A brick and stucco lighthouse, built in 1811, stands on the southern point of North Island, a thirty minute boat ride off the coast of Georgetown, South Carolina. Today, after nearly two centuries of service, the lighthouse continues to be an important navigation aid for the shrimp boats and pleasure craft that travel out of Winyah Bay through the narrow channel between North Island and South Island. Despite many years of assault by sea air, wind, and rain, the historic lighthouse is in remarkably good condition.
During a routine inspection, in preparation for repainting, the Coast Guard found a few exterior cracks, areas of delaminated stucco and a handrail that needed to be replaced. They also identified a more serious condition that needed immediate attention. The brick and mortar foundation showed signs of deterioration caused by constant contact with salt water in the surrounding soil. Apparently, during storms, rain and salt spray would pelt the lighthouse and run down the sides, permeate the sandy topsoil and accumulate next to the foundation.
To stop the deterioration of the foundation, the Coast Guard engineers specified a technique called "curtain wall grouting." This involves injecting a polyurethane grout completely around the structure to create a waterproof barrier. The specifications for this project called for injecting Prime-Flex 910 through soil probes driven thirty inches into the ground, spaced thirty inches apart.
The Coast Guard contracted with Brantley Construction Company of Charleston to repair and repaint the lighthouse. General Materials, Inc. in Charleston supplied the necessary repair materials.
Prime Resins sent Randy Brooks to the job-site to provide technical installation assistance. When injection started, Randy noticed that the specified thirty-inch depth for the soil probes was too shallow to allow sufficient horizontal migration of the grout. Most of the grout was following the path of least resistance upward through the drier sand, and alongside the probe pipe. It also became apparent that the specified distance between the probes was too great for the grout from one probe to migrate across to the grout from the previous probe. To insure a good watertight curtain, Randy recommended changing the depth to five and one-half feet and the distance between probes to eighteen inches.
To stop the grout from flowing back up alongside probe pipe, Randy suggested that at each new probe, the crew start by injecting a small amount of Prime-Flex 910 with 5% catalyst and then wait about 90 seconds. While they waited, the grout traveled up a short distance alongside the probe pipe, cured, and created a gasket around the pipe. When they resumed injection, this gasket forced the rest of the grout to migrate outward into the surrounding soil. To insure complete protection, Randy recommended that they repeat the process with the injection probes midway between the first set of probes.
General Materials supplied Prime Bond 3100 and Prime Gel 2000 to complete the other repairs. These products were used to repair the cracks and reattach the delaminated stucco.
Because the lighthouse is only accessible by boat, the Brantley work crew stayed on the island during the project. The accommodations were primitive--thirty year old bunkhouses with no running water. The only other residents on the island were deer and wild boar. The deer were protected, but the wild boar were fair game. One evening, a member of the crew left the bunkhouse to heed the call of nature and was confronted by a huge male boar. After recovering from fright, he shot the boar. The crew reported that wild pig, properly prepared, can be pretty tasty.
