EIFS – the search for optimal impact resistance

When Exterior Insulating Finishing Systems came to Canada, the question of how a lightweight exterior wall cladding material would fare against the impact every wall cladding system would face during its lifetime.

Competitors of EIFS products would demonstrate how EIFS could be impacted easily by external forces, sharp objects and bumps from people or cars if such a situation were to arise, giving it a poor reputation as a weaker material at the time. Because of situations like this, EIFS is constantly evolving into a more durable and dependable material. There are many design modifications that can be made to EIFS that allow it to resist impact better.

Reinforcing fiberglass mesh

An important part of EIFS construction, a layer of reinforcing fiberglass mesh is embedded in the base coat between the lamina and the insulating foam. While one of the main reasons this mesh is added to EIFS applications is for flexibility during thermal building expansions, the mesh is also used to provide some impact resistance.

There are heavier grades of reinforcing mesh available that provide much more impact resistance than the standard weight of fiberglass mesh that is used with EIFS. These meshes are typically three to four times heavier than the standard mesh, but can also be difficult to bend and shape around corners as needed. It’s also possible to get heavier mesh that is pre-bent from some manufacturers suited for this purpose.

Today, many installers will make a primary layer with the heavier mesh over the insulating foam, encapsulate it in one type of base coat, and then create a secondary layer with regular-weight mesh as normal. This method prevents an uneven wall due to the overlapping of the heavier mesh, but allows for overlapping of the lighter mesh to leave the flexible properties of the EIFS intact.

Other EIFS materials and increasing impact resistance

Using thicker base coats will give the EIFS increased impact resistance. However, if the base coat is more cementitious than resinous, a thicker base coat can lead to cracking because it may be more brittle the thicker it becomes.

A higher density insulating foam would also offer increased impact resistance, but this can also lead to cracking because of increased stress on the mesh as well as a higher overall cost.

Other solutions

If the particular location of EIFS is vulnerable to being hit with objects, the heavier reinforcing mesh can be used here, and it won’t result in much of an increase in cost due to the fact that the extra-weight mesh is only being used in small areas.

The EIFS in these spots could also be protected by something that offers much higher impact resistance, like stucco or masonry painted with the EIFS finish to match the rest of the wall. This method could increase the impact resistance immensely at vulnerable points but not take away from the aesthetics of the building in any way.

Commercial buildings generally receive far less respect than a home from the public, and if they’re covered in EIFS this can lead to future damage. Many of the larger supermarkets use EIFS and sometimes experience their shopping carts frequently coming flying back at them. Speaking with the designer and architect about what can be done to protect the walls is a good idea, for example, maybe they wouldn’t mind placing a planter or steel bars next to the wall for protection.

Ways of testing impact resistance

Areas that experience frequent and severe inclement weather, such as Florida, have special tests that see how impacted EIFS might become if a hurricane hurled debris at it. Such tests using tornado-like winds would be useful in Ontario, where we’re more than likely to get one or two severely damaging tornadoes per year.

Other forms of testing impact resistance in EIFS is the European “Perfotest” or the North American equivalent of dropping a rod against and EIFS wall. Both methods use a device to put concentrated impact against an EIFS wall, but only the Perfotest, which uses a small spring-loaded rod, is portable and easy enough to use on existing EIFS walls, not on sample walls only.

These developments in impact-resistance and design have allowed EIFS to move away from its former reputation as a “weaker” form of exterior wall cladding, even though exterior walls don’t need a whole lot of impact-resistance. By increasing testing and constantly evolving the EIFS to become a better material, it’s now widely recognized as a strong and durable wall cladding.

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