The Finish Line: Backwrapping vs. Edgewrapping
There are two basic ways of terminating the edge of an EIFS. One is by using the EIFS materials themselves, and the other is using some type of non-EIFS trim product, such as preformed plastic or metal pieces. Using the EIFS materials themselves is by far the most common way in North America and is the subject of this month’s column.
Most of the problems relating to water intrusion in EIFS-clad walls occur where the EIFS starts and stops, such as at windows, doors, sealant joints and penetrations. EIFS, itself, is seamless, so how can it leak? Thus, it is very important that these termination details be designed and constructed properly.
There are two ways of using the EIFS materials themselves to terminate the system. The first is to tuck the basecoat, including the reinforcing mesh, onto the back side of the insulation board. The reinforced basecoat may or may not be in contact with the substrate or in the case of EIFS with drainage, in contact with the water resistive barrier. This technique is called a backwrap. The second method is to bring the reinforced basecoat over the edge of the insulation board and bond it to the edge of the opening. This is called an edgewrap.
Edgewrapping connects the edge of the EIFS directly to the side of an opening or to the substrate and locks that edge to the wall structure. The substrate may be some type of sheathing or also a structural member in the wall, such as concrete, block or studs. Edgewrapping seals the edge of the EIFS and protects the edge of the sheathing, if used as the substrate, from water.
Backwrapping, on the other hand, if used on a stud-and-sheathing substrate, leaves the edge of the sheathing exposed. I have seen cases where the edges of prefabricated EIFS panels have been backwrapped and water subsequently got to the edge of the sheathing and turned the sheathing to mush.
HOW FAR TO BRING THE EIFS FINISH INTO THE JOINT?
For both types of wrapping, the issue of bringing the EIFS finish around the corner depends on how the weather seal is created. Usually, the seal is created using wet applied caulking. The caulking needs to be bonded to the EIFS basecoat and not to the EIFS finish. Thus in many cases the finish stops at the face of the EIFS and is not brought into the joint. Some contractors mask-off the sealant bond-to area, to give a clean termination of the EIFS finish in the area where the sealant will be installed.
Edgewrapping does not work when an opening already has something in it, such as a window. Thus coordination between trades is needed. This is especially true with nail flange windows that must be installed before the EIFS.
EIFS WITH DRAINAGE: THE WATER PATH
When using EIFS with drainage, there must be some way of getting the water, if any, that may exist between the backside of the foam insulation and the water resistive barrier, out of the wall. This capability needs to be provided on the lower horizontal termination of an EIFS. This can occur, for instance, at a window head or at the bottom edge of an EIFS wall near the ground. Since edgewrapping seals the edge of the EIFS, edgewrapping can’t be used at such locations. Often the narrow drainage cavity is simply left open or a flashing is used to direct the water to the outside face of the wall. Leaving the drainage cavity wide open at the bottom of a wall near grade can lead to problems, as it provides a route for pests like termites to get into the wall.
I’ve seen special L-shaped “flashings” embedded into the edge of the EIFS at near-grade locations. These flashings are made of fine stainless steel screen, and they allow water to drip out but keep the buggers out.
SMALL UNWRAPPABLE PENETRATIONS
In some EIFS technical literature, you’ll see a note that the edge of the EIFS must be wrapped at all locations where the EIFS terminates. This is not always possible. For instance:
- Where holes are cut through the EIFS after the EIFS has been installed. An example might be a pipe or conduit.
- Where small holes (such as a cable TV wire) passes through the EIFS: there’s simply no room to create the wrapped condition. (In the above two conditions, the edge of the EIFS is simply caulked weathertight.)
- Where access to the edge of this system is restricted and the termination is protected. An example might be the top edge of an EIFS where it abuts the underside of an overhanging roof eave.
Where large objects go through the EIFS, the opening needs to be backwrapped or edgewrapped. Examples of this include windows, doors, large pipes, ducts and the like. There are several aspects of doing “the wrap” that need attention.
If the penetrating object will sag or move up and down (such as a deck beam), the size of the sealant joint needs to be sized to allow for this. The same applies to pipes and ducts that move along their length due to thermal expansion. Likewise, penetrating objects that vibrate (such as an HVAC unit) need to have the sealant joint correctly dimensioned so as to not put undue stress on the joint.
MESH FOR WRAPPING
Many EIFS producers offer special mesh that bends more easily. It’s intended to allow doing sharp corners without the springiness of the mesh pulling the mesh out of the basecoat adhesive. This easier bendability is achieved by either using a lighter weight of glass mesh and/or using a thinner or more flexible coating on the mesh.
Sometimes the wrapped area is a place that is subject to impact damage. An example could be a door jamb. The super heavy weight EIFS meshes are too stiff to bend around sharp corners so EIFS producers offer factory pre-bent L-shaped pieces of heavy mesh to deal with this issue.
WRAPPING IN ADVANCE
Backwrapping of individual EIFS insulation can be done in advance. This can speed up the EIFS installation process by eliminating the somewhat tedious process of wrapping in the field. It’s not unusual, when inclement weather is present, to pre-wrap a supply of “starter” insulation boards at the EIFS contractor’s warehouse and take them ready-to-go to the job site. Edgewrapping cannot be done in advance on field-applied EIFS but is the standard way of doing edges on prefabricated EIFS panels.
WRAPPING IN OTHER WORLDS
In many countries, and especially in Europe, terminating the edge of the EIFS is often done with embedded trim rather than using the EIFS materials themselves. In North America, where we tend to use thin basecoats, it’s hard to get metal or plastic trim to stay put in such a thin coating. In Europe, where the basecoats are normally about twice as thick, embedded trim is common. It also creates a hard, straight, smooth surface onto which to apply the sealant.
Given the importance of properly terminating a seamless system like EIFS, this matter of “how to do it” is worthy of some research and innovation by the EIFS industry. In particular, developing a way to strengthen the edge to provide a secure base for sealants is important. The presence of a hard, non-porous surface also would make replacing aged sealant joints much easier, as the stronger, harder edge afforded by embedded trim is more easily cleaned and prepared for the new sealant, than is a fragile backwrapped or edgewrapped edge. W&C