Stucco

In the building code, stucco goes by another name: cement plaster. It is a wet mix of cement, sand, and water troweled or sprayed onto a wall in layers, then finished for color and texture. The 2021 International Residential Code covers it in Section R703.7 and ties it to ASTM C926 for the plaster and ASTM C1063 for the lath.

Three-coat stucco is the traditional method. A scratch coat of 3/8 to 1/2 inch goes over metal lath, a brown coat of 3/8 inch levels it, and a finish coat carries the color. Total thickness lands near 7/8 inch and the wall picks up 10 to 12 pounds per square foot. Section R703.7.2 requires at least three coats over lath, and two over masonry.

One-coat stucco is misnamed, since it also takes a finish coat. A proprietary fiber-reinforced base goes on at a minimum of 3/8 inch, often over rigid foam board, not open framing. The code does not write it out, so each brand is approved as an alternative through an ICC-ES report under criteria AC11. The wall ends up thinner and lighter, near 4 to 6 pounds per square foot.

The difference is a real line item. One-coat dominates metro Phoenix production subdivisions because it goes up faster and costs less, while custom work here more often specifies three coats for the added thickness and impact resistance. For example, a Cave Creek home gets scratch and brown coats that cure for days before color goes on. Both systems sit over a water-resistive barrier and stop at a weep screed.

Fine cracks come with the material. Cement plaster shrinks as it cures, so a rigid coating over a moving wood frame shows hairline cracks. Stucco is also not EIFS, a look-alike built from foam board and acrylic rather than cement. Ask which system your bid prices, because the two are not the same wall.