Evaluation of Cleaning Methods for the Exterior Brick Atthe Brooklyn Historical Society

The Brooklyn Historical Society's headquarters, designed by George B. Post, was constructed in 1881. This ornate brick and terracotta building is a landmark in downtown Brooklyn, New York. The building has never been cleaned or repointed. Heavy accumulations of black particulate soiling are present on both brick and terracotta. Many mortar joints are either failing or are completely without mortar. Recently, the Historical Society decided to develop a program for cleaning and repointing the exterior masonry. The project-specific difficulties in cleaning the brick can be attributed to the highly absorptive nature of the brick and the unusually high percentage of sulfates (caused by the use of a gypsum-gauged mortar in the original construction) within the brick. A sequence of site and laboratory analyses was performed to determine an appropriate method of cleaning that would not cause damage to the brick and would not increase the risk of future damage to the brick from salt migration.