Water Vapor and EIFS
It's an understatement to say that there is a lot of current interest about the matter of water in relationship to EIFS. Most of this interest centers around leaks of liquid water as a result of precipitation. There is, however, a more complex and insidious form of water that has considerable significance to EIFS. That type of water is known as water vapor, and it is the subject of this months column.
As background, water exists in three forms: as a liquid, as a solid (as ice) and as a gas (as water vapor). Water vapor is not visible, and the amount in the air varies with the location, time of year, weather, and use of the building. For practical purposes the amount of water that is in the air, expressed as a percentage of the maximum amount that it can hold at that temperature, is known as the relative humidity. Hot air can hold more water than cold air, and hence as moisture-laden air gets cooler, some of the water wants to leave the air. The water that does leave the air can take the form of rain, snow or condensation.
Between the linesCondensation usually occurs on the surface of materials, but can also occur within materials. In the case of EIFS, for instance, this might mean water being deposited between the basecoat and the finish. This can lead to deterioration of the EIFS materials, especially if it is prolonged or if it freezes. Another example might be the addition of a layer of paint to the outside of the EIFS finish. If condensation were to occur between the paint and the finish, it might lift the paint off the finish. This type of behavior is sometimes the cause of the blisters you see on surfaces that have multiple layers of paint on them.
Condensation occurring on the inside of single-pane glass windows in cold climates is an example of a cold surface being the medium onto which the excess moisture is deposited. If the material is unaffected by moisture, then you would think that this would not cause problems. However, the water may dribble onto moisture-sensitive surfaces, or may get back into the air again if temperature and humidity conditions change. This can lead to long-term adverse effects on nearby materials.
Another sad byproduct of condensation is that materials generally lose their insulating capability as they get wet. This means that it may cost more to heat and cool a building. In addition, some materials, once wetted, do not return to their original condition. Thus, the wall may be permanently damaged by getting and staying wet.
As you can see from the above descriptions, condensation can cause a number of problems with wall construction, as is to be avoided. To understand how to keep condensation under control, some additional understanding of the nature of water vapor flow in walls is helpful. Here are some basics.
Water vapor travels through the environment in a number of ways. One way is as a part of a mass of moving air. Another is by permeation, meaning a process by which water vapor goes directly through a material. Permeation is a bit like oil going through the oil filter in a car engine. For a given filter (or building material) there is only so much liquid that can go through it. If that amount is exceeded, the amount left over backs up and stays behind. Some materials, like glass and metal, are completely impermeable to water vapor, while others, such a wood and drywall, allow moisture to slowly travel through them.
It is interesting that some materials will shed liquid water, but will allow water vapor to pass through them. EIFS coatings behave this way. Thus when someone says that an EIFS lamina is "waterproof," it's a bit misleading because the lamina will shed water quite well when used as a vertical surface, yet will still allow water vapor to pass through it. However, the EIFS lamina is not sufficiently "waterproof" to allow it to be used as a surface on which water will lay. This is one of the reasons why EIFS should not be used on roof-like applications.
Good work means less waterYou should be aware that the amount of water than can be transmitted through a material by permeation is only a small fraction of that which can be moved by direct physical movement of air. Thus, even small opening in walls, or breaks in vapor barriers, can allow many times more water into a wall than can occur by the water vapor permeating through, say, the drywall. Hence workmanship is important if a vapor barrier is being counted upon to thwart the entry of moisture into a wall.
EIFS has some unusual qualities regarding water vapor that need to be understood in order that condensation not occur within the EIFS or the wall that supports it.
First, EIFS is a laminated material. From the back side of the foam to the outside of the EIFS finish, there are essentially no gaps. This means that the only way for water vapor to get through an EIFS is by permeating through the EIFS materials. This is a slow process, and is one of the reasons why EIFS walls can take a long while to dry out if moisture gets into them.
Second, EIFS is a seamless material. This means that there is little, if any, ventilation within an EIFS wall cavity. This further means that the faster methods of drying-namely by the physical movement of moisture-laden air out of the wall assembly-simply does not occur. Some people theorize that this lack of ventilation, which does result in decreased energy usage, also has the side effect of holding more moisture in the wall. This can lead to various types of problems, and is sometimes referred to as a building that is "too tight," one of the causes of the so called Sick Building Syndrome.
Third, all the materials of which an EIFS is made are partially permeable to water vapor. This includes the insulation, and adhesives and the finish coatings. This means that water vapor can come into a wall by permeation from the outside, or leave the wall by permeating outward from indoors. Thus it's quite possible for water vapor to get into a wall from the inside or the outside, depending on which way the vapor is flowing.
The above three characteristics apply to barrier-type EIFS. Drainage-type EIFS are a different animal. Because there is an open cavity between the back side of the foam and the substrate, some direct ventilating of the inside of the wall assembly is possible. However, drainage-type EIFS have a weather-resistant barrier on top of the substrate, and this material can, depending on what it's made of, impend the ability of water to leave the stud cavity. For example, if building paper is used as the water barrier, the seams that exist where the paper pieces overlap, allows for the direct transport of past the barrier, while still shedding water. In contrast, a continuous, trowel-applied barrier has no seams, and thus the only way for water vapor to get past it is by going through the barrier. Since vapor transfer by permeation is a slower process than direct transport, its likely that wall having water barriers of different materials will have different drying potentials.
In heating climates it is common to place a vapor barrier on the inside of the wall. A vapor barrier is usually some form of sheet material or coating that is highly resistant to the permeation of water vapor. Foil-backed glass fiber insulation has a vapor barrier in the form of the foil, while visqueen plastic film is often stretched across the inside face of the studs prior to installing the drywall. Thus, such a vapor barrier, in heating climates, helps keep moisture that exists in the warm interior of a building from getting into the wall, and therefore helps prevent condensation. However, in cooling climates with high humidity, such as the American gulf coast, water vapor in the hot, humid outdoor air can permeate through the EIFS toward the building's interior, and possibly condense inside the wall.
In regions that are dry and warm all the time, like Las Vegas, water vapor problems are rare. Water vapor problems tend to appear when the outdoor weather is extreme and/or the interior conditions are extreme. Water vapor problems can also occur in regions where the temperature and humidity constantly hover around the dew point. In this case, the outdoor air has little tendency to want to absorb any extra moisture over long periods, and thus a wall the does become wet, does not want to dry out. This is one of the reasons for the common plight of deterioration of wood in the damp Pacific Northwest part of North America.
Clearly, condensation within a wall can have negative affects on the wall. Among the common effects can be deterioration of wood-based materials, staining of interior finish materials, and the development of mold and mildew. From the above brief discussion you can see that the matter of water vapor in EIFS walls can be a complex technical subject. In most cases, EIFS performs quite well in the sense that water vapor issues do not become problems. However, there are some situations where it needs to be looked into on a specific building basis. Here are some examples:
o Cold, dry outdoor weather, with warm, moist interior conditions. Example: a swimming pool building in Edmonton.
o Hot, humid outdoor weather, with cool, dry interior conditions. Example: a cold storage building in Miami.
o Constant cool, damp outdoor weather. Example: houses in Seattle.
There are also some aspects of the EIFS itself that should signal you that the issue of water vapor needs to be checked out. Here are some common ones:
o The use of high vapor impermeable coatings on the outside of the EIFS. This can take the form of paints like epoxies and urethanes.
o The adding of a second EIFS lamina onto an existing lamina, such as may occur during repairs.
o The use of very thick or very thin EIFS insulation layers, and the use of nonstandard insulation materials.
EIFS manufacturers are aware of the issue of water vapor and engineer products so that they perform well under a wide range of conditions. If you run into an odd EIFS application and wonder if there is a water vapor problem, EIFS manufacturers can help you by doing engineering studies that can predict how the wall will behave under the conditions of your specific building.