THA developed a phased Conservation Master Plan, after which the City embarked on a restoration program of the designated structures to address dramatic public safety issues. With the completion of each successive restoration project, selectively closed spaces were returned to public use.
Complexity of materials, building height, the scope of deterioration and the need for the site to remain open throughout construction presented unique challenges to completing the project. Roman stone, the precursor to precast concrete, had to be used in combination with natural sandstone. When THA began restoration, it was evident that the roman stone was extremely deteriorated. The architects were assisted by material scientists, engineers, the National Research Council, manufacturers and contractors in conducting archival research, followed by a two-year testing program to refine material formulae and manufacturing techniques for roman stone that could be used as a patching and casting material.