by Katherine Langdon
Since the summer of 2010, NCPTT has been actively researching the removal of crude oil from objects and sites of cultural significance, such as Fort Livingston. This 19th century coastal fort on Grand Terre Island, Louisiana, was badly contaminated by the 2010 Deepwater Horizon oil spill. Our scientists visited the site twice last year to perform some preliminary studies on oil removal, and this summer I have been continuing with research on removing weathered oil from historic brick. The goal is to find a cleaning method that effectively strips the oil from the masonry without causing additional harm to either the structure or the environment.
Historic brick is much more fragile than most modern brick because it was fired to a lower peak temperature, leaving it softer, more porous, and more prone to environmental damage than higher-fired, vitrified brick. Crude oil presents a triple threat to historic brick because it mars the appearance, traps moisture (encouraging mold and salt crystal growth), and contains acidic chemicals (and so will corrode lime mortar, which is basic). Thus it is important to find a way to remove the oil quickly and efficiently while keeping the following goals in mind: the cleaning method must not be acidic (i.e., it must have a pH of 7.0 or higher), must not leave a water-impermeable residue, and must not abrade or discolor the brick.
In the lab I am using historic bricks from Atlanta, Texas, which are similar to the bricks at Fort Livingston. These samples are soaked in salt water, coated in crude oil, and put through accelerated weathering to simulate the conditions of historic bricks along the coast. This week, the samples came out of the QUV accelerated weathering tester. I will begin the cleaning stage of the experiment to compare many products that meet our requirements. Recently we tested many of them on-site at Fort Livingston for comparison to the lab samples, and some of them did quite well! The final research and findings will be published on the NCPTT website in a couple of months.