Stucco may have been wrongly blamed for some leaky homes, says UF researcher

September 15, 2005

GAINESVILLE, Fla. — Stucco, a cement-based product used to coat buildings, may have been wrongly blamed for causing at least some of the leaks that struck thousands of Central Florida homes during the 2004 hurricane season, says a University of Florida expert investigating stucco’s water resistance.

“The intensity of those storms raised some new questions about home construction in Florida,” said Wendell Porter, an assistant research scientist with UF’s Institute of Food and Agricultural Sciences. “We are looking at one of them – how is stucco affected by prolonged exposure to horizontal rainfall? I think it’s too early for anybody to have a definitive answer.”

Porter’s initial findings showed that a water spray simulating ordinary rainfall did not soak through stucco-coated panels even after 10 hours of continuous exposure, he said. But the next phase of the UF study, expected to begin in early 2006, will blast the panels with hurricane-force rain and wind.

“It sounds odd, but we want to stress the stucco to the point of failure,” Porter said. “Then we can duplicate the conditions in a controlled environment and learn how the failures happen.”

The study will help determine whether current construction practices could be improved, he said. But it could also resolve a yearlong controversy over storm damage.

During Hurricanes Charley, Frances and Jeanne, thousands of homes in the Orlando area suffered serious leaks that ruined carpet, drywall and other materials, he said. Some builders made repairs free of charge but others refused, saying hurricanes were “acts of God” not covered by home warranties.

“Homeowners asked what went wrong, and some people were quick to blame stucco, saying it’s porous and therefore leaks were unavoidable,” Porter said. “That’s an oversimplification. There are many variables that could cause a home to leak during a hurricane. As far as stucco goes, the composition, use, application and maintenance could all affect its water resistance.”

A mixture of portland cement and other materials such as sand or lime, stucco is considered a tough, durable coating for the exterior walls of buildings, he said. Stucco is commonly associated with Spanish-style architecture typical of the U.S. Southwest but is also popular in Central and South Florida.

“Once you get south of Ocala, the majority of Florida homes have a stucco exterior,” Porter said. “So we need to understand how to use this material properly in hurricane-prone areas, and the way to find that out is to look at one variable at a time.”

Porter’s initial goal is to determine how much rain and wind it takes to cause significant cracking and leaking in large, stucco-coated panels that simulate exterior wall sections of typical Florida homes, he said.

The study involves 20 panels, all measuring 4 feet by 8 feet and built according to Florida building code requirements, he said. Each panel is slightly different from the others, to make it easier for the researchers to assess which construction formats are more water resistant.

In the first phase, which has been completed, researchers were able to confirm that water did not penetrate the stucco by examining the interior of each panel through a built-in opening, Porter said.

To prepare for the second phase, students in a UF agricultural engineering class are developing a fan-like device to generate winds mixed with water droplets, he said. When the device is built, Porter will cut small sections from the panels and subject them to simulated hurricane conditions, with winds of up to 110 mph.

Once the researchers understand how the panels perform, they will begin a third phase of the study, changing different aspects of the panel construction to try to produce better water resistance, Porter said.

“Eventually, we may be able to recommend some changes to the Florida statewide building code,” he said. “I’m sure we’ll learn things bit by bit as we move along.”

UF researchers may want to pay special attention to the composition of the stucco they use, especially if it includes sand, said Michael Roberts, a stucco expert in Orange, Calif. In the mid-1990s, Roberts and colleagues conducted a study that showed sand quality had a significant affect on stucco’s water resistance.

Sand containing substantial amounts of clay encourages leaks, he said, because clay particles expand dramatically when wet and then shrink as the stucco dries, leaving empty spaces where water can enter.

“We tried out many different combinations of materials, and we found pretty much what we expected,” Roberts said. “The poor quality mixtures leaked, and the high quality mixtures did not.”