Stucco is an all-purpose term that may be applied to interior and exterior wall surfaces. The word originally referred to a cement-like rough exterior finish, and that's still its correct usage. But faux interior techniques are also called stucco, or properly identified as decorative plaster finishes.
Stucco that covers the outside of a home is a rock-hard mix of Portland cement, water and sand, and is called traditional stucco. Typically, traditional stucco is applied in three steps over a moisture barrier: the scratch coat, followed by the brown coat and the tinted texture coat. Because the texture coat contains color, there's no need to paint or otherwise finish the exterior. Texture may be applied with a variety of rough, swirled, smooth and decorative flourishes for architectural styles, from Santa Fe to Santa Barbara. Traditional stucco stains and ages organically over time, resulting in interesting color variations.
Synthetic stucco is a one-coat finish made of foam insulated boards covered by a polymer-based synthetic coating or acrylic resin that looks like stucco. It is known as EIFS -- exterior insulation and finish systems -- and is a durable exterior cladding that lasts as long as or longer than traditional stucco, but retains its original color and shows no weathering. Synthetic stucco wasn't developed until the mid-20th century, so it is common on more contemporary houses and commercial buildings, and it has a history of structural problems that the industry continues to try to resolve.
The stucco finish applied to interior walls is really plaster, and might come from a kit containing acrylic polymers and clay, or be mixed in traditional formulas based on lime and water. Once you've prepared the wall for painting, the application of interior stucco is generally a two-part process:
- Use a blunt-cornered spatula or steel trowel to apply the first coat of plaster at about a 15- to 30-degree angle. Swirl and vary the plaster to create your chosen texture and leave glimpses of the wall showing.
- Once that's dry, the second coat goes on at a 60- to 90-degree angle -- the trowel is more perpendicular to the surface, and this causes greater variance in the texture.
The tint is in the plaster, so the wall doesn't need painting. Once the top coat is dry, you can burnish the plaster to create various degrees of shine. Polishing with 600-grit sandpaper gives the plaster a gleam. Pressing and rubbing a flat steel trowel on the plaster results in a glossier shine.
All About the Texture
Choose from multiple texture styles when applying, or contracting for, a stucco finish. The rougher finishes are appropriate for exterior plaster.
- Cat face is smooth with random scrapes that resemble paw prints across the surface.
- Dash is sprayed on and is rough and pebbly, like a fine popcorn finish.
- Lace requires a hand-applied rough, thick top coat that is then knocked down with the flat edge of a trowel to create a lacy pattern.
- Sand or float can be fine, medium or coarse; you flatten a fairly even final coat by pouncing it with a float.
- Smooth looks like skim coat -- a very thin top coat with few lines -- smoothed nearly flat with an oversize pool trowel. Extra color may be applied to make a mottled finish.
- Worm uses a top coat with cruder aggregate -- lumpier plaster -- that's then rubbed with pressure in a circle to leave "worm trails" in the finish.