The National Aquarium at Baltimore will shut down two of its centerpiece exhibits, the coral reef and the shark tank, for repairs next year -- an $8.6 million project that could last up to 20 months -- while workers fix concrete corroded by salt water.
David Pittenger, the aquarium's acting executive director, described the work, scheduled to begin in September 1992, as maintenance.
"It's like a sidewalk that gets salt put on it all winter. After a while, it begins to chip, and you have to repair it. That's what we're looking at doing."
The 10-year-old aquarium, second only to Harborplace as a Baltimore tourist attraction, cost $21.3 million, most of that city funds.
More than 1.5 million visitors toured the building in the fiscal year that ended last June 30.
City Hall has budgeted $3.75 million so far toward the repair project: $250,000 for design work in fiscal 1992 and a $3.5 million bond issue in fiscal 1994.
Mr. Pittenger said he expects the aquarium will raise much of the rest of the construction budget privately.
Edward J. Gallagher, the city's budget director, said the city is obligated to share maintenance costs but cannot promise to pay more than what it has committed so far. "We're poor," the budget director said.
Mr. Pittenger said the repair project includes moving some of the displaced marine life to other areas, so that visitors will not miss any of the exhibits while construction is under way. The aquarium staff also is considering installing "a multi-media exhibit" on the ramps alongside the tanks, to give visitors something to see as they wind their way down and out of the building.
"It wouldn't be like visiting a construction site," he said. "We're obviously sensitive to the impact on our visitors. We want people to walk away feeling they've seen something neat."
Aquarium admission now costs $11.50 for adults; $8.75 for students, senior citizens and military, and $6.75 for children 3 to 11 years old. Younger children are free.
During construction, "we expect that the value of visiting the aquarium will not decrease," Mr. Pittenger said.
The source of the problem in the tanks, Mr. Pittenger said, is exactly what they're designed to hold: salt water. "You probably could not describe a more corrosive environment than sea water," he said.
The water seeps through flaws in the epoxy that coats the poured-concrete tanks and then eats into the concrete, causing tiny cracks.
"Ideally that coating would stay and be perfect for a hundred years, but I don't know of any tank in which the coating doesn't bubble. Every tank I've ever known has cracks in it. There is no serious structural problem in any of the tanks," Mr. Pittenger said.
The aquarium, designed by Cambridge Seven Associates, of Boston, was built by the Whiting-Turner Contracting Co., headed by Willard Hackerman. Mr. Pittenger said the building's problems could not be linked to the design or the construction work. The concrete, he added, met the specifications called for in the plans.
Over the last decade, new longer-wearing epoxies have been developed, Mr. Pittenger said, and the coating that will be applied to the tanks next year should last far longer than the epoxy that now coats the tanks.
"Ten years of service for that kind of coating on concrete -- I guess it's reasonable," he said. "But we hope we can do better."
Last year, Mr. Pittenger said, exterior and interior cracks in the building prompted aquarium officials to commission engineering studies to see if the structure was settling.
Those studies, which cost $250,000, showed "no major movement going on." But they did find deterioration in the ring tanks, which hold 600,000 to 700,000 gallons of water.
"What we see in the ring tanks is not serious," Mr. Pittenger said. "We don't have to get right in and repair. We have confidence those areas are in good shape."
Aquarium officials have not decided whether to shut both tanks down at the same time -- a more efficient method that might take a year -- or close them one after another, to allow visitors to see at least one of the tanks during construction, Mr. Pittenger said.
The work will include draining the tanks, chiseling out the corroded concrete, patching, replacing the epoxy, and repairing acrylic windows.
With the tanks drained, aquarium officials may decide to take the opportunity to replace some of the plumbing that makes up the life-support system for the marine life. Now, the tanks share a system. If the systems were independent, water temperature and other factors could be controlled separately, Mr. Pittenger said.
If officials decide to remove the 13-foot-high windows, a section of the roof will probably have to be removed to allow the panes to be lifted out, Mr. Pittenger said.
Officials at other aquariums agree that salt water damages concrete tanks. Rick Miller, public affairs manager for the New York Aquarium, said the work planned here "sounds pretty routine."
The New York building, opened at Coney Island in 1957, has undergone two complete renovations, he said. Recent repairs to corroding concrete in a 90,000-gallon shark tank cost about $200,000, Mr. Miller said. The aquarium charges $5.75 for adults and $2 for children.
At the 22-year-old New England Aquarium in Boston, designed by the same firm that created the Baltimore building, repairs and renovations are "routine," said Vikki Corlis. She said she could not recall repairs that required closing an exhibit for more than a few months.
The Boston aquarium charges $7.50 for adults, $6.50 for senior citizens and $3.50 for children 3 to 11 years old.