The 2-month-old black metal fence surrounding Hempstead House is not designed to deter trespassers. The fence and construction shelters erected over the entrances are designed to prevent visitors from being struck if stones fall from the facade of the historic Gold Coast mansion.

Since the centerpiece of Nassau County's Sands Point Preserve has long suffered from deferred maintenance, the nonprofit group that runs the 216-acre grounds with three historic mansions for the county is kicking off a fundraising campaign this week. It hopes to come up with $20 million to help the county bring Hempstead House back to a state of good repair.

The 40-room mansion was built in 1912 for Howard Gould, son of railroad tycoon Jay Gould. The then-250-acre estate was later the home of steel magnate and philanthropist Daniel Guggenheim and his wife, Florence. Their son, Harry -- who with wife Alicia Patterson founded Newsday -- built their home, Falaise, on the grounds.

A year ago the county began a $1 million project to remedy the most serious problem: rusting steel lintels above the windows.

Lou DiPadova, facilities director for the Friends of the Sands Point Preserve, said "water penetrated the mortar joints, got behind the limestone trim and oxidized the steel, which pushed out and cracked the stone. So now we're at a point where the granite above the window, the limestone trim and also the lintels have to be replaced."

With a $1 million state grant, Nassau hired E&A Restorations of Syosset to replace the rusted beams above the windows with stainless steel lintels. But the company discovered the damage was far greater than expected, said Karli Hagedorn of Sands Point, chairwoman of Friends of the Sands Point Preserve.

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So Nassau suspended the work with three windows done and a fourth to be finished before the company removes its scaffolding from the north side of the house.

"Construction issues beyond the scope of the original project became apparent," said Mary Studdert, spokeswoman for the county Department of Public Works. She said HAKS Engineers of Manhattan prepared a preliminary estimate for the east, west and south facade masonry repairs, and that number combined with E&A's estimate for the north facade plus design, construction management and contingency allowance total $20 million.

While the friends group hopes most of that will come from government grants, Hagedorn said the nonprofit would have to do its own fundraising.

The organization was given day-to-day responsibility for managing the preserve and its buildings in 2008 after acting in a fundraising and support role since its founding in 2003. Its county operating stipend has been dropping annually and is now at $175,000 -- about 10 percent of the operating budget. In 2019 the county operational funding will cease, Hagedorn said.

Film and TV shoots have provided $420,000 a year, and weddings and bar and bat mitzvahs generated about $1 million for programs and maintenance. But Hagedorn said the black fence, construction sheds over entrances and scaffolding has dissuaded prospective event renters in the past year.

The money has paid for daily operations and cultural and educational events. Over the years, the Friends paid $250,000 for air-conditioning, $90,000 to restore the obliterated gardens and about $50,000 to restore an overgrown pond.

Studdert said that between 2010 and 2013 the county spent about $265,000 for electrical upgrades, $200,000 for boiler replacement and $200,000 for repairs to the roof of the summer living room and its interior.

Nassau is supposed to continue paying for capital needs even after the operating subsidy ends. But the county has not done enough preventive maintenance "so there are decades of neglect," Hagedorn said.

To raise awareness about the needs of the site and the new Campaign to Save Hempstead House, the Friends will partner with Atelier Swarovski and Glenn Bradford Fine Jewelry for a "Shop for a Cause" event Thursday through Nov. 22.

The damage "is not just cosmetic anymore," Hagedorn said. "Unless the house is repaired, it will fall down or be taken down."