Stucco

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Stucco is a rot, rust, and fire-resistant[1] construction material made of aggregates, a binder, and water. Modern stucco is made from Portland cement and water with lime, acrylic and glass fibers added to improve its structural properties.[2] Like plaster and mortar, stucco is applied wet and hardens to a very dense solid. Stucco is durable and can be used for both internal and external uses, unlike plaster which is only appropriate for internal applications.[3]

Stucco should never be painted, as paint will seal the pores and make the material unable to vent moisture causing to rot and mold growth. Instead of painting, stucco can be redashed.[2]

Methods

There are three general types of stucco installation; traditional stucco, exterior insulation and finish system (EIFS), and thin-coat stucco.[1]

Traditional

Traditional stucco application is an exterior grade wall finish made from Portland cement, sand, and lime. It involves applying three coat of material over a metal lath that has been mechanically attached to a wall over its weather resistant barrier. The first coat is called the scratch coat, the next coat is called the base coat or brown coat, and the last coat is a top coat. The diameter of the thickness is approximately 7/8 to 1 inch.[1]

The traditional stucco method can be time and labor intensive and therefore more expensive compared to other methods. This method is also more susceptible to cracking over time due to the natural shrinking of Portland cement as it cures.[1]

Exterior insulation and finish system

The exterior insulation and finish system (EIFS) method, also called synthetic stucco siding, uses up to four inches of rigid insulation adhesively or mechanically attached to a surface. EIFS also consists of a reinforced base coat, a fiberglass mesh, and a textured, protective synthetic stucco top coat. Drainage EIFS incorporates a secondary moisture barrier and a drainage mat with weep holes in the bottom that let the moisture drain behind the stucco but exterior to the wall itself. EIFS is more flexible and softer than traditional stucco, so it allows for ornate keystones and cornerstones that traditional stucco previously could not hold. Because of its inclusion of an rigid insulation layer, EIFS is also more energy-efficient than traditional stucco. The potential downside of EIFS is that it may be slightly more expensive than traditional stucco and is more susceptible to impact damage due to the thin stucco layer and soft insulation.[1]

Thin-coat

Thin-coat stucco has one base coat with a thin finish coat that is typically applied while the base coat is still wet. In some cases, the base coat is a combination of Portland cement, fibers, and proprietary additives. Some abuse-resistant one-coat stucco systems replace the Portland cement with a mineral-based cement like magnesium oxide which creates a harder and more durable finish that is highly resistant to cracking and damage.[1] The thin-coat system is approximately 1/4 inch in diameter.[4]

Thin-coat stucco provides the same durability, design flexibility, and fire resistant benefits as traditional stucco and EIFS but requires less time and labor.[1]

The thin-coat method is the method used to cover insulated concrete form construction.[1]

References