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Usually applied in three coats over masonry materials such as concrete or concrete block, cement stucco forms a protective wall finish that resists assault from an assortment of forces, from woodpeckers to weed-eaters. It may also be applied onto exterior sheathing products such as plywood or oriented strand board (OSB). For best results, a water vapor-permeable, water-resistant building paper (like tar paper) is first attached to the sheathing. Tar paper and similar products protect the wooden sheathing from water that may seep in through the stucco, while permitting moisture inside the wall to escape. The plaster is applied over metal lath or chicken wire fastened over the tar paper and into the sheathing. Lath provides reinforcement and a rough surface onto which the cement stucco attaches.

Cement stucco sheds water well and offers some vapor permeability, unless sealed with a waterproof paint, but it's not breathable like earthen, lime or gypsum plasters.

Components of cement stucco — cement, sand, lime and fiberglass strands — are easy to obtain and relatively uncomplicated to mix. These stuccos can be worked into a variety of textures by altering the size of the sand particles, controlling the consistency of the mix and by using special application techniques. Because cement stuccos are widely used in North America, finding an experienced plasterer is easier than for most other plaster wall finishes.

Despite their ease of application and availability, cement stuccos have the highest embodied energy of all plasters and stuccos, so they're not your most eco-friendly choice. Cement production requires extensive mining and cement itself generates significant pollution in its manufacture.

Cement stuccos also tend to crack, especially around doors and windows. Cracks are difficult to repair and, if not sealed quickly, allow moisture to penetrate walls, damaging wood and insulation. Adding lime and fiberglass fibers to the mix helps prevent this predicament.

Cement stucco can create serious problems when applied to straw bale, cob or adobe homes. Not only do unsealed cracks permit moisture to enter, cement may wick moisture into walls through capillary action, causing water accumulation inside earthen and straw walls, and the eventual deterioration of the walls.

SYNTHETIC STUCCO

Synthetic stuccos consist of sand suspended in a mixture of acrylic polymer, latex and pigments. Applied to hundreds of thousands of homes in North America, synthetic stuccos are purchased premixed in 5-gallon buckets. Application is as easy as stir, scoop and stucco: Simply pop open the top, stir a little, then scoop out the material and trowel it on the wall.

Like cement stuccos, synthetic stuccos are applied over a variety of substrates. The most common application calls for two coats applied over an insulating foam board nailed to exterior-wall sheathing. Synthetic stuccos are typically called exterior insulation and finish systems (EIFS).

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