COLUMBIA - Mistakes that were made during a $5.6 million renovation of the S.C. governor's mansion four years ago are responsible for the mold problem that has forced Gov. Mark Sanford and his family to leave, according to an expert hired by the state.

Making the 148-year-old mansion habitable again will cost taxpayers more than $400,000, said microbiologist Richard Bennett. A more detailed cost estimate will be available next week, he said.

Bennett said fixing the mold problem would have been cheaper had state officials acted more quickly once they first learned of it last August from first lady Jenny Sanford, who complained to the state Budget and Control Board. The board, which owns the mansion and is responsible for its upkeep, hired Bennett's company, RiskTech LLC of Charleston, at the end of June to get rid of the mold.

The firm was in charge of overseeing mold removal at the former Lexington County courthouse, which was closed twice in 2001-02 because of mold.

That was a $400,000 job. The governor's mansion will be more expensive, Bennett said.

"A big part of the price tag for this fix, which makes it different than Lexington, is the replacement of the (air conditioning) system," he said. "That air handling equipment is not cheap."

The Sanfords and their four young sons moved out of the mansion June 21 after tests discovered stachybotrys mold in the air. Although much remains unknown about the health effects of stachybotrys, it can cause serious allergic reactions, health experts say.

According to Jenny Sanford, mansion staff members have developed a variety of ailments, including chronic coughs, dizziness, aching joints and skin rashes. She said her children, ages 5 1/2 to 12, have gotten allergies and chest coughs.

"I, for one, have always had a headache since I've been in that house," she said. The Sanfords moved into the mansion upon Mark Sanford's inauguration in January 2003.

Since late June, the first family has been living in their home on Sullivans Island near Charleston, but plans to move into the pool house -- essentially two sparsely furnished rooms and a small galley kitchen -- on the mansion complex grounds before Aug. 19, when the children begin school.

Bennett said the job should be finished by the first week of September.

He said most of the mold is in the part of the mansion's heating and air conditioning system that forces air through the building's ductwork.

What apparently happened, Bennett said in a telephone interview last week, was workers performing the renovation let the air conditioning system run while they worked on the building's interior, but failed to install filters. A large amount of dust from cutting Sheetrock and sawing and sanding of wood wound up inside the system's ductwork and air handlers, providing a rich source of nutrients for mold to feed on, he said.

"Filters are cheap, and what this problem is going to wind up costing would have bought a lot of filters," Bennett said. "It was entirely preventable."

High humidity in the governor's mansion gave the mold the moisture it needed to grow, Bennett said.

"There are problems with air conditioning old buildings for which it was never contemplated," he said. "You have to do that sort of renovation very carefully, with any eye toward making sure that you don't have condensation."

Besides a thermostat to control the temperature, Bennett said the mansion's air conditioning system should have been fitted with a device called a "humidistat" that makes it run until the humidity is brought down to an acceptable level.

Also, he said, the new air conditioning system that was installed during the renovation was too large for the building, which caused it to shut off before it had run long enough to dehumidify the air.

"When we finish, I think we're going to find problems in three major areas," said Bennett. "I think there were certainly design problems with the system, there were certainly errors made by operating the system during the renovation, and I think we're going to find that after the contractor turned the building back over to the state, there were problems in how the system was operated and maintained."

Officials of R.J. Griffin & Co. of Atlanta, the general contractor in charge of the mansion renovation, could not be reached for comment Friday.

A spokesman for the state Budget and Control Board said it's still too early to assign any blame for possible errors.

"We haven't received back any comprehensive report (from Bennett), indicating certain tasks were or were not performed that should have been," said Mike Sponhour, the board's spokesman. "We're very interested in finding out the answers to that question, which is one of the main reasons that we hired Mr. Bennett and his company, to have an independent analysis of all the factors."

What Are Molds?

Molds are fungi that can be found indoors and outdoors. No one knows how many species of fungi exist, but estimates range from tens of thousands to perhaps 300,000 or more. Mold growth is encouraged by warm and humid conditions. Outdoors they can be found in shady, damp areas or places where leaves or other vegetation is decomposing. Indoors they can be found where humidity levels are high, such as basements or showers.

How Do Molds Affect People?

For people who are sensitive to molds, exposure can cause symptoms such as nasal stuffiness, eye irritation or wheezing. People with serious allergies to molds may have more severe reactions that can include fever and shortness of breath. People with chronic illnesses, such as obstructive lung disease, may develop mold infections in their lungs.