Castillo de San Marcos & Fort Matanzas National Monuments

Project Sponsor: National Park Service (NPS)

Location: St. Augustine, Florida

Time period: 17th-19th centuries

Conservation: 2018-2021

Site History and Fieldwork

Castillo de San Marcos is a 17th-century Spanish masonry fort located in St. Augustine, Florida; Fort Matanzas is a solid coquina (shellstone) fortification built just south of St. Augustine. They were built while Florida was still under Spanish rule as a means to protect the town of St. Augustine from the attacks of other colonial powers. Over the centuries, the forts have been occupied by Spanish, English, and the US. The forts were retired in 1900, and in 1924 they were designated National Monuments.

The cast iron cannon at the forts range in size from 500 to nearly 8000 pounds, and date from the 17th to 19th centuries. Over the centuries, the salty coastal air caused the cannon to corrode, which would require more intervention to correct than simply cleaning the surfaces and applying a sealant. It would be too dangerous and expensive to establish a laboratory at either fort, so CRL staff traveled to St. Augustine to collect the cannons. The efforts to remove and, after conservation, replace the cannons from various levels of the forts required a custom-built chain hoist, a lull, a barge crane, and a lot of man power–in addition to staff from the CRL and NPS, we also had help from the St. Augustine Lighthouse and Maritime Museum.

Conservation Highlights

The CRL was hired to conserve a total of 25 iron cannons from the forts. The first step in conserving these cannons was to remove the thick layers of epoxy paint that they accumulated over the years. The CRL used a variety of methods to do this, including chemical peels, electrolytic baths, pressure washing, and of course, elbow grease.

All of the cannons were conserved using electrolysis, which you can read about in detail in our conservation manual, Methods of Conserving Underwater Archaeological Material Culture. In short, this process uses an electric current to remove salts and can reduce corrosion products back to iron. Some of the cannons needed extra work, as the bores were obstructed with concrete or cannon balls, which would have prevented us from treating the bores and can lead to problems in the future. Once treatment was complete, all of the cannons were sealed with matte alkyd paint; the first layer was pink and the next two layers black, so that when the black paint chipped away, it is easy to see, and staff can determine whether to re-apply the paint or consider re-conservation.