Summer School: Terra Cotta Details Will Live On at P.S. 173
SUPERSTRUCTURES typically prefers to replace defective terra cotta “in kind.” But in our current restoration of P.S. 173, a 1925 building in Washington Heights, terra cotta units are being replaced with cast stone.
For the school’s garland and baluster panels, the original terra cotta designs were laser scanned in the field using a handheld, 3D scanning unit—a process of about four hours. Next, the team post-processed the 3D data, checked against 2D images to verify scale, color, and other details. Once completed, the 3D data was converted into a digital model file (above).
The scan reproduced the existing panels with such accuracy that it even captured the imperfections of 100 years of weathering. The fabricator was requested to “patch” any losses to restore the panel to an “as new” condition, effectively reversing a century of damage.
This digital model guided a CNC router to produce the die shown above. Next, the die will be cast into a rubber mold for use in preparing the cast-stone replacement units. This process will retain a remarkable degree of detail from the original terra cotta to its cast stone replacement to ensure that the character of the building’s facade is maintained.
For non-landmarked buildings such as P.S. 173, cast stone offers an appropriate, efficient, and economical alternative. The material is a more cost-effective option and can typically be manufactured locally in a shorter time frame.