Note: This article cannot do justice to this topic. Please accept my apologies for all of the omissions and simplifications. We understand that there are many variations of both materials and installation methods. We also recognize that there is a separate and much more in-depth method for evaluating this cladding system using specialized equipment and invasive testing. Our focus is restricted to the scope of a general home inspection.
What Is Synthetic Stucco?
Synthetic stucco is an exterior wall cladding system from Europe that was first used in North America in the 1960s and became very popular in housing in the 1990s. Originally used on masonry walls, it became popular on wood frame homes. It was used because of its relatively low cost, good insulating levels and architectural flexibility.
We will look at the most common variations, which include the following:
- a sheathing (substrate) such as plywood and oriented strand board (OSB)
- a water-resistant barrier (WRB) over the substrate—optional
- a drainage plane—in newer installations (This may be vertical strips of adhesive over the WRB.)
- insulation board (usually expanded polystyrene) adhered or fastened to the substrate
- a 1⁄16-inch to 1⁄4-inch thick water-resistant base coat (commonly cement mixed with acrylic polymer) troweled on, with a glass fiber reinforcing mesh embedded
- a finish acrylic coat sprayed, troweled or rolled on, which provides the color and texture
What’s in a name? Synthetic stucco may be called EIFS, thincoat, softcoat or PB (polymer-based) stucco. Traditional stucco may be called hardcoat, cement stucco, Portland cement stucco, lime- cement stucco or thickcoat.
How is EIFS/synthetic stucco different from conventional stucco? It’s different in several ways. Here are some: EIFS/SYNTHETIC STUCCO CONVENTIONAL STUCCO Insulation board over the substrate No insulation board No secondary weather barrier on the exterior of substrate Building paper or housewrap on the exterior of substrate Drainage plane on newer systems No drainage plane Polymer-based cement base coat Portland cement base coat Fiberglass fabric mesh reinforcement Wire lath reinforcement Thin, flexible acrylic finish coat Thicker, brittle cement finish coat
Problems With EIFS
Problems with EIFS in homes in the United States surfaced in the 1990s and included class-action lawsuits. The initial problems were identified in the southeastern United States, but problems have been found throughout North America. The problems centered around water damage to wood framing members. In some cases, significant rot was found within the first year or two after construction.
EIFS over wood frame walls forms a watertight skin on the outside of the building. It’s a little bit like putting a building in a plastic bag. The idea is to keep the water out of the building. These systems are referred to as “barrier” or “face seal” systems.
Why Different From Conventional Stucco?
Synthetic stucco problems develop when water gets into the wall assembly through the skin. This often occurs at joints and penetrations. Once water gets past the skin, it gets trapped in the wall and is unable to escape or dry out. The walls are said to have very low “drying potential,” unlike conventional stucco, which is much more porous. Trapped water leads to mold and rot.
Conventional stucco is more porous, as mentioned. Water can move through both in and out. The stucco itself acts as a reservoir. Conventional stucco often has a convenient, if unintentional, drainage plane at the back of the system. A double layer of building paper, for example, forms a great drainage plane.
Common problem areas include the following:
- around and below doors and windows
- at wall penetrations for pipes, conduit, vents, electrical fixtures, railings, etc.
- at roof and deck flashings
- where EIFS goes below grade
- complex architectural details
This illustration shows an older system with no water-resistant barrier or drainage plane.
The joint between the synthetic stucco and windows is a vulnerable area. This system appears to be in good condition with a well-caulked joint.
Workmanship is often an issue, as seen on this windowsill.
Here’s what it looked like when we opened up a wall where the detail work was not so good.
Kickout flashings prevent water from getting behind stucco at the bottom of adjacent roofs.
There is no kickout flashing on this new home. This is likely to be a problem area.
As problems were recognized, the installation approaches changed. A drainage plane was added behind the insulation to allow water to escape by draining down the wall and out through the bottom. This approach addressed the reality that water would probably get through the wall at some point and provided a way to get rid of it.
This illustration shows a more modern approach with a series of drainage strategies.
Don’t bother trying to memorize these assembly details. As home inspectors, we never get to see a cross-section of the wall. We only get to see readily accessible performance issues.
These approaches, introduced around 1997, have not been universally successful and are dependent on good installation techniques and detailing. Vented rain screens using more formal drainage approaches are more successful, but not as common in residential construction.
Differentiating hardcoat stucco from synthetic stucco is largely a tactile experience. Tapping and pressing on hardcoat and synthetic stucco yields very different sounds and feels. Tapping on hardcoat stucco feels like tapping on thin concrete. It sounds solid. Tapping on softcoat stucco has more give, and typically yields a hollow sound or very little sound. Tapping on hardcoat stucco with a bare knuckle hurts more than tapping on synthetic stucco. There is no substitute for experience here.
You may be able to see the fiber mesh reinforcement at openings or surfaces, as we saw on the windowsill in the photo at the bottom right on Page 11. You may be able to see the wall detail at the bottom with a mirror, for example. You may be able to see the insulation, fiberglass mesh or the thick (approximately 2-inch) wall system projection typical of synthetic stucco. By the way, you should not be able to see the insulation or the mesh.
Intricate architectural stucco details including dentils and quoining are difficult to achieve with hardcoat stucco. These details often indicate synthetic stucco. These complex exterior details are also often problematic.
Illustration courtesy of STUC-O-FLEX International. Here we can see the drainage layer behind the stucco. The drip screed/weep screed at the bottom directs water out through the bottom of the wall. In a true vented rain screen, the cavity behind the stucco becomes pressurized by the force of the wind. This reduces the pressure differential across the stucco and reduces the amount of water driving through the siding. We don’t get to see walls and cross-sections, so you won’t often know how the stucco assembly was put together.
Note: There are lots of variations, and there are always exceptions. There are hybrid systems that have acrylic finish over a hardcoat base. There are walls that are hardcoat stucco walls with the architectural details at the perimeters done in synthetic stucco. If you are not sure, do not guess!
What to Watch For
Inspecting synthetic stucco walls is tricky, and the home inspection scope wherein we are visually inspecting readily accessible items presents some significant limitations. Damage to wall systems typically is concealed behind the synthetic stucco skin. We look for evidence of distress and clues that may suggest concealed problems. Here is a list of the most important things to watch for:
- Stucco bulges or cracks (often at or near openings due to stress concentration)
- Dark streaks below the corners of windows and any dark areas consistent with moisture
- Loose stucco
- Mechanical damage
- Unfinished edges and exposed fiber mesh reinforcement
- Stucco extending down to or below grade (It should stop at least 6 inches above grade.)
- Missing kickout flashings
- Poorly installed flashings above door and window openings and at roofs, decks, etc.
- Poorly sealed openings around doors, windows, pipes, conduits, railing connections, electrical fixtures, etc.
- Evidence of patching, caulking and other temporary repairs
- Flat roofs with no overhang (Large overhangs help protect walls.)
Problems around windows are more common than any other. Pay close attention around and below windows, inside and out.
It’s rarely this dramatic, but watch below windows!
Some home inspectors offer stucco evaluation services. This can include inspection with penetrating moisture meters (probe testing), scanning moisture detection devices, infrared thermography, borescopes and so on. There are training programs and protocols that should be considered before offering these. Many inspectors simply recommend further investigation by a specialist for homes with synthetic stucco.
Thanks to Roger Hankey and Kevin O’Hornett for their many valuable contributions to this article.