Stucco – Cement

Stucco – Cement

Three-coat (also called hard coat) cement stucco is installed by applying scratch, brown, finish layers of Portland cement, sand, lime, and water on wire lath placed over a water-resistive barrier, such as building wrap, Grade D paper, or a liquid coating. Two layers of building wrap or paper are recommended because the stucco will adhere to the top layer and interfere with the drainage plane.

The total thickness of all three layers is approximately ⅞ inch. Two-coat cement stucco may be installed on masonry walls and eliminates the scratch coat, lath, and water-resistive barrier. Cement stucco installed since the 1980s often uses a colored finish coat that combines color and acrylics with the Portland cement.

Proprietary one-coat and two-coat cement stucco systems also exist, and are popular in some parts of the United States, such as the Southwest and parts of California. Most systems advertised as one-coat are really two-coat systems. These systems often consist of a water-resistive barrier under a Polystyrene, or other type of insulation board, that is covered by metal lath. One layer of a proprietary Portland cement-based product is applied over the lath to a thickness between ⅜ and ½ inch. A colored finish layer may be applied’ or the base layer may be painted. Painting may not be an approved method of finishing these systems; however, painting is a common finishing method in some markets. These systems are sometimes called hybrid stucco.

Three-coat stucco (two coats over masonry) has been used since ancient times, but is less common today in many markets. This material is also called exterior plaster.

Stucco, especially proprietary one-coat and two-coat systems, should be installed according to manufacturer’s instructions. These instructions may vary based on the manufacturer, the type of system being installed, and the location of the house.

Evidence of water infiltration may not be visible during an inspection. Home inspectors may wish to report this limitation and recommend further evaluation.

Typical Defects Typical defects that home inspectors should report include:

1. inadequate clearance above grade, hard surfaces, and roof coverings (2 inches above hard surfaces and above roof coverings, 4 inches above grade, all clearances per manufacturer’s instructions),
2. absent and deteriorated flashing and sealant around doors, windows, and other penetrations,
3. absent and improperly installed flashing and kick out flashing at wall intersections,
4. absent and improperly installed weep screed,
5. blocked weep screed drain holes
6. cracks, especially at wall penetrations, and bulges, especially at the band joists,
7. damage,
8. efflorescence and spalling,
9. absent and improperly installed crack control and expansion joints,
10. trim slopes toward wall,
11. loose trim,
12. stucco is installed as a roof on a horizontal surface using a standard weather-resistant barrier; this allows water to enter and swell wood below causing stucco cracking.

Standards(1) IRC 2018 Section R703; (2) manufacturer’s instructions.