U.S. Inspect - Professional Home Inspections: Exterior Stucco

Stucco

Stucco is an exterior masonry product made from sand, Portland cement and water. It is generally applied over metal lath or masonry in two or three coats. The first coat is approximately 3/8 inch thick, and is called the “ground” coat. The second coat is also approximately 3/8 inch thick, and is called the “scratch” coat. The third coat is the finish coat and is approximately 1/8 inch thick. The total thickness should range from 3/4 inch to 1 inch.

Stucco over frame is likely to exhibit hairline and alligator cracking because the frame is much more flexible than the stucco. Expansion/contraction joints should be installed in stucco installations every 144 square feet of surface without penetrations however, they are rarely found in residential construction. If the cracks cannot be filled with paint or a minimal amount of caulk and paint, there may be a problem. The problem could be workmanship, stucco mix, wet lumber, a large number of openings, or the structure.

A common problem with stucco as it gets older is that water may get behind it and cause the stucco to separate from the wall. The areas where this is most likely to occur is below windows and where rainwater drains off of a roof, and runs down the stucco wall.

Recommended, Dependable Stucco Repairs

The loose, separated stucco should be removed

Metal lath or a clean, porous masonry surface is necessary for proper adhesion of the new stucco. Metal lath should be “self furring galvanized steel,” and should be installed right side up. This will allow the stucco to key properly around the metal lath.

The stucco mix should not be too rich because it will crack easily (too much cement).

The stucco mix should not be too weak because the surface will be sandy and the adhesion qualities will be suspect (too much sand or water).

If you have difficulty getting the stucco to adhere, such as on a ceiling, lime can be added to the mix.

The proper mix is one part cement, three or four parts sand and just enough water to get the sand and cement to mix. This will vary based on the moisture that is already in the sand. 1/2 part lime will improve adhesion.

The color and texture of stucco repairs are very difficult to match. Painting the wall after a reasonably close match of the texture should be satisfactory in most cases. Use of an elastomeric paint is recommended for this purpose.

Cost of repairs are subject to the amount of repairs needed, the age of the stucco and the difficulty of the job. The range should start at a minimum of $300 for anything up to about 50 SF, plus about $5 per SF for the next 300 SF. As the amount of repairs increases, the SF cost should stabilize or decrease a little. New stucco should cost approximately $3.50 to $4.00 per SF.

Assuming a good mix and workmanship, stucco is relatively stable for about 20 years with no more than discoloration along the base and at windows. After 20 to 25 years, the stucco may begin to absorb moisture. The moisture, especially if it freezes, will break down the surface, and by the time it is 50 to 60 years old, it may require replacement. The best way to determine the condition of stucco is to rub a gloved hand along the stucco to see how much sand falls off the wall. The quantities should be minimal. If sand cascades off of the wall, it is evidence of considerable deterioration.
The typical life expectancy for unpainted stucco is about 50 to 60 years, assuming it is mixed and installed properly, and dependent on its exposure to weather and the sun. If stucco is painted periodically, it can last 200 years or more.

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