Fixing Fort Pulaski's Leaking Terreplein: Lead, Brick and Oyster Shell

Work on the terreplein in the 1930s. NPS photo.

What the terreplein is

At Fort Pulaski National Monument, the terreplein is the raised, grass-covered earth platform around the top of the fort, above the vaulted rooms called casemates. Beneath the earth lies an intricate drainage system:

• a layer of sheet lead laid over the casemate vaults;
• gutters running between the casemates, formed by brick arches built over the low point of each roof, where two vaults meet;
• oyster shell spread over the lead as a filter before the earth went on top.

An earlier repair

The Civilian Conservation Corps (CCC) and the Public Works Administration (PWA) dug up and repaired the terreplein in the 1930s: removing fill, having masons rebuild the latticed brickwork over the lead, repairing damaged abutment walls, and waterproofing.

Water damage in a casemate below a leaking stretch of the drainage system. NPS photo.

Why it needs repair now

For decades, water has seeped through punctures in the lead and into the casemates below. It has cracked the masonry and washed out mortar; mildew and lichens grow in the constantly wet spots, and the wooden casemate floors have rotted. If the original bricks loosen and the historic mortar keeps failing, the fort could lose historically significant material.

How it is being fixed

Five locations need to be dug up and repaired. The work is done by Park Service staff and members of the Traditional Trades Apprenticeship Program (TTAP), digging by hand and with an excavator up on the terreplein. At each spot:

1. The brick arch is taken apart, each brick labeled so the arch can be rebuilt exactly as it was, then removed and stacked.
2. The gutter is cleaned out and inspected to find the damage.
3. Damaged lead is removed, and failed mortar beneath it chiseled out.
4. In the casemate below, water-damaged mortar joints are chiseled out and the bricks cleaned.
5. The mortar is repaired, making a watertight seal.
6. The lead is repaired and the brick arch rebuilt.

The original loose oyster shell filter is replaced with bagged oyster shell.

Repairing the terreplein. NPS photo.

Sources

Based on "Fort Pulaski Terreplein Excavation," Fort Pulaski National Monument, National Park Service; a work of the United States government in the public domain. The source's "Civilian Conservation Corp" is corrected to Civilian Conservation Corps.