EIFS – Edgewrapping and Backwrapping
Edge wrapping and back wrapping are two ways of terminating the edges of Exterior Insulating Finishing Systems. Edge wrapping and back wrapping both utilize the EIFS materials that are already on hand, instead of incorporating additional pieces like the use of embedded trim does. In Canada, edge wrapping and back wrapping are far more common, whereas in Europe embedded trim is the edge termination method of choice because their base coats are nearly twice as thick as those used in Canada, allowing for a better grip that holds the embedded trim in place more securely.
These termination points, along with joints, are some of those most crucial components of and EIFS wall, because they’re where water intrusion is likely to occur if the termination is not handled properly.
Edge wrapping is the process of bringing the reinforcing mesh and base coat over the edge of the expanded polystyrene foam and sealing the edge where it meets the substrate. If the substrate is a form of sheathing, it will close it off and protect it from water intrusion.
Back wrapping is the process of wrapping the reinforcing fiberglass mesh and the base coat over the edge and behind the foam insulating board. In the case of back wrapping, it might be in contact with the substrate or the water-resistive barrier if the EIFS in this case has drainage. Back wrapping, unlike edge wrapping, will leave the edges of the substrate uncovered, and if water gets into the opening and gets at the substrate, it can degrade it.
Unlike edge wrapping, which must be done onsite, back wrapping can be completed on prefabricated panels of EIFS because it can be done offsite. This is especially handy if the weather is bad or too cold to apply the EIFS coatings as it could be done at an alternate location, such as a heated warehouse.
Whichever the type of edge termination is used, the question of how far the finish should come into the joint arises. The sealant can’t be bonded to the finish and must be bonded to the base coat, so the finish should stop before this point.
Choice of mesh
Thicker mesh won’t bend or allow itself to be packed into tight corners as easily as lighter mesh, which is available from some manufacturers specifically for edge termination. Thicker mesh, however, offers much more impact-resistance than thinner mesh, especially over back wrapped or edge wrapped areas that are more vulnerable. To compensate for this, some manufacturers will offer thicker mesh that is preformed and shaped to fit the edges of the EIFS.
Another way to make the process of wrapping the mesh and base coat over the edges a bit easier is to use a thinner coating on the mesh.
Applying sealant joints
Embedded trim is a great choice for terminating the edges of EIFS, because it provides sealant with a smooth and solid surface for the sealant to properly adhere to. However, because edge wrapping or back wrapping are typically the termination methods of choice in Canada, there’s some considerations to take when applying sealant to back wrapped or edge wrapped edges.
The specifications for use of sealant also depends on the size of the opening in the EIFS. For larger openings, like those around windows and vents, the sealant joint should allow for the movement that will occur during thermal shifting. This is important so that the joint doesn’t become stressed and rupture. For smaller openings where cables and such are inserted through the wall, calking might be a better option although the instructions of the manufacturer might differ. Back or edge wrapping in these areas is not usually possible.
EIFS with Drainage
When water is introduced to EIFS with drainage, it must be allowed to drain through the bottom. If the bottom is edge wrapped, the water won’t be able to leave the wall because edge wrapping will effectively seal it up the edge, so drainage cavities should be left open to allow for water to leave the wall. Problems arise when this drainage cavity is too close to the ground, as insects can get into the EIFS and then the building or home. There are flashings and trims available with holes small enough to keep bugs out but large enough let water out that can solve this issue.