researched the components used in Roman pozzolana, in order to achieve a similar reddish hue. Pozzolana additive was put in the mixture to soften its appearance and to make a symbolic connection through time to the origins of this composite material. He paid close attention to the forms, which were made of 3/4-inch exterior plywood, filled and sanded, and finished with coats of polyurethane resin. Thus, they can be used as many as eight times before being repaired and refinished. Kahn also decided to accentuate the joints between the panels instead of hiding them by chamfering the edges to produce a V-shaped groove at these points along the wall surface. Solid corners and gasketed joints were used between sets of gauged forms to avoid bleeding and leakage. The conical holes left by the form ties were also not patched, so their spacing were carefully placed, and they were filled by a lead plug, hammered tightly to prevent corrosion of the steel ties. Slate was chosen as the material for the courtyard because of its striking contrast with the concrete and its ability to convey the sombre dimension of an institution engaged in a constant struggle against life-threatening diseases. Later, the material was eliminated because of cost and replaced with travertine, which has similar symbolic connections. The travertine has not lasted as long as slate may have over time because of its relative softness, but has proven to be a perfect visual and tactile foil to the concrete walls. Teak was another material that was thought to be financially excessive at first, but Kahn decided to leave the material unvarnished and weather naturally to further reduce maintenance. Each decision in the design, such as mentioned above, has ensured longevity in an endeavor increasingly fraught with the risk of renovation or demolition....
