Chuck Pollock peered up the silo-like Oak Island Lighthouse and put his finger to a crack in the concrete exterior. It ran as far up as eyes could see.
The lighthouse’s interior bore the same affliction.
“Some of these cracks go all the way through,” Pollock, a Friends of Oak Island Lighthouse (FOIL) board member, said on site last Wednesday as engineers fiddled with gear that would help ascertain the problem’s severity.
Oak Island Lighthouse, the tri-colored concrete tower at Caswell Beach, has stood a half-century with only a single layer of skeletal rebar within its eight-inch-thick walls.
Inside the 140-foot-tall cylinder are top-to-bottom streams of runny, white lines, blaring indicators that moisture has invaded from the windy, salty beach environment.
With cracks in the concrete, there’s a chance the rebar may be corroded, which Pollock said could affect the lighthouse’s structural integrity.
“There are a lot of questions with this,” said E.B. Pannkuk, a structural engineer paged to the site last Wednesday. He works for Wilmington-based Andrew Consulting Engineers, which has designed or analyzed a number of concrete and historic structures in the area.
“It’s your lighthouse for the next day and a half,” Pollock told Pannkuk last Wednesday as his crew disappeared inside the structure with heavy equipment, one piece of which resembled a small cannon.
To put the building’s potential issues in perspective, Pannkuk said today’s standard would be 12-inch-thick walls and two layers of rebar, a web of steel bars reinforcing the structure.
Compare that, he said, to Oak Island Lighthouse’s eight inches and single layer. Then add the beach element.
“Think of a car parked at the beach all day,” he said. “You come back to it at the end of the day and there’s that residue on it.
“This thing,” he said, pointing to the lighthouse, “has been here more than 50 years” with daily whippings of salt wind. “The beach is just a very difficult environment.”
After a half-hour of prep came a shrill of heavy gear from inside the lighthouse’s reverberant base. Pollock and tour guide Bob Ahlers filed in for a look.
In the dark interior, lit only by a puffy sunglow from a small window, field technician Serge Stroehmer was boring into the wall with the cannon-like machine, a hollow-shaft drill a little more than three inches in diameter at the tip.
The bore was a meticulous process of dial-turning and sign language between Stroehmer and project manager Harry Slater as the screaming machine overruled any conversation.
Stroehmer withdrew the drill after several minutes, and Slater pulled from the wall a thick, stone rod roughly the size and look of a decorative candle.
Slater said the piece, bored out smooth as marble and containing rocks of various colors, would help Pannkuk determine the condition of the concrete.
The next step was a look at the rebar, which required another hole in the wall.
But on first impression, it didn’t look so bad, said Ahlers.
“There was just a very little bit of rust” on the exposed rebar, he said. “But we won’t know the extent until we get the report back, in a couple weeks.”
The report will examine the corrosion and the bore samples taken at various elevations in the lighthouse. Pannkuk pointed out that the tower’s three colors are not painted, but actually the color of concrete used. It was essential, he said, to look at each layer.
While the results are outstanding, “the fundamental structure remains sound and will continue to be open, in my opinion, for quite some time,” Pollock said. He added that with the rebar appearing about as healthy as hoped, the source of the weepy salt lines may be openings at the top of the lighthouse rather than cracks in its concrete.
Tours on tap
In the meantime, FOIL is readying the site for public tours available Wednesdays and Saturdays beginning May 26.
Ahlers added that he’s looking for volunteers — “no experience necessary” — to help FOIL’s efforts. Interested persons may e-mail lighthouse@caswellbeach.org for information.
Tour hours, requirements and other need-to-knows are available at http://oakislandlighthouse.org.
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