Performance testing of coatings for Sustainable Preservation of cannons and architectural elements at Fort Sumter National Monument

摘要

In 2008, a collaborative project between the National Park Service and the Warren Lasch Conservation Center (WLCC) of Clemson University was initiated to develop a protocol for conservation treatment of a selected set of ordnance and metal architectural elements located at Fort Sumter, a manmade island in the Charleston harbor, and Fort Moultrie, on Sullivan's Island, SC. One of the main objectives of the project has been to develop options for the National Park Service to allow for more sustainable and cost-effective management and maintenance of their items of cultural heritage. Extensive testing and comparison of different coating systems performance has been underway since 2010. 26 coating systems were applied to steel coupons with different surface preparation levels. Each steel coupon was painted in the laboratory prior to installation on an exposure rack on the dock at Fort Sumter. In addition, pull-tests were carried out on all coating systems included in the testing protocol. All coatings systems were applied to steel coupons with three different profiling types (none, steel-grit (to 3 mils), and subcritical fluids). This was done in order to compare the effects of the profiling on adhesion characteristics of the coating systems. National Park Service has allowed the WLCC to test these coating systems on historic artifacts in-situ at both Fort Sumter and Fort Moultrie. This rare opportunity allowed the WLCC to quantitatively assess coating performance on actual historic substrates with subsequent comparative studies being carried out on selected historic artifacts. The study focuses on assessing the performance of an oil-based alkyd system, previously selected by the park for their maintenance protocol, versus a modern coating system recommended by the industry. Two such comparative 'test stations' are currently in operation. Performance has been determined based on a qualitative and quantitative assessment of changes, defects and failures (if any), such as gloss, adhesion, cracking, delamination, corrosion, and loss of material. Findings of the performance testing protocol are reported and a cost-benefit analysis is utilized to discuss pertinent considerations for the cultural heritage field. Part of the results obtained from this extensive testing will be reported here, focusing mainly on the studies performed on the steel coupons subjected to a naturally corrosive marine coastal environment.