The storm flooded the flower-studded grounds, swamped the wine cellar and buried the gardener's quarters in muck. Two months after Kartina, workers are at war with creeping moisture, trying to repel stench and rot from the Greek Revival mansion and museum in Old Metairie, a National Historic Landmark.
New Orleans - the perennially flooded city platted amid sea, lake, swamp and River - has always battled mold. But since Katrina inundated 80 percent of the city, moisture's assault has hit an all-time high, and a busy army of "mold remediation" crews have come from around the country to dry homes, businesses, schools and churches.
"We've had floods before," says preservationist Daniel Brown Jr., "but nothing like this where houses sat in water for two, three weeks."
A wet building is a moving target: The longer it sits, the worse the mold gets.
"Get some air circulation going, get dehumidifiers going, the air conditioner, throw that carpet away," says Brian Sullivan, a spokesman for the Department of Housing and Urban Development. "If water is coming through the roof, you've got to fix the roof. If you've got a burst pipe, call the plumber. You've got to stop the source of moisture."
The drying-out cavalry rolled in an armada of trucks carrying miles of hoses, thermal imaging cameras and moisture meters. The crews talk enthusiastically about the properties of dew point, relative humidity and air circulation.
"When we were driving in, people were beeping their horns, giving us the thumbs up," says T.J. Lock, a superintendent for the firm Water Out, which dried out the Longue Vue mansion.
At the Old Metairie mansion, trailer-mounted heating systems pump hot air around the clock to dry the soggy cellars while large dehumidifiers keep the temperature and humidity down in the upstairs galleries, the flower arranging room, drawing rooms, library and ornate bedrooms.
"It was a swamp down here," says Steve Vyrostek, a drying out specialist with Water Out, as he walks through the gloom of a narrow passage in the cellar. The water had been higher than his head.
But now, the floors are clean, there's little sign of mold and it doesn't even smell that bad.
The main portion of the mansion did not sustain water damage, but moisture was still a threat in the soupy climate because the air conditioning system went down.
"By the time we got here," Vyrostek says, "the doors and other things were starting to expand, there was light evidence of microbial growth - mold - and there was evidence of cockling - rippling - of paper and the upholstery was puckering."
To battle the rise in humidity, Water Out supplied the mansion with a temporary A/C system and slowly brought down the temperature and humidity.
The building is going to make it through just fine, Vyrostek says. As for the hefty price - tens of thousands of dollars - he doesn't hesitate: His team saved the mansion a fortune.
"They were a rescue team," says the Longue Vue curator, Lydia Schmalz.
What impressed Schmalz the most was how they slowly brought the temperature down. A quick fix warps wood and causes historic plaster to flake.
Similar work is continuing all over the city. At the roof-damaged Mt. Zion Missionary Baptist Church in Gretna, a machine sucks in outside air, warms it up in a furnace to about 220 degrees, and pushes it into the church. Inside, the temperature is sauna-like. The idea is to get that moisture out of the wood by making it evaporate. Once airborne, fans keep the moist-heavy air moving until it's sucked outside.
"What we're doing is creating a drying chamber," Vyrostek says. "I always tell people to think of it as a clothes dryer."
But many New Orleanians, who live with 60 inches of rain a year and who can rattle off the dates of major floods, aren't calling in the experts. They seem hard-wired for fighting mold.
"If the asbestos doesn't get you, the mold will," Robert "Bagg's" Boudreaux jokes as he oversees hired hands carrying out discolored gypsum wallboard.
Boudreaux says he's been through five floods and knows all he needs to know about mold. He's working without pay to clean out the first floor of his landlord's flooded two-story Victorian home in the Mid-City neighborhood.
"My landlord didn't have flood insurance and I'm saving him a lot of money," he says.
Drying out a structure is simple, he insists. First, you take out what's wet - the sludge, the furniture, the carpet, the linoleum, the plasterboard - and strip it to its core.
In the case of many New Orleans homes, that means ripping out layers of history, he says. "We took up carpet, tile, linoleum, tile, linoleum to uncover a beautiful cypress floor."
Once the soggy mess is out, Boudreaux says, you spray bleach and detergents on the wood for weeks to kill the odor and mold.
But Brown, the preservationist, says that common approach has its drawbacks: "It doesn't pull all the moisture out and the smell stays in it for years down the road."
Even so, Boudreaux's landlords - Roy and Laura Sellers - count themselves among the luckier ones in the neighborhood.
"If some people don't get into these houses pretty soon," says Roy, 63, surveying the brown and empty boulevard, "the mold will take over."