problems commonly originate from cracks within the stucco, but are also often traced to failures of roofing and flashing, window and door joints, and other dissimilar surfaces to the stucco.

Coating applicators must have extensive knowledge of not only the complete stucco system, but also all parts of a building that contribute to, or are impacted by, any changes made to the stucco. Furthermore, the dynamics of moisture movement as related to these systems must also be understood and provided for. Only after leaks are remedied and detail work is completed should a coating be installed. Painters moonlighting as stucco restoration contractors usually lack this competence and frequently compound the exact same problems they were hired to alleviate. In addition to these painters, the general public has not been equipped to recognize faults in product selection and/or application. Without the knowledge to see otherwise, the “paint” becomes the scapegoat when a failure occurs. Ai fully believes that the professional application of the proper stucco coating will decrease the potential for damage caused by the infiltration of water through stucco.

The largest misconception of all is the breathability of stucco and how it is effected by a coating. Slanted and uniformed sources champion stucco’s natural breathability, but putting a positive emphasis on this affinity for water is counterproductive. After the building phase, when stucco is fully cured, it does not require water for any reason. Hard-coat stucco absorbs, channels, and sheds water in great quantities. There is not one single benefit to wet stucco. When combined with even the tiniest faults in construction, which are increasingly rampant, water becomes severely destructive. Why encourage or even tolerate something that is unnecessary and destructive? Traditional stucco’s affinity for water acts only as a vehicle for damage. Once water is eliminated from stucco its associated problems wash away.

Four Classes of Vapor Permeance	Impermeable	0.1 perm or less
Examples:	glass, aluminum foil, and sheet metal
Semi-Impermeable	1.0 perms or less and greater than 0.1 perm
Examples:	oil-based paints and vinyl wallpaper
Semi-Permeable	10 perms or less and greater than 1.0 perms
Examples:	plywood and latex paints
Permeable	Greater than 10 perms
Examples:	house wrap, cellulose insulation and drywall
Table data attributed to Joseph Lstiburek of Building Science Corporation

Water, when in vapor form, must also be examined. Buildings are designed to allow the passage of water vapor between the interior and exterior walls. Permeability, or permeance (perms) is a measure of a substance’s ability to diffuse water molecules. Think of permeance as how much something can breathe. The higher the perm rating, the more breathable a substance is. All substances fall into one of four vapor permeance categories. The chart to the right explains the vapor permeance categories. The permeability of building materials controls a structure’s natural respiration.

When considering vapor transmission between the exterior and interior walls, the high breathability of stucco, (predominantly composed of Portland cement), plays less of a role than most think. To help explain why this is, please download the Vapor Permeance Chart PDF provided by the Building Science Corporation (BSC). Since the data in this chart contradicts claims made in “Refinishing Stucco,” it is important to examine the source. Building Science Corporation is composed of internationally recognized experts on moisture dynamics as related to building technology. Members of this corporation are closely involved in researching and developing national and international building standards and testing procedures (ASTM, ASHRAE). They are not contractors or manufacturers pushing products or a collection of freelance writers, photographers, and hobby farmers from Wisconsin, (see Maureen Blaney Flietner, author of “Refinishing Stucco.”) BSC’s chart defines “Traditional three-coat hard-coat stucco over building paper and OSB or plywood sheathing,” the same system present in Maple Hill, as ranging from “less than 1.0 perm and greater than 0.1 perm.” The net result is that highly permeable stucco becomes semi-impermeable when installed as a complete system. With respect to vapor transmission, the specific permeance of actual stucco is utterly irrelevant.

The strong effect of climate on stucco systems does not allow for stucco to be generalized on a national basis, though it often is. Temperature, humidity, and pressure differences between the interior and exterior of a building have significant effects on vapor transmission. Avoiding technical explanation, a quick example can be made of a home in the Miami heat that will have air conditioning running year round. The air conditioner reduces the humidity by removing moisture from the home’s interior air. As the humidity differences between the inside and outside of the home diverge, water vapor is literally sucked into a home from outside. This process is also experienced in PA. As the climate changes throughout the nation, temperature, humidity, and pressure vary, resulting in changes in vapor transmission. There are many elements in the codes for application of stucco that differ from region to region specifically to cope with dissimilar climates. For this reason, what’s best for stucco in Utah does not simply apply to other regions.

Aside from regional deviations, the term “paint” requires further definition. When describing a coating for stucco, “paint” is too general. As with all products, not everything performs the same. In fact, Ai uses quite a few different materials depending upon specific factors for each job. A high-build, elastomeric, waterproof coating is best suited for the majority of units within Maple Hill. This acrylic coating’s attributes are: over 300% elongation, flexibility retention at low temperatures, excellent wind driven rain protection, breathable (10 perms), resists color fading, high resistance to dirt pick up and staining, recoatable, and environmentally friendly. Paints with low perm ratings applied to stucco will eventually bubble and peel. This is likely to be one of the primary reasons for the coating failure on the Maple Hill home mentioned in Mr. Rogers’ letter. A good product balances the ability to guard against water infiltration while simultaneously allowing the building to transmit vapor. In over ten years of business, Ai has never had an elastomeric coating failure.

As many homeowners have found out already, Maple Hill’s stucco will not last a lifetime. Stucco, coated or not, requires maintenance for longevity and performance. Many believe that traditional stucco is maintenance free. That is completely false. It is understandable that there are concerns about “starting a maintenance cycle,” when one had not existed previously. Regardless of how residents address their stucco issues, the stucco must be sustained, or else the cycle of failures will absolutely continue. An elastomeric coating is easy and cost effective to maintain. About ten years after the waterproof acrylic is first applied, it will simply require a light cleaning and another top coat of material. No other solution will give such low maintenance costs and very minimally evasive work.

As expressed during our presentation last year, please feel free to call, email, or write with any questions or concerns you may have. Please understand that Ai Restoration does all forms of stucco restoration. If a mason is asked how to alleviate problems in Maple Hill, he will say “More Stucco” or “New Stucco.” Conversely, a painter will say, “Paint it!” Ai makes determinations on a wall-by-wall basis. We are equipped to do all repairs pertaining to the stucco system and our technicians posses excellent knowledge beyond it. We are not a one-dimensional company trying to push a single product or application. Based on our inspections and knowledge of the Maple Hill stucco systems, our proposition of a high-build elastomeric coating and included detail work is without question the best option. It is the longest lasting and most cost effective solution available. When all the facts and options are laid out, there is no close second.

Friday, March 20, 2009 3 - 8PM
Saturday, March 21, 2009 10AM - 4PM
Sunday, March 22, 2009 10AM - 4PM

@ Delaware Valley College, Route 202 South, Doylestown, PA

• Beautiful landscape, room and window box displays on view
• Over 60 exhibitors featuring the latest products and services for the garden and home
• Free workshops with tips and techniques for gardening and home projects
• Free children’s programs

Bucks Beautiful
Delaware Valley College