interior of a flood damaged house with level marks for mold line, flood repair recommendation and actual flood line
Photo: Katherine Slingluff
Rashida Ferdinand exposed the studs—added in a 2005 renovation—on her New Orleans house by removing the drywall to a foot above the flood line.
As soon as Hurricane Katrina's floodwaters receded, Rashida Ferdinand raced to save her 1892 shotgun house in New Orleans's Lower Ninth Ward. As experts recommended, she ripped out 4 feet of her almost—new drywall, a foot higher than the muddy water had risen. She pulled out the fiberglass insulation between the studs she'd recently added and scrubbed the remaining surfaces with bleach. As she left the walls to dry, she felt relieved and lucky: "I thought I'd escaped the mold."

Two years later, after plans and permits and financing, Rashida was ready to continue the renovation she had started before the storm, and This Old House TV began documenting her—efforts. But when TOH master carpenter Norm Abram arrived at her house, he explained what happens when wind—driven rain penetrates siding, preparing her for some unex­pected news. Since the original walls behind the new studs and insulation were of traditional barge board—vertical planks ­salvaged from old riverboats—that had been lined with burlap and nailed-on drywall, he told her more demolition would be needed. Then he pulled off a piece of the old wallboard behind the studs and found the back spotted with mold. "He knew," she says.

In a way, Rashida had escaped the worst. Her mold was found before new walls covered it. But all around post-­Katrina New Orleans—and in countless other flood-damaged areas—homeowners have replaced only the most visibly damaged drywall, effectively preserving mold still living behind it.

Mold is a microscopic spore that is always circulating in the air. Spores will take hold and multiply anywhere there's moisture and available cellulose—plant material—for them to feed on, such as drywall paper and wood. It doesn't take a flood to bring mold on; a leaky roof or a humid summer can nurture its growth. The danger comes when the spores become airborne in great numbers; then it's likely they will overload a person's —immune system, triggering an allergic —reaction—wheezing, skin rashes, and ­other debilitating symptoms—or exacerbating life-threatening asthma. The only way to stem mold growth is to remove surfaces that provide a good host, clean what remains, clear the air, then rebuild, taking preventative measures.Remove What You Can

The U.S. Environmental Protection Agency suggests that homeowners might need help from a professional if they find mold on an area more than 10 square feet in size, but after big floods, that's not always possible. So the EPA has published guidelines that even inexperienced homeowners can follow.

Once Norm discovered the mold, on went the respirators and out came the pry bars. People can be sensitized to mold through the skin as well as the lungs, so rubber gloves, goggles, and a respirator—the EPA recommends a double-elastic disposable labeled ­"N-95"—are all important.

Careful mold removal begins by sealing off the area with plastic over the doorway. Then all absorbent materials (including carpet, drywall, and paper items) have to go. "Take walls down to the studs," says Rebecca Morley, director of the National Center for Healthy Housing in Columbia, Maryland. Even though most guidelines say material a foot above the floodwater mark can remain, "you actually do need to go further," Morley says. Researchers measured mold levels before and after cleanup in four demonstration homes and found that spore counts dropped to a background level in the three where crews removed all the drywall, but stayed alarmingly high in the one where they only took away the bottom pieces.

No one knows how dangerous it is to leave mold trapped in inaccessible places, such as inside walls or behind cabinets. "With lead and asbestos, you can manage it in place," Morley says. "But mold is a growing organism. Even behind a cabinet, I'd be leery about whether it is truly contained."

For Rashida, the decision was easy. The demolition phase was the time to get rid of questionable materials, including the old drywall and burlap covering the barge boards. She didn't want to worry later about shortcuts she took.Clean Up and Clear the Air

For many years, people were told to fight mold with bleach, which does kill the spores. But today, health researchers know that dead spores are just as dangerous as live ones. "They're still allergenic," Morley notes. Bleaching away spots just makes it hard to see that there's mold present in the house.

Removal is the real cure. But how, given their microscopic size? Rashida worked with Dr. Eric Griggs, a pediatrician whose practice had evaporated after the flood and who saw a pressing need for careful cleanup before families could safely return. He became certified in mold remediation and started a cleanup company called EnviroMed.

Removing mold is a two-step pro­cess: First, loosen the spores; then suck them up with a HEPA-filter vacuum. Though you can do this with a stiff brush and a vacuum wand, Griggs uses a system invented to help restore the Statue of Liberty in 1986. He blasts the surface with baking soda, which ejects the mold without damaging the wood.

Once he'd vacuumed up the debris at Rashida's house, Griggs sprayed the wood with MDF-500, an EPA-­approved biocide that would kill any bacteria that might have been brought in by the flood. Later, an exterminator sprayed the wood with Bora-Care with Mold-Care, a borate solution that fights mold and protects against termites, ­carpenter ants, and wood rot.Rebuild Smarter

Rashida's house sits on piers 3 feet above grade, but when the levees broke the area was flooded with 6 feet of water. So unfortunately, her main protection against future flooding is faith that the levees will hold. But for many of the city's citizens who live in postwar housing, a first line of defense is to elevate their homes to weather a storm surge, a traditional building practice in the area.

Beyond just keeping out of a flood's path, innovative construction practices can minimize the chance of mold coming back. At Louisiana State University in Baton Rouge, Claudette Reichel oversees La House, a demonstration home that showcases both essential measures and what she calls lagniappe, Louisiana French for "a little something extra."

Essential antimold steps include ­sloping soil away from the house, ­water­proofing the roof by tying it down with extra fasteners and special edging to ­resist wind, and assembling walls with interior air flow so moisture can ­evaporate. In hot, humid ­climates like that of New Orleans, moisture usually moves from the outside to the air-­conditioned inside, so a sealed interior surface creates a habitat for mold in the walls. "No vinyl wall coverings, no impermeable paneling," Reichel says.

Some lagniappe approaches are simple, like leaving a gap (covered by chair rail) between a wall's lower and upper drywall panels so moisture can't wick up, limiting flood damage. At the other end of the scale is what Reichel calls a "drainable, dryable wall." You move the wiring above the flood level and spray a 2-inch-deep layer of closed-cell polyurethane foam between the studs. Leaving the rest of the space empty, you screw on paperless drywall, which contains nothing that mold can feed on, but you create small gaps at the top and bottom that are then covered by crown molding and baseboard. If another flood occurs, you just pry off the molding, flush out the wall cavity from the top, vacuum up the water at the bottom, and set up fans so the wall dries quickly. "If the house were under water for six weeks, the paperless drywall probably wouldn't survive," Reichel says. "But with shorter-term flooding, it would often be restorable."

The preventive measures at Rashida's house will take their cue from these recommendations. The walls will be finished with Georgia Pacific's Dens­Armor, a paperless drywall, and the insulation will be Icynene, an open-cell spray foam that contains nothing cellular for mold to feed on. Icynene is porous, so as long as floodwaters aren't contaminated, the insulation will drain and dry out easily with no lasting ill ­effects. So if there is another disastrous flood, with a little cleanup, Rashida will be able to return to her house quickly, relieved to know that this time she has truly escaped the mold.
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