Stucco is a cement-like coating that is spread on the exterior walls of homes and other buildings. Exterior insulating finishing systems are sometimes called EIFS or synthetic stucco, and are also placed on the exterior walls of homes and other buildings. When completed, both products look the same but have many differences both physically and in the way they behave.

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Stucco and synthetic stucco have many important differences.

Hardness

If the material is already applied to an existing wall, the least intrusive and easiest way to determine whether the material is stucco or synthetic stucco is to knock on it. Synthetic stucco will sound hollow and feel soft, and real stucco will be hard like cement and sound solid when tapped.

Manufacturers and Availability

Stucco is a generic product and is available for anyone to purchase at retail stores. Synthetic stucco is only available to contractors through distributers that obtain each component of the synthetic stucco system from the manufacturer. Synthetic stucco is a three-part system that is installed on-site, and each system is proprietary, meaning each manufacturer owns the rights to their particular system.

Application

Real stucco is similar to cement in that it is a powdered substance mixed with water and then applied to a wall. It may be applied in one to three layers on its own, or applied over metal lath for added strength.

Synthetic stucco is applied in three parts. First, a foam board is secured to the wall with studs. Then, a base coat that contains both resin and cementitious materials are added, in which a reinforcing mesh made of fiberglass is embedded for strength and flexibility. Finally, a top coat that is colored or textured is applied.

Water Intrusion Issues

Both synthetic and real stucco are designed to shed water when it rains or gets wet. However, the soft foam core of the synthetic stucco is susceptible to retaining water if it gets wet due to driving rain, being too close to the ground or improperly sealed nearby joints that allow water to permeate the wall. This retained water can lead to mold and rot, but is only a potential issue if the synthetic stucco is applied improperly and against the manufacturer's specifications.

Restrictions

There are several restrictions on where synthetic stucco can be used and for what purposes that don't apply to real stucco. For example, most North American fire codes prohibit the use of synthetic stucco indoors because the foam board, usually made of expanded polystyrene foam, is combustible. This foam core also prohibits the installation of synthetic stucco at ground level, because this can lead to moisture intrusion as well as ants and termites infiltrating the synthetic stucco.

Real stucco does not have the same restrictions as synthetic stucco. It is non-combustible and can be used indoors, and it does not have a foam core and can be used at ground level without risk of moisture intrusion or pest problems.