EIFS Sealant Joints and Adhesion
Leaks almost always occur at the edge of the EIFS, such as at a flashing, an adjacent wall element (such as a window or deck beam penetration) or a sealant joint. Sealants are notorious causes of leaks and there are many reasons for this. Besides the obvious issues, such as the sealant reaching the end of its life or the joint not being properly designed or installed, there are lots of other causes.
The tie that bindsSealants, unlike some other types of sealing techniques, rely on developing a bond between the sealant and the adjacent material, such as a metal flashing or a window frame or concrete. Gaskets, in contrast, work by constantly being compressed against the adjacent surface. Compression, not adhesion, creates the seal. The fact that a sealant is in contact with the EIFS does not mean it is bonded to it. This fact can be seen most readily when the wall contracts when it gets cold outdoors and the sealant joint opens up; what previously appeared to be a well-bonded joint is now wide open. Hint: If you suspect that there are bond problems, do your forensic work on a cold day. On hot days, the joint gets compressed, and bond problems are harder to see.
The simple fact of the reliance by sealants on adhesion is the source of numerous sealant-related woes and has many implications.
To achieve adhesion, the sealant must stick to the adjacent material. No kidding. But it must stick tenaciously and permanently. When sealant joints get wider, usually due to the reduction of temperature and resultant contraction of the adjacent materials, the sealant bead becomes stretched because it is being yanked-on by the adjacent materials. This imparts a pulling force on the bond between the sealant and the adjacent materials. This tends to pull the sealant away from the adjacent material. Unless the sealant can remain bonded, the joint may open up, and water can then enter. Many factors affect adhesion and with EIFS there are some aspects of this matter that make EIFS joints different.
The surface of the EIFS needs to be clean in order for the sealant to adhere. This means free of dust, water and other materials that inhibit bonding of the sealant. This means the bond-to area must be inspected prior to applying the sealant. Being a material that has a texture to its surface (yes, even the basecoat), contaminants can get into the texture and be hard to see. Even a barely visible film of water can inhibit bonding. For example, if the intention is to start caulking the sealant joints first thing in the morning, make sure the EIFS is dry. Dew can form overnight on the EIFS and be present at the beginning of the day. Normally, dew goes away as the wall warms up but if you try to apply the sealant against the water film, the sealant may not stick.
Joints have two sides. This may sound dumb but there is no such thing as a one-sided EIFS (or any other) sealant joint. At least one side of the joint is the EIFS and the other (if there is another non-EIFS side) is some other material. Many EIFS manufacturers and sealant producers recommend the use of a sealant primer, applied to the surface of the EIFS, prior to applying the sealant. The purpose of the primer is to fortify the surface of the EIFS, thereby improving the adhesion of the sealant, particular under damp conditions. This means that there may actually be two sealant primers in a single joint: one for the EIFS side of the joint and the other for other side. These primers may not be the same type of primer. It’s a good idea to check various sections of the projects specifications (if there are any specifications!), to see what other types of materials are adjacent to the EIFS. It’s quite possible that the non-EIFS materials may require a different primer, or may even need a different type of sealant.
Many wall materials that are adjacent to EIFS have painted or otherwise coated surfaces. For example, oily, stained wood is hardly a perfect surface to adhere a sealant. Some paints are inherent highly resistant to adhesion of sealants. A classic example is fluorocarbon type paints, often called “Kynar.” These paints have Teflon-like materials in them, and, like a nonstick fry pan, almost nothing adheres to them. Kynar surfaces, which are quite common on metal window frames, and other similar adhesion-resistant surfaces, require special primers.
A little recognized effect that can cause sealant adhesion problems is due to the thermal conductivity of the joint itself. Here’s what happens:
The EIFS portion of an EIFS-clad wall is essentially a solid, unbroken layer of insulation with a seamless layer of coatings on the outside. The breaks in the layer of insulation occur at the perimeter of the EIFS, notably at the EIFS sealant joints. Often in winter, the interior of the building has a higher relative humidity than the outdoors. Thus, the moisture indoors tries to work its way through the wall to reach equilibrium with the outdoor humidity. Unable to easily get through the EIFS insulation, the moisture looks for the next easiest route, and migrates throughout the wall system, usually in the wall cavity. The sealant joint, which is wide open on its inside and which is also uninsulated, allows moisture in the air to get all the way to the back side of the sealant bead before it can go no further.
Because the sealant bead is in contact with the outdoor air, its temperature is at roughly the same temperature as the outdoor air. This causes the moisture on the inside of the sealant joint cavity, when it reaches the inside of the sealant bead, to get colder. This can lead to condensation in the sealant joint. In essence, water is deposited on the edge of the EIFS at the sealant bead. EIFS materials tend to soften slightly when exposed to moisture. This can cause the bond of the sealant to the EIFS to loosen, allowing water from outdoors to get in. The solution: Stuff some insulation into the sealant joint cavity before caulking it shut. This will keep the cavity at a higher temperature, reducing condensation potential. Make sure to use insulation that will not absorb moisture, lest the insulation become a sponge for any water that does get into the joint.
On a similar vein, when sealant joints are horizontal, it’s a good idea to shape them so that water can drain away from the joint. Ledges on the lower portion of the joint, and V-shaped sealant returns, direct water to the sealant area, which can let water into the joint, should an opening develop in the joint area.
Pressure practiceTooling is standard practice when properly installing sealants. The term “tooling” means applying pressure to the outside face of the wet sealant bead, after the bead is in place. Tooling forces the sealant into more intimate contact with the EIFS. Recently, at my lab, I ran some tests to see how much better tooling the bead, vs. not tooling it, enhanced the sealant’s bond to the EIFS. The result: It does make a big difference, especially is tests under wet conditions. It appears that the granular surface of the EIFS results in a need for the sealant to be “pushed” so that it forced into the texture of the surface and comes into full contact. If intimate contact is not achieved, water can get into the voids between the sealant and the EIFS, resulting in reduced bond strength. Thus, even if the sealant bead looks nice and appears smooth, tooling it will improve its performance, not just its looks.
Lastly, should a sealant joint fail and need replacing, here are a couple of thoughts that will save money over the long haul:
Recessing the original sealant bead into the joint by a 1/2-inch or so is helpful. This allows a new sealant bead to be applied over the old one without having to remove the old one. It also allows the new bead not to stand out past the outside face of the wall. It’s an understatement to say that removing and replacing old sealant beads in EIFS joints can be really expensive, hence this simple technique can be a real long-term cost saver.
In Europe, it is common to use “trim” embedded into the edge of the EIFS. This strengthens the joint and provides a clean edge. It also provides a hard, solid surface onto which to bond the sealant. Such surfaces are more likely to develop a good bond to the sealant than the EIFS coatings. Also, if the sealant needs to be replaced, more aggressive methods can be used to remove the old sealant, as the trim can better withstand scraping and cleaning.
There’s a dilemma, though. In Europe, the EIFS basecoat is usually much thicker. This is done for many reasons, but mostly because it makes, in many ways, a more durable wall. This additional thickness has the added benefit of allowing the trim, which is usually metal or plastic, to be embedded fully into the basecoat. North American basecoats tend to be thin and trim pieces sometimes have trouble staying in place in a thin basecoat. One solution is to make the basecoat whatever thickness you normally use in the field of the wall, and to thicken it at the edge where the trim is.
Sealant quality is important, and it’s smart to use the best quality sealant initially, so that the time span between sealant joint maintenance, which should be a regular scheduled maintenance item, is maximized. EIFS sealant joints are so fussy and expensive to remove and replace that you definitely want to do it as few times as possible during a building’s life. Sealant materials are one of those “you get what you pay for” materials. The better ones cost more, but given the tiny percentage of sealants’ initial cost in relation to the whole wall, why be cheap with such a critical wall component?
Finally, reliance on sealants alone to provide weatherproofing is simply not smart. This all-to-common practice is a culprit that lawyers are not shy to identify. There are many ways to provide redundancy to weatherproofing, such as using sealants in combination with flashings, designing the geometry of the joint itself to inhibit water entry, and providing a safe route for water to leave the joint, should it get in.