In North America, EIFS is pretty much a single type of design, namely expanded polystyrene insulation adhesively attached to the supporting wall, and a thin, synthetic, two-layer, glass fiber mesh-reinforced coating system. This type of EIFS is called a “Type PB” EIFS, (PB standing for polymer-based), meaning that unlike traditional stucco, EIFS coatings have a significant amount of synthetic resin in them-the coatings are thus strong, yet flexible.
If you travel the world and look at façade materials, you’ll notice numerous versions of EIFS-like claddings that have names similar to EIFS, and in many ways are actually similar to EIFS used in North America. These similar products share two things in common with the North American type: namely the insulation is a continuous layer that is completely outboard of the supporting wall; and plaster-like coatings as the outside surface. After that, variations abound, and this month’s column will give you an idea of the range of commercially available EIFS-like claddings available around the world.
The idea of placing insulation outboard of a structure that needs insulation has been known for hundreds of years. It goes back into prehistoric times with animals that are externally insulated-like birds and their feathers, and whales with their blubber. The most extreme example of external insulation in modern times is the Space Shuttle, with its 32,000-plus (not a misprint, and not one tile is alike) externally mounted heat-protective tiles, visible as black areas on the underside of the wings and fuselage.
THE ULTIMATE IN EXTERNAL INSULATION
Early attempts at creating externally insulated walls go way back to stucco-like materials, applied onto wood lattices over straw insulation. In a sense, one could even say that a modern building, with a solid concrete frame and walls, rigid board insulation applied on the outside of the concrete with granite panels as the cladding, is an externally insulated wall. However, in modern construction, the term EIFS is usually reserved for plaster-like coatings applied over some form of rigid insulation.
With rare exceptions, insulation materials do not weather well and are fragile (the Space Shuttle comes to mind, again); the sun degrades the insulation and/or they absorb water. The advent of low-density foam plastics (like EPS) and weather-resistant synthetic coatings allowed the creation of a basic modern EIFS design. This development occurred around World War II and was used extensively in Europe to repair and insulate buildings. This type of EIFS migrated to North America in the 1960s and is now commonplace. As noted earlier, the North American market is dominated by a single type of EIFS, while elsewhere in the world there is a much wider range of EIFS-like products.
NORTH AMERICA EIFS
Type PB EIFS dominates the North American market, but numerous attempts have been made to introduce similar products. The type most often encountered is the Type PM EIFS. Type PM EIFS has thicker, harder coatings, and is more like a thin stucco system. Type PM EIFS can use extruded or expanded polystyrene insulation and is often mechanically attached to the supporting wall. Type PM EIFS usually costs more than Type PB, and thus accounts for only a fraction of the North American market.
A variation of Type PB EIFS is the equally rare “Type PI” EIFS (PI standing for polyisocyanurate), a type of insulation, somewhat like urethane. Type PI EIFS is used almost exclusively on wood framed structures. Type PI EIFS is mechanically attached and uses the same type of thin coatings as Type PB.
Other types of EIFS have been introduced into the North American market, with little or no success, including:
Type PB EIFS using rigid fiberglass insulation boards
Type PB EIFS using rigid mineral wool insulation
Spray-applied urethane (which is sanded to make it flat) using Type PB coatings
EUROPEAN EIFS
Building codes in Europe are generally more conservative than in North America, especially regarding fire performance. In some metro areas, foam plastic insulation, which is combustible, simply cannot be used (London, for example). This has resulted in the development of EIFS using noncombustible insulation.
The basecoats in European EIFS are several times thicker than in North America. This creates a more impact- and water-resistant EIFS lamina. This increased thickness is also needed to pass the European test standards for EIFS, which are more strenuous than those in North America.
EIFS AS SYSTEMS VS. COMPONENTS
In North America, EIFS is viewed as a system of components from a single manufacturer. This is not so common elsewhere in the world, where EIFS can be made up of components from a number of producers, such basecoats, finishes and so on. These “design-your-own” EIFS are actual systems but are also sometimes called external thermal insulation composite systems.
In Europe, it’s not unusual to see various brands of EIFS basecoats, finishes and mesh at hardware stores, for use by professional contractors and by DIY people. Customers can thus mix and match them to make their own basic system. In Europe, EIFS is more generic.
In North America, you can find online a number of companies that sell generic EIFS materials that are not part of a complete system until you want a warranty, have job problems or deal with building code issues on a big job.
INDUSTRIAL STRENGTH EIFS
One characteristic of the North American version of EIFS is that its thin coatings do not allow achieving super high-impact resistance, even when multiple layers of heavy reinforcing mesh are used. Although impact resistant is enough for most applications, there are times when much more is needed.
Overseas, there are EIFS-like systems that use metal mesh in lieu of fiberglass. This is not merely metal lath but more like the welded mesh used in sidewalks. The mesh is buried in a 1/2- to 3/4-inch multi-layer, stucco-like basecoat. This provides a hard, very abuse-resistant surface, suitable for all but the worst situations. The outside surface is often troweled smooth, and then painted with a hard paint, like urethane, creating a mar and abrasion-resistant final surface.
EIFS USING FIBROUS INSULATION
When using fibrous insulation in EIFS, a basic problem surfaces, namely: how to get the coatings to stick to the fibrous surface. The highly water-absorptive nature of fibrous insulation means the wet-applied EIFS basecoat and attachment adhesive will seep into the fibers, giving little bond to an already weak insulation material.
Attaching the fibrous insulation to the supporting wall is not that hard: It can be done with mechanical anchors, but the basecoat is another story. One way to deal with this basic issue is to “burn” (or otherwise treat) the outside surface of insulation, creating a crust. The burning of one face of the insulation is done in the factory that makes the boards, which come in large sheets, like plywood. The basecoat and reinforcing mesh can then be applied to the burnt crust. This has been tried a number of times on commercial EIFS but other problems ensued, especially regarding wind pull-off resistance of the EIFS, and the migration of water within the fibrous insulation layer.
In Europe, where the supporting wall is frequently solid masonry or concrete, the migration of water inside the insulation is not so much of a concern as it is with the stud-and-sheathing type walls common in North America. The presence of water in the insulation layer does weaken the insulation (and makes it sag), as well as reducing its insulation effectiveness.
One way to keep the EIFS from sagging and improve its wind pull-off strength is to embed wires in the supporting wall and impale the insulation onto the wires (the wires are long enough to stick out through the surface of the insulation). Metal lath is then impaled onto the wires, and the wires are bent over to cinch down the lath (see drawing). The wire is slightly larger in diameter than a coat hanger and is “shot” into the masonry using a special “gun,” sort of like shooting hanging wires into the underside of floor slabs, to hang ceilings. Stucco is then applied over the lath. In a sense, the stucco “floats” over the surface of the insulation; similar to what happens when stucco is applied to lath over building paper.
This technique can be used with noncombustible fibrous insulation to create a highly fire-resistive wall. The wires are stiff enough to keep the heavy stucco basecoat from making the outside surface sag.
EIFS WITH DRAINAGE
EIFS with Drainage is pretty much unique to North America. It came about as the result of leaks at the perimeter of the EIFS, such as at windows and flashings. The leaking deteriorated the supporting wall, particularly on wood frame buildings. Using EIFS over wood stud and sheathing walls is not common elsewhere in the world, as EIFS is almost always applied over concrete or masonry-walls that are not affected much by water.
The overseas view of leaks is that if you properly seal the perimeter of the EIFS, then you do not need drainage in the field of the wall, since EIFS is seamless and thus there’s no way for water to get in the wall through the EIFS coating and foam.
NEW TYPES OF EIFS
There are some next-generation types of EIFS in the works.
One is a thin, integrally reinforced basecoat that uses glass fibers instead of mesh. The basecoat is smooth and applied all-at-once, and is finished by applying paint. There are also versions of this one-step EIFS lamina that have integral color but there have been problems with color control as they use Portland cement, which varies in color. To get around this, the Portland cement needs to be removed, and the coating then has high resin levels and expensive color pigments, and cures by evaporation of the water. This high resin and pigmentation level makes the basecoat expensive.
EIFS that uses plastic reinforcing mesh has been developed but not commercialized. Plastic has the nice quality that it is unaffected by the alkalinity of the basecoat, due to the Portland cement. Alkalinity can weaken glass mesh, and hence the glass needs to be coated. That’s the good news, but conversely, the bad news is that the plastic stretches more than glass and doesn’t reinforce the basecoat but more importantly, it doesn’t hold the basecoat together properly in a fire, so it’s hard to meet the code requirements for flame propagation.
Although not a commercialized EIFS system, I once got involved with a building that had to have phenomenal impact resistance. We ended up using Kevlar in lieu of glass for the reinforcing mesh. Kevlar is a DuPont-made, aramid plastic-like fiber material and has good, high-temperature properties. It is also five times as strong as steel for its weight, and is resistant to the alkali from the Portland cement in EIFS basecoats. This one-of-a-kind “Kelvar EIFS” could withstand astronomical impact forces, but it costs a small fortune, so was used only for specialty applications; in this case as a tall parapet used to hide and protect sensitive rooftop equipment in a typhoon-prone area. W&C
