Some Background About Stucco-and Problems

By Mark J. Reinmiller, P.E. 12/19/2013 There is a not so little secret going around about stucco and manufactured stone (also known as cast stone or cultured stone-throughout this article when I refer to stucco almost everything written also applies to manufactured stone). I should also mention that this article pertains to masonry stucco installed on wood-framed walls with wall sheathing (I’ll describe types of stucco and wall construction later).

While much of what is written in this article can apply to stucco of any age, much of what is written pertains to stucco installations from approximately the mid to late 1980s to present.   Back to the not so little secret-it can be a problem-a big problem. Think leaks, and damage-lots of damage. Rain water manages to find its way through the stucco and into the walls behind the stucco.  Below Laundry Room Window-1More often than not, the water does not get all the way to the inside of the building. It usually gets trapped between the stucco and the face of the wall sheathing. Because the leakage (professionals usually say water penetration) is not obvious, the water can do a lot of bad things before you realize what is happening.

And then there is denial. If you can’t see it, it must not be happening. Because who wants to spend the price ranging from a high end luxury car to an exotic foreign sports car to have the pleasure of going through many months of having your house torn apart and put back together so that it can look about exactly the same as it was before you started? And, hopefully it won’t leak when the process is completed (I won’t mention that that is not a sure thing.)

OLYMPUS DIGITAL CAMERA Now you may be saying that you see houses that are 25 or 50 years old, and even older than have stucco and they seem to be just fine. Or, you may also be saying that I don’t have a problem because my house does not have Dryvit, or synthetic stucco, or Exterior Insulation Finish System (often called EIFS). Not so fast. Houses with stucco that were built in about the mid-1980s or earlier often do not have big problems. Methods and materials of construction change. Sometimes a handful of small or not so small changes cause unintended consequences, like water penetration and lawsuits.

First, I should clarify a few things-Stucco can be installed over masonry (i.e. brick, concrete block, stone). That type of construction is not included in this article. Dryvit, or synthetic stucco, or EIFS is also a different material. These material are acrylic-based materials that are installed over foam insulation board. There have been well-publicized problems with EIFS due to water penetration and damage.


Although the problems with EIFS are often quite similar to that of masonry stucco, the two materials are quite different and EIFS is also not included in this article. To further clarify or confuse you, I should mention that acrylic-based finished coatings are often used with masonry stucco, but that does not make the installation an EIFS.  Also, a typical masonry stucco installation is a three-coat system. There are many proprietary systems that combine the first two coats (the scratch coat and brown coat) into one. These are referred to an one-coat systems, even though they still have a finish coat, and therefore in reality are two-coat systems. These are sometimes referred to as synthetic stucco systems, but they again have nothing to do with EIFS.    

Before I can ahead of myself, I should explain whatDSCN1338   traditional stucco, or masonry stucco or plaster, or hard coat stucco is.  Stucco in modern times is a cement based product like concrete, with some differences. A thin layer of concrete would not stick very well to most walls and would fall off over time. So for houses or building constructed with wood-framed walls, to put concrete on the walls we have to do some things different. 



Concrete and virtually all masonry products are somewhat porous. Water passes through them, which is not a desirable characteristic for a wall surface. To deal with this problem we need something behind the stucco to keep the water out of the walls. This something in the past was typically tar paper (technically known as builders felt) or another material which serves the same purpose (i.e. Grade D building paper). These are felt or paper based materials that are coated with asphalt, which is good at repelling water. Wait a minute. Something does not sound right here. You put a porous material on the walls and then put a waterproof (actually water-resistant) material behind it? Well, yes. Because if we put the tar paper on the outside your house would have all the charm of a chicken coup. Whereas when we put the stucco on the outside we can have the look of a stately mansion, or at least something presentable. And the stucco is supposed to protect the tar paper. A few more things are involved in getting the stucco to stick on the walls and look presentable. The sticking part is very important.  DSC_0352 Since the tar paper cannot hold the stucco to the walls we install something that can-lath. In some old houses lath can consist of thin wood strips, but we are going to skip that option. Typically, lath is a type of wire mesh that is nailed to the walls to hold the stucco. There are several types-woven wire mesh, sometimes called stucco netting, looks similar to chicken wire. Welded wire mesh consists of wire welded together in a rectangular grid pattern. Expanded metal lath, sometimes called diamond lath is made from a sheet of metal that is slit at regular spacing and then stretched out to create diamond shaped openings. Lath used on exterior walls is typically galvanized to protect the steel from corroding.

To get the stucco to stick to the lath and to provide additional corrosion protection we want encase the lath completely in the stucco. That can sometimes be accomplished by forcing the stucco behind lath that is not tightly nailed to the face of the wall. The preferable approach is to space, or fur, the lath away from the wall surface. This used to be done using self-furring nails, which are nails that have a spacer placed between the wall and the lath. Nowadays, self-furring lath is typically used. Self-furring lath is manufactured with dimples or ridges that space the lath away from the wall. Now we can finally put the stucco on the walls.

Traditional masonry stucco is typically approximately 7/8” thick. But we cannot just slap a 7/8” thick layer of concrete on the walls, so we typically put it on in three layers, which is why it is sometimes called three-coat stucco.   


 The first layer, called the scratch coat, is approximately 3/8” thick and is used to embed the lath and form a good base for the next layer.    Its called the scratch coat because approximately 1/8” deep horizontal grooves are scored into this layer to improve the bond of the next layer-the brown coat. The brown coat is also approximately 3/8” thick and is the about the same composition as the base coat, except it typically has a little higher ratio of sand to cement. The brown coat builds up the thickness of the concrete and allows for leveling-hopefully to provide a relatively flat and even surface. The final coat-the finish coat, is typically approximately 1/8” thick and is often pigmented to provide the color to the walls. This layer can be applied with a relatively smooth finish or one of many different textures or patterns. We are now done.

Not so fast!. We still have to deal with a few more things. Remember the leaks. While all masonry products are porous, the amount of porosity varies with a number of factors. Well-proportioned and properly installed stucco can have a relatively low porosity. All cement-based products shrink and usually crack. The amount of cracking that occurs and the significance of the cracking also varies with a number of factors. The primary factors are the ratio of sand to cement, the ratio of water to cement, the characteristics of the sand, and the rate at which the stucco dries.


That may sounds complicated, and it is.   To properly apply stucco and end up with a good product takes experience and knowledge, something that has usually been lacking in recent years.

In addition to the water that can pass through the stucco itself, there are bigger problems with water that can get past the stucco. There are many things that go along with building a house that create gaps or joints in the walls. These gaps and joints are usually the biggest problem. Water can easily enter small openings, but it cannot easily leave by these opening. Gaps and joints should typically be covered or sealed with flashings or sealants. Flashings are typically metal or plastic materials that shield joints or openings from water or provide a way for water to drain out of a wall. Sealants, or caulks are used to fill joints or openings. In many cases these components are not installed properly-or installed at all. Water that passes through the stucco should be stopped by the WRB and then drain out of the wall.


And here is where our problems start to magnify. The WRB and the lath are attached with nails or staples, which create thousands of tiny holes in the WRB. This can also some water to pass through the WRB. The WRB also must be installed or sealed at holes and joints so that water penetration cannot occur. If this is not done properly a lot of water will get behind the WRB. Once the water gets behind the WRB those big problems can begin. You may end up with obvious or not so obvious leaks into the house. Regardless of whether you see water, you can be assured that some water is getting into the walls.

After passing the WRB the next layer is the wall sheathing. In relatively old house this usually consisted of wood boards. From about the end of WWII or later until about the mid-1970s plywood was often used for wall sheathing. Other wood or fiber composition boards and gypsum materials were also used as wall sheathing, but in this article I am going to focus on wood, plywood, and “OSB” wall sheathing. “OSB” stands for Oriented Strand Board.  OLYMPUS DIGITAL CAMERA  That’s a fancy name for a material that is composed of strands of wood oriented in layers and directions and glued together to produce a thin panel that behaves similar to plywood. There are some big differences in these difference wall sheathing materials. The 1970s. You remember, Bell bottom, big hair, Disco. Well yes, but I was thinking lines at gas stations and running out of oil. As it was getting more expensive to heat our houses there was a push to increase energy efficiency. Some rocket scientists and others got together and figured out that we built houses without much insulation and with enough air leaks to well-blow the moisture out of the walls. I am simplifying things a little, but some of the water that got into our walls from outside and some of the moisture that got into our walls from the inside (that’s a story for another article) got carried away by airflow in the walls. Increasing the insulation in the walls and reducing air leaks in walls reduces airflow-airflow that used to dry out wall cavities.

Back to wall sheathing.    Many houses with wood and plywood wall sheathing have walls with relatively little insulation and a lot of air leaks.


When there is not excessive water penetration into the walls these walls can usually handle the water by carrying it away with the airflow. Wood and plywood can also be fairly tolerant of water. Over the years the amount of insulation in walls has increased and most builders do a better at reducing air leaks. In about the mid-1980s  the use of “OSB” sheathing increase significantly because of its cost advantage over plywood. From a structural standpoint OSB and plywood perform about the same. However, it turns out that OSB and plywood have some significant differences. OSB dries much slower than plywood and OSB deteriorates (i.e. rots) much faster than plywood. That’s not a good thing when you have water in your walls.

We have learned some other things that have caused problems with stucco. There have been changes in the weight and construction of tar paper and other products have come along for use instead of tar paper.

One of these is Tyvek (yea, the envelopes you cannot tear). For reasons that are not completely clear (at least to me), it seems that stucco may like to stick to the newer builders felt or Grade D paper than it used to. Also, it is thought that stucco affect a desirable characteristic of Tyvek-its ability to repel moisture. These functions are important characteristic of a WRB. You want a small gap between the stucco and the WRB to allow water to drain down and out of the walls (more on that later). And, of course you want the WRB to repel water.

So to quickly summarize what I’ve spent many words explaining, with modern stucco often a lot of water gets in, it can’t get out, and it rots the walls away. Not to mention mold (possibly deadly, toxic, lethal MOLD-just kidding!-maybe.). So now what do we do? Well, first we try to find out if we have a problem, and how bad that problem may be. Then, if we are lucky, we find someone to sue! Well, maybe not. But we have to figure out how to deal with the unfortunate situation. By visually looking at the outside and inside of the house (in places you may never think to look) an experienced professional can often find some signs of past water penetration that you did not know about and can determine whether the details regarding the stucco installation are such that water penetration would likely occur. This and the increasing knowledge regarding problems with modern stucco is whether the ball usually starts rolling. Moisture consultants, stucco inspectors or building scientists usually come next. These are usually people you never heard of that come out to give you more bad news (well, its not always bad news). A consultant will usually perform a visual inspection to look at the details of installation and to look for signs of past water penetration, and then will conduct moisture testing. Unfortunately, because water likes to hide inside of walls finding it is not necessarily easy.

The common method of checking for moisture in the walls is to drill approximately small holes in the exterior or interior walls below windows and many other areas where water penetration may occur.

A moisture meter with metal probes is then used to measure the moisture level in the wall sheathing.

Readings higher than 16% raise eyebrows and readings higher than 19% are frowned upon.

When drilling holes in the exterior walls the goal it to drill through the stucco, but not the wall sheathing. When the pointed probes are pushed into the wall sheathing you want the consultant to have to push hard. If not, there is a reasonably good chance the wall sheathing is rotted. But what if it has not rained for awhile? That’s where things get a bit tricky. Because the water likes to hang out in the walls the wall sheathing can stay wet for along time after it has rained.


And although the time since it last rained, the amount of rain, and the direction of the rain will affect the results, experience shows that there can still be relative differences in the moisture readings between areas that have gotten wet and areas that have not. The differences can vary significantly at different sides of the house because the wind affects how much water actually hits the walls.

In recent years thermal imaging cameras or infrared cameras how come down in price and many inspectors have begun using these to detect moisture in walls, missing insulation, abnormal psychic energy and many other things (just kidding about the abnormal psychic energy-I think). The problem with using infrared cameras to detect moisture in walls is that they only work under certain weather conditions, they can find water penetration that has not occurred, and they may not find water penetration that has occurred. I believe most reputable and experienced consultants will concur that infrared cameras have a place in moisture consulting, but by themselves are very unreliable. If they were reliable, do you think consultants would really enjoy drilling dozens of holes in your walls to take readings and then have to patch the walls? If the testing indicates that there is a possible problem, what happens next?

That depends. If you own the house and are not planning on selling anytime soon you may go the denial route.  OLYMPUS DIGITAL CAMERA  This may work for awhile, but may not turn out so well. If word gets out that there is a problem in the neighborhood and if others start having the stucco ripped off of the walls, you may find it hard to sell the house in the future, not to mention the obligation to disclose knowledge of a possible problem. You may also end up with far more damage than if you dealt with the problem earlier. Most of us in the business have seen houses where wall sheathing and wall framing is completely deteriorated at large areas and the inside of those walls have looked just fine. And then there is the issue of lawsuits (more on that latter). Before tearing off the stucco or throwing a large sum of money at a potential buyer, it would be wise to do a little more investigating.

Ok, you have looked all over my house and drilled dozens of holes in the walls, what now? Well, some of us like to make some bigger holes in exterior or interior walls to further examine conditions. Some of us have other techniques to look for damage using probes or a video camera with a small camera attached to a long flexible wand. This further evaluation serves a couple of useful purposes. It can verify that the results of the moisture testing were accurate and determine whether there is significant damage. It can also provide additional evidence as to why the water penetration occurred. This may be very helpful. If the testing shows that there has been significant water penetration and that damage has occurred, the best approach is to deal with the situation relatively soon. That may not be next week or next month, but it probably should be before next year.

If you thought that what has happened so far has been disruptive, you have not seen anything yet. Think scaffolding completely surrounding the house, covering or protecting or moving landscaping and air conditioning units, possibly tearing out patios, steps, decks, many workers tearing the stucco off of the walls, covering and removing plastic from the walls several times, installing various layers of WRB, flashings, accessories, etc. and then installing at least two or hopefully three layers of stucco on the walls. And, there is a good chance that you may need to replace the windows. Oh, and hopefully putting everything else back to the way it was. And, you better make sure that the contractor or contractors that perform this work are knowledgeable and experienced. It is also advisable to have an independent consultant inspect the work at key stages to increase the chance that the new work will turn out far better than the original work.

Lastly, I’ll mention lawsuits.    You see, while many factors were involved in creating the problems, typically the problems occurred because the builder or contractor did not follow typical industry standards or codes.


And even if you are past the warranty period, possibly by many years, it may still be possible to recover money for at least part of your expenses. The conditions and timing regarding claims or lawsuits get very complicated, and I am certainty not qualified to discuss the subject much further. In general, there are typically various Statutes of limitation that can affect your ability to file a lawsuit, and there is usually, if not always, a Statute of repose that limits the time you have file a lawsuit, no matter how good a case you may have. So if you have any thoughts of recovering some money, it would be wise to consult an attorney as soon as possible.

If you find yourself up late at night reading about the horrors of stucco, you will come across some terms and acronyms that you never heard of or thought you would care about. Weep screeds and kick-out flashing; casing or stop beads expansion joints, backer rod, etc. come to mind.   OLYMPUS DIGITAL CAMERAThis article is not intended to make anyone an expert on stucco, but perhaps a brief explanation would be helpful.

Weep screeds are a type of flashing installed at the bottom of a wall to allow water to drain out from behind the stucco. Kick-out flashing are used at the junction of walls and the side edges of shingles roofs. This flashing directs water away from the wall so that it does not drain behind the stucco. Kick-out flashing is not typically referenced by name in most codes and standards. However, most codes and standards have specific wording requiring the installation of flashing to keep water out from behind the stucco. Backer rod is a flexible, compressible rope like material typically made from polyethylene foam. It is used to fill relatively large gaps before sealing the gaps with caulk. Relatively wide joints are typically needed when sealants are subject to expansion and contraction. Otherwise, the sealant is likely to fail. Also, gaps are needed between dissimilar materials to minimize cracking that can occur as a result of expansion/contraction. Expansion joints are also required by typical building codes or standards to minimize cracking that can occur as a result of expansion/contraction.


And then there are building codes like the International Residential Code (IRC) or your state’s equivalent, the International Building Code (IBC) for non-residential and multi-family construction, older codes like the Uniform Building Code (UBC), Building Officials and Code Administrators International (BOCA), Southern Building Code Congress International (SBCCI), and Council of American Building Officials (CABO). Also, ASTM standards like ASTM C926, ASTM C1063, or ASTM E2112 are often mentioned. Codes often refer to standards published by ASTM International or other organizations. When referenced in the codes, these standards become part of the code. Along with codes and referenced standards, another requirement that must be followed is the manufacturer’s instructions. The requirement to follow manufacturer’s instructions is incorporated into all typical building codes.

I could go on quite a bit more on the subject, but I’m sure you are tired of reading this, or are very depressed. So for now, I think you problems learned more than you wanted to about stucco-and problems.

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