Stucco is really just another word for Portland cement plaster, which is made by mixing Portland cement-based materials, water, sand, and certain aggregates. The plaster is then sprayed on or applied to the home’s exterior in two or three coats, until it reaches a specified thickness. "Stucco can be applied directly to a concrete or masonry substrate, or to a metal lath attached to construction framing," says Terry Collins, a concrete construction engineer for the Portland Cement Association. A water-resistant building paper typically separates the stucco from framing or sheathing.
In a three-coat system, a scratch coat, brown coat, and finish coat are applied in that order for a 7/8-inch thick stucco surface. A three-coat application often has mesh reinforcement embedded in the base coat and filled with a brown coat for greater strength and adhesion. Stucco can be prepared on site by the applicators or commercially prepared and mixed with water before application. One benefit to stucco is its ability to breathe while retaining moisture during the curing process. It is this long curing process that makes stucco so impact resistant. Cost varies by region, market, and the nature of the job, but stucco is usually priced from $4-8 per square foot applied.
Depending on the size of the job, a complete stucco finish can be applied in one day, but stucco’s curing and strengthening process can take up to 28 days. "Portland cement gains strength over the first 28 days," says Collins. It can also gain incremental strength over decades. Ideally, a stucco exterior is applied after interior electrical, HVAC, and drywall work has been completed, to avoid unnecessary vibrations and hammering that could cause cracking and adhesion problems as the stucco sets. Unfortunately, says Collins, contractors frequently apply stucco immediately after the framework is up, before interior work is completed, which can result in callbacks and repairs.
Color, Texture, and Finish
The color and texture of stucco’s finish coat is achieved by adding color pigments to the mixture, using colored or tinted cement, or by using a colored finish or final coat. In their unique four-step application process, Perma-crete, of Nashville, Tennessee, sprays on a stain sealer as a final coloring and staining coat. "Our stain sealer is essentially an acrylic-based emulsion—it gives color, protection from UV, and water-resistance," says Don Tiskevics, vice president of sales and marketing for Perma-crete.
Textured stucco is achieved in two ways, either by altering aggregate sizes in the mix or by manipulating the texture during application. Hand-textured stucco is a blend of artistry and craft, so it’s best to see examples of the applicator’s work before you hire an applicator.
Stucco Upkeep and Repair
As with many exterior or siding products, stucco can get dirty. When dirt and grime collect on a stucco surface, a garden hose and household cleaning detergent can do the trick. "We recommend spraying the surface first from bottom to top, and then rinsing it from top to bottom," says Collins. "If persistent dirt remains, detergent, water, and a scrub brush should work." Collins does not recommend a pressure washer, as too much pressure can crack, chip, or loosen the stucco.
"Quality of installation, surface conditions, and physical abuse can all play a part in repair needs," Collins says. Cracks smaller than 1/16 inch might not need immediate attention, but larger cracks should receive a good cleaning, followed by a mixture of sand and Portland cement packed into the cracks. A fog coat, or pigmented cement and water coat, should then be sprayed onto the crack or applied by hand. "I don’t recommend homeowners take it upon themselves to do big repair work to stucco," says Tiskevics. "It is a job for the installer."
Credit: Renovate Your World