How to Think About Sealant Joints

Sealant joints are, in fact, a separate cladding assembly – long and thin – that need to be designed and installed just like all other cladding assemblies¹. The joint should have a structural waterproof air barrier behind and a drained backer rod and sealant out front.

Sealant joints around a structure create a spider-web maze of inter-connecting horizontal and vertical ‘claddings’. Air can and will move through the space between the air barrier and the sealant. Moving air can carry water with it. It does not take a big gust of wind to lift water up a drained joint and into the sealant maze. It is not a good thing to have your sealant drainage outlets sucking water into the assembly ². How is a joint designed to stop this from happening?

First, you have to understand that when the wind blows, each building face will experience a different pressure. In a simplified square building, walls facing the wind will experience a positive pressure. Side and rear walls will have a negative pressure. Air that flows around the outside of a building will also flow within interior cavities if they are open. Imagine a cavity being like a drinking straw; negative pressure at one end with water at the other. Experience with drinking straws has taught us that it is not a big deal to apply enough suction to lift water from the bottom of a glass. What has been intuitively obvious from childhood should not be a surprise when detailing sealant joints. Sealant joints are just like drinking straws. To stop the air and water flow just pinch the straw shut in the middle³.

The space between the inner air seal and the outer seal needs to be compartmented (closed) so air cannot flow. This is like pinching a straw. If a straw is pinched in the middle, it doesn’t matter that both ends are open and you are sucking on the straw – no liquid will move up the straw. With sealant joints, the place to put a plug (pinch) is at horizontal joint corners, where the sealant joint changes direction. Vertical joints are compartmented (plugged) at the drain. (see EIFS Practice Manual 3.3.4: Figure 37.)

Understanding that the sealant joint cavity is like an independent, long and skinny straw, should help the EIFS installer understand why ‘wrapped’ EIFS terminations are so important. The ‘wrap’ should restrict the movement of air (and water) from the joint behind the EIFS.

Because joints are a stand-alone cladding system, the drainage cavity in a joint should not be connected to the drainage cavity behind the EIFS or other cladding elements, such as windows. EIFS terminations must be properly back-wrapped to support sealant, to protect the foam from fire and to restrict air movement. There are a few exceptions to this rule. Small penetrations such as pipe penetrations should be completely sealed at the waterproof air barrier and around the perimeter. Water penetration will drain to a flashing at a lower elevation. Joints at flashing and similar locations are designed to drain water and should remain open for that function.

¹ Sealant joints are orphans. They are not part of any cladding although all claddings require some type of closure to adjacent materials. EIFS, by definition, does not include sealant joints. Windows do not include sealant and just about every cladding material that’s out there requires closure with sealant.

² Water has no innate intelligence; it just goes where it is pushed. How it gets pushed to the point it will cause the most damage is pure magic. The devil’s in the details.

³ Research project– try this at home. Try to drink water through a straw that is pinched shut in the middle. If you cause the straw to collapse during the research you’ve exerted enough negative pressure knock a building over.