What is Stucco? EIFS

Advisory Report - May 2003

What is Stucco? 
Part Two of Three:  EIFS

We have all heard the term and have seen it on multiple reports. In these reports the stucco is most commonly referred to as Conventional, EIFS PB, and Hybrid.  Continuing in the series, this month we will move into the discussion of synthetic stucco, or EIFS.

Exterior Insulation and Finish Systems (EIFS) products are often referred to as “synthetic stucco”, “Dryvit” (one of the more common manufacturer brand names), or EIFS. EIFS is described by EIMA (EIFS Industry Members Association) as “A non-load bearing exterior wall cladding system … that interacts to form an energy efficient exterior wall”

EIFS was developed in the early 1950s to help repair postwar Europe. EIFS was introduced in the U.S. in the 1960s, used first on commercial buildings, and later on homes.

EIFS typically consist of the following components:

• insulation board, made of polystyrene or polyisocyanurate foam, which is secured to the exterior wall surface with a specially formulated adhesive and/or mechanical attachment

• a durable, water-resistant base coat, which is applied on top of the insulation and reinforced with fiber glass mesh for added strength

• an attractive and durable finish coat — typically using acrylic co-polymer technology — which is both colorfast and crack-resistant.

Types of EIFS

• Class PB – This system is the subject of several class action lawsuits since it is believed to trap moisture, and, consequently, to cause significant damage to the home. These systems are composed of EPS (expanded polystyrene – open cell foam) or polyisocyanurate insulation board applied to an approved substrate. The insulation board is covered with a fiberglass reinforcing mesh, which is embedded in a polymer based (approximately 80% polymer resin) base coat that is covered with a colored synthetic finish coat. The system thickness, excluding the insulation board, is 1/8 to 3/16 of an inch.

• Class PM, or "Hybrid" Stucco – These systems are composed of EXPS (extruded polystyrene – closed cell foam) insulation board mechanically attached over a weather barrier (felt paper or other house wrap). The insulation board is covered with either: wire lathe, plastic lathe, or a heavy weight fiberglass reinforcing mesh. A polymer modified base coat (approximately 50% polymer resin) is applied to the mesh/lathe and is finished with a colored synthetic finish coat. U.S. Inspect classifies One Coat and Two Coat Stucco with this group. )

• Drainable – These systems are the EIFS industry's answer to the concerns associated with the Class PB systems. These systems incorporate the use of a weather barrier and provide for drainage of incidental moisture infiltration for the areas it is applied to. The remaining components are the same as the class PB system.

Click here to watch a 13-minute video documentary about EIFS.

Click here for more information about EIFS and other stucco systems.

Contributed by Kyle Bost
Senior Technical Advisor
U.S. Inspect, LLC