Impact resistance of EIFS walls

Building and home walls generally do not require much impact resistance. There are few situations where an object is actually going to hurl itself at an exterior wall with enough force to damage it.

That said, it can still happen – a new driver accidentally stepping on the gas instead of the brake, a renegade soccer ball or hockey puck, or the ladder you use to install holiday decorations landing up against the wall with a solid “thud”. These issues don’t apply to only homeowners, as anyone who’s ever been to the grocery store knows how hard people in a hurry will thrust those carts at the walls near store entrance before running back to their car.

The EIFS installed on the exterior wall of the second story of a building, for example, is not as much at risk for sudden impact as other EIFS locations. Some of these vulnerable spots include:

• Areas frequented by general maintenance activity, such as around windows that receive visits from cleaners, sides of buildings that might accidentally come in contact with a snow shovel in winter months, or as mentioned above, areas that may be patronized by a ladder every so often.
• An area trafficked by people, or where people congregate. Near sidewalks, walkways, driveways and balconies.
• An area trafficked by vehicles of any type: snow plows, snow blowers, cars, lawn mowers, construction vehicles.
• An area that contains or stores “stuff”: bicycles (who hasn’t thrown their bike up against a wall as a kid in a hurry?), equipment, pool supplies and toys in the winter, construction materials or those wood panels for your new deck.

Testing the impact resistance of EIFS

Much of the impact resistance testing of EIFS in North America is done in laboratories and designated facilities as it is highly unlikely that a building or homeowner will allow on-location perforation experiments of their brand new EIFS wall. However, this laboratory research has provided the North American EIFS industry with valuable information on impact resistance, and how the materials used in EIFS affect their ability to withstand impacts.

In Europe, the birthplace of EIFS, testing the impact resistance of EIFS is much more advanced than in North America. Across the pond, they employ a specialized portable device that will only puncture a wall if it is of poor construction or not impact resistant enough – called the “Perfotest”.

Special precautions should be taken with the aforementioned vulnerable areas, as their high-trafficked nature and being surrounded by activity can lead to an accidental dent or two.

These measures include:

The choice of foam used: the expanded polystyrene (EPS) foam is what is commonly used today, but it has a relatively low density. Other forms of foam such as extruded polystyrene foam were common decades ago and not so much today, and are far denser, offering more resistance to impact.

Increasing the amount of reinforcing fiberglass mesh. Heavy-duty mesh is available that weighs significantly more than the standard mesh, but offers that much more impact resistance. A further layer of standard reinforcing fiberglass mesh is then incorporated with the heavy-duty mesh. Because of the thickness of the heavy-duty mesh, the edges must be butted and not lapped as per usual. Too much reinforcing mesh can also have implications in the application process, making it more difficult for coatings to attach themselves to it, and this must be taken into consideration.

• Base coat types and thicknesses can be an important factor in the overall impact resistance of EIFS. A much thicker, noncementicious base coat will encapsulate the reinforcing fiberglass mesh much more efficiently, increasing the flexibility of the wall and reducing the likelihood of cracking.
• The type of substrate upon which the EIFS is clad may be either hard or soft. If it is softer, the EIFS can stretch more easily to absorb more the impact with the substrate, whereas with a hard substrate the EIFS must take the brunt of the impact.

Employing some of these methods will increase the impact resistance of the EIFS wall, and EIFS manufacturers recommend that these precautions are taken at least six feet above the vulnerable area.