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A Tale of Two Types of Stucco

The biggest reason why this home owner chose stucco instead of brick for his house is the fact that it could be tinted any bold color he and his wife, Julianne, wanted.

If you're not building a rectangle, why use them as building materials?

That's one reason architect Matt Schlueb decided to forgo brick or siding and use stucco on his unusual house in Franklin Park, Pa. But the bigger reason he chose this ancient material (and plaster, its interior counterpart) is the fact that it could be tinted any bold color he and his wife, Julianne, wanted.

Schlueb initially planned to use only synthetic stucco, a lighter, more flexible acrylic-based alternative to conventional stucco, which initially was a mixture of hydrated lime, sand and water, with animal hair or straw as a binder.

In the 1800s, Portland cement replaced most of the lime in the mixture, which must be applied in two or three coats over several days or weeks, upon a substantial base of masonry or wood or steel lath.

Synthetic stucco appeared first in Germany in the 1950s but caught on in America during the building boom of the 1980s and '90s in the South and Southwest. Known as Exterior Insulation and Finish Systems or EIFS, synthetic stucco was popular with builders because it was cheap, fast and easy to apply, could be colored, and combined siding and insulation in one product.

Tens of thousands of new homes were covered with synthetic stucco that not only looked good but also had up to an R-13 insulation value, thanks to its base, polystyrene foam board.

Then the complaints started to roll in, resulting in lawsuits and a class-action suit against manufacturers, builders and installers. The problem was moisture getting behind the stucco through the edges of doors and windows and other openings. Trapped there, it rotted the wooden studs and other building materials, sometimes leading to mold development.

By the late 1990s, after paying millions of dollars in judgments and settlements, EIFS manufacturers had designed new systems with drainage channels to allow moisture out. But the damage had been done. Although EIFS remains a popular cladding for commercial construction, accounting for 30 percent of the market, it holds just 3 percent of the residential siding market.

Why did Schlueb use it? Because Senergy's EIFS seemed perfect for a house with curving, sloping walls with no right angles. The foam board, fiberglass mesh reinforcement and flexible base and top coats could follow every bend. But it turned out that plywood, which is installed between the studs and foam board, was not so flexible. It wouldn't easily bend in two directions.

So Schlueb and his installer turned to conventional stucco, also made by Senergy. It was used on the curved upper portions of the house, many of which also slope outward. Synthetic stucco was used on the lower portions, where the walls are more vertical. The top coat on both products is a flexible acrylic coating like the one used for EIFS.

Although local installers rarely use both conventional and synthetic stucco on the same project, it's common to topcoat conventional stucco with acrylic or rubberized coatings because real stucco often cracks, said Rick Haarbauer, president of Exterior Products of Pittsburgh, which supplies Senergy products.

"People like the look of stucco but are worried about EIFS," he said. "You show them how the drainage system works. Confidence is slowly being restored."

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