The ability to create large, seamless, flat wall surfaces is one of EIFS's unique design features. This attribute is not overlooked by architects and is frequently exploited. However, it is a feature that is not without concerns. A comment that sometimes arises from building owners and architects is that the EIFS does not look as "flat" as they think it should. But what is "flat"?
The subject of flatness is a complex one, and is sometimes a source of great debate. Repairing flatness problems can also take a lot of effort. In serious cases it can mean rebuilding the entire EIFS. It's often a shame to go to such lengths, since the waviness of a wall has no effect on its functionality; it's an aesthetic issue. It's also sad that sometimes a lot of moaning occurs about flatness, even though the problem is only apparent under very rare lighting conditions. This month's column provides some insight into the nature of flatness as it relates to EIFS. Hopefully, you will find this article useful in dealing with this sometimes thorny subject.
The flat debateYou should be aware that there is no national consensus standard for what constitutes a "flat" EIFS wall. This can make resolving disputes involving flatness tedious, as there is no scientific criteria for determining what is acceptable. It also makes writing specifications for flatness difficult. However, there's nothing that prohibits inserting some sort of criteria for flatness in a spec, and thus making it a part of a contract. But before doing so ,ask yourself a basic question: What is a reasonable criteria and how is it measured?
Rather than trying to determine a numerical value for flatness, you can define it by example. For instance, if you know that flatness is a big deal on a specific building, then you can make a modest mock-up of the EIFS wall and get the "flatness worriers" to look at the mock-up. Then you can use the mock-up as your standard of comparison for future debates about flatness on that building. This concept is not unlike that of making color and texture samples for EIFS finishes and getting the A/E to sign off on them. Perhaps what would help the EIFS industry in the long run, is a standard for EIFS flatness that is not much different than that used with interior walls. For example, what about having "levels of flatness" standards for EIFS just like there are "levels of finish" for drywall?
Unlike standards for the outside surface of the EIFS, there actually are de facto standards in EIFS industry guide specifications for the flatness of the substrate to which the EIFS is attached. The tolerance for substrate flatness is usually in the range of "so many eighths of an inch, in so many feet," when measured with a long straight edge. Obviously, a very "unflat" substrate can make it difficult to properly attach the EIFS insulation, but it is not impossible to produce a "flat" EIFS wall on a moderately "unflat" substrate. A recognition of this fact is one of the reasons why EIFS manufacturers want EIFS contractors to rasp the EIFS insulation before applying the EIFS basecoat. Doing so is sometimes called "straightening the wall."
Here are some strategies on establishing reasonable expectations on the part of owners and architects about flatness, before the EIFS is installed.
The flat strategies
Know your owner. This means trying to figure out how big an issue "flatness" is to those who will be judging the wall. The on-looker may be the owners (especially if they are occupying the building) or their architect (who passes judgement on the owner's behalf). If the EIFS application in question is a prominent edifice, with a visually-sensitive clientele, then make sure the owner understands the flatness issue in general. Make sure that they also realize that there are limits as to what can be accomplished, in terms of flatness. Owners also need to be aware that a very high degree of flatness is possible, but at a price. As an example, the following dialogue might occur:
"Yes, Mr. Owner, I can make it as flat as a pool table, for an extra $2 per square foot." After doing some quick math, you'll find out how serious Mr. Owner is about flatness. Money talks.
Vast, seamless wall areas are the hardest to "make flat." Unlike other wall claddings, huge jointless areas can be done with EIFS. Unfortunately, flatness obsessions and expectations by owners and A/E's compound the problem on large wall areas. Expressed from a different perspective, joints in the EIFS surface tend to break up the wall into visually separate areas, reducing the cumulative effects of unevenness. Thus gigantic, flat areas are a real challenge and smaller, defined EIFS areas are much easier to build. One way around the obsession that some owners have about trying to create gigantic, jointless, flat elevations is to gently suggest that they add aesthetic reveals or foam shapes to the wall to break up the surface.
"Knowing your building" also means keeping an eye open for other architectural features which can exaggerate waviness. A classic example is lighting at the top of walls. It's not uncommon to use "down lights" at night to create pretty light patterns, by focusing the light beam down the wall in a direction parallel to the wall. This lighting condition can hugely magnify any out-of-planeness of the EIFS finish. Designers and owners need to understand this. Also, they need to understand that this is not solely an EIFS issue but that it occurs with many other wall materials.
Also, usually there are only small sections of a building where flatness really matters. For example, the flatness of the EIFS on the 40th story of a high-rise tower is really often a moot point. This is because all most people can actually see is the color of the EIFS; texture and flatness are realistically non-issues.
Likewise, the flatness of the EIFS, at the bottom of the building near the dumpsters, doesn't matter. What probably does matter are places where people come in and out of the building, and where people can hang around and stare at the wall. Thus you can save a lot of effort in achieving a flat wall by concentrating on developing a high level of flatness only in areas where it is needed. Thus an astute architect might want to specify high levels of flatness in certain areas and let the rest be normal in terms of flatness. This can save time and money.
Know your EIFS productCoarser textures make waviness less apparent. It is hard, with EIFS, to create the very coarse textures often used with stucco-it's just too expensive with polymer-based materials. Rougher EIFS textures are a benefit in this situation.
The use of adhesive fastening methods, instead of mechanical fasteners, can also sometimes help. This is because adhesives have a little "give" to them and thus allow adjusting the outside face of the insulation into a more nearly planar surface. Adhesively attached EIFS also do have plastic washers on the surface of the foam. Washers obviously make it more difficult to rasp the surface of the foam to make it flat.
Also, mechanical anchors rely on a clamping action of the foam against the substrate to develop a tight grip on the wall. This means that the foam needs to be drawn tight against the substrate, which in turn, causes the foam to follow the contour of the substrate. If the substrate isn't flat, the foam will tend to follow the curve of the wall, resulting in a wavy wall. This effect is exaggerated with thin foam, which is more limber than thick foam and thus bends more easily under the clamping force of the fastener.
Thin EIFS basecoats also exaggerate the out-of-flatness of the foam, as the thinness telegraphs the undulations of the foam beneath it. Thick basecoats tend to "bury" the issue. This is one of the many reasons why Europeans use thicker basecoats than we do in North America.
Know the time and weatherThe time of the day and year and weather conditions affect the intensity, color and angle of sunlight. The worst conditions are usually at the beginning and end of the day, when the sun angle is low on the horizon. In this condition, the light tends to skim across the wall, revealing waviness that is often not apparent during the middle of the day. Here's a savvy tip: If you get dragged into flatness arguments, try to arrange your site visit for mid day, when the sun is flat against the wall. Often, the alleged waviness in the wall will not be visible at that time of day.
Lastly, keep in mind that creating a "perfectly flat" EIFS wall is almost impossible. Obviously, the hand-made nature of EIFS makes control of the thickness of the EIFS lamina a matter of plastering technique-an art form, of sorts.
The thinness of the EIFS lamina is part of the problem. Unlike stucco, which can be built-up to make it flat, massive built-up of EIFS coatings is not only expensive, but also can produce EIFS coatings that are too thick, and thus crack prone.
Sometimes, the basic issue of flatness simply needs to be brought up early on in discussions with the owners and their A/E. Many owners, in my experience, simply do not really understand EIFS. This is not their fault, as EIFS is just one of a myriad of issues that they deal with when designing their building. In a sense, they simply often have unrealistic expectations and they need the benefit of your expertise to understand what is practical. It's also comforting for you to know that if you did bring up this issue prior to installing the EIFS, that it'll help your position later on, should concerns arise.
All the above is intended to help you deal with flatness issues before the EIFS is installed. So what do you do if you've inherited a wall that is already decidedly not flat? That's for next month's column, where I'll provide some thoughts on how to loose the flatness without loosing your shirt. W&C