Sealants, 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.
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.
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.