How to tell the difference between EIFS and Stucco

Many home or building owners cannot distinguish between EIFS (Exterior Insulation & Finish System – or also termed “synthetic stucco”) and stucco. Visually observing the building from a short distance can make it extremely difficult to distinguish between the two systems. With some basic knowledge of the two systems along with a couple of simple hands-on “tests” described in this article, you can distinguish between the two systems with confidence.

Types of EIFS

There are two types of EIFS: PB systems and PM systems. Originally, the different systems were classified according to the composition of their respective finish or color coat. PB, or “polymer-based,” referred to a non-cementious finish coat, while PM, or “polymer modified,” referred to a cementious finish coat. However, today the finish coat composition is no longer the only factor used to classify EIFS, but the PB and PM terms are still used to define the respective EIF systems. It is unlikely that one may encounter PM EIFS, as class PB is by far the most widely utilized EIFS on the market today: according to an EIMA (EIFS Industry Manufacturer’s Association) representative PB EIFS accounts for over 99% of all EIFS clad homes built in the last 10 years.

A PB EIFS façade consists of a base layer of expanded polystyrene (EPS) insulation board (similar to “bead board” foam) attached to the wall sheathing. Additional EPS boards can be cut and rasped, shaped, formed and then placed or “planted on” over the base layer of insulation boards to give the façade the desired architectural features. Next, a thin base coat (typically 1/16″ to 3/32″) is applied over the EPS boards, with a fiberglass reinforcing mesh fully embedded into the base coat. Finally, the finish coat, available in a wide variety of colors and textures, is applied over the base coat.

Class PM EIFS differs from PB in a couple of ways and is much less common in today’s construction as mentioned above. First, the insulation board used is often extruded polystyrene (which has a smoother finish and greater compressive strength than EPS) and the reinforcing mesh can vary between a heavy fiberglass and thin metal lath. The reinforcing mesh is mechanically attached (via screws and plates) to the insulation board and sheathing rather than being embedded in the wet base coat. Next, the base coat, ranging from 3/16″ to 1/4″ thick and containing a higher cement content, is then applied over the mesh (similar to traditional stucco described below.) The finish coat is then applied over the base coat.

PM EIFS is somewhat similar to some of the newer hybrid stucco systems, which consist of hardcoat stucco applied over insulation boards. A discussion of these hybrid stucco systems is outside the scope of this paper, but it is important for the reader to realize these systems exist.

Traditional Stucco

As evidenced by the hybrid stucco systems described above, traditional stucco has changed in recent years. With the advent of fiber-reinforced Portland-cement, stucco systems today are very often two-coat systems (a base and finish coat, but often referred to in the industry as “one coat” stucco), rather than the three-coat systems of yesterday (a scratch, brown, and finish coat). The one-coat stucco system consists of a wire lath attached to the substrate over a weather resistive barrier. Next, an approximate 1/2″ thick base coat layer of fiber-reinforced Portland cement is applied directly over the lath. Finally, the finish coat (similar to EIFS) is applied in a wide variety of colors and textures over the base coat. It is important to realize that EPS insulation shapes can also be “planted on” the stucco base coat to achieve architectural features similar to EIFS. This does NOT, however, mean the façade is EIFS.

Unfortunately, all systems have a finish coat that can be applied in similar colors and textures. Therefore, simply looking at the finish coat will not tell us the type of system. But if we move close enough to touch the finish coat, there are a couple of very simple hands-on tests that one can perform to help distinguish between the two systems. (Note: as described above, a stucco system can also have EPS insulation “plant-ons” or shapes adhered to the base coat. So when performing the tests below, do not choose those areas.)

Hands-on Tests

The first hands-on test could be named the “Tap” test: Tap your fingertips on the façade. Do they produce a “hollow” sound or does it appear to be more solid? The hollow sound indicates EIFS (due to the thinner base coat and insulation board), while the solid sound can be attributed to the thicker, solid stucco base coat and no insulation board (Caution – PM EIFS or hybrid stucco system can also produce a “solid” sound). If that’s inconclusive, use the “Push” test: Press your thumb or finger against the façade. Is there any deflection? Can you feel the façade give a little? If so, you are pressing against EIFS. Again, the thinner base coat over the insulation board allows your finger (or thumb) to slightly deflect the system. On the other hand, if there is no give or deflection and it feels like you are pressing your finger against a concrete wall, then you’re looking at stucco (or those nuisances hybrid stucco or PM EIFS systems). You should notice any deflection with relatively minimal pressure, so do not injure any fingers or thumbs trying to determine if it is EIFS or stucco (I do not want to be held responsible for a “push” test gone awry.)

Of course, there are still many other ways one can distinguish between EIFS and stucco without actually touching it. Just one of these ways is to look for crack patterns in the facade. Properly installed PB EIFS does not typically produce cracks in the field of the wall because of the reinforcing mesh embedded in the thin base coat and the properties of the base and finish coats. If PB EIFS does crack, the cracks will be smaller and typically around penetrations, such as windows and doors where proper joint provisions were not provided. Stucco on the other hand can crack in the field of the wall in addition to at the corners of windows and doors if not properly detailed and installed. Hence, if you observe cracks throughout the wall, it is most likely stucco (or again possibly PM EIFS or hybrid stucco). Another feature to look for are “control joints.” Control joints are (or should be) installed in a stucco wall at corners of windows and doors and within the field of the wall. Control joints are long metal or plastic accessories installed to break up the stucco field into smaller sections to “control” cracking. Therefore, if you observe control joints in the wall assembly, it is most likely a stucco (or PM EIFS/hybrid stucco) system, not EIFS. Be careful not to confuse “control joints” with “expansion joints“, which are typical and required for both systems. Expansion joints are, or should be, installed at all floor lines and changes in substrate for both stucco and EIFS systems. Regardless of the system, both EIFS and stucco depend on the proper installation of a secondary drainage plane behind the system components, flashings, terminations, and sealants to effectively manage water that invariably infiltrates the primary protection plane of the EIFS or stucco.

So hopefully by now when someone asks you, “Is this EIFS or stucco?” you can confidently answer,“I’ll know in one moment, I just have to press my thumb against it!”

Brian D. Erickson, P.E. RRC