Tips from the Architect: In Situ Concrete

September 26, 2017

in situ: “In the original place. In the appropriate position” – Merriam Webster

In contemporary architectural practice, concrete walls are typically quarantined to buried underground locations as foundation walls or covered in gypsum wall board and plaster. Far from its apex of popularity and power in the Pantheon in Rome, concrete has suffered a turn of public opinion since the ‘Brutalist’ Movement of the 1950’s to 1970’s which featured concrete for its effect of massive presence. Boston is home to a few major monuments to the Brutalist Movement including City Hall (Kallmann and McKinnell), the Government Service Center (Paul Rudolph), the Boston Architectural College (Ashley, Myer & Associates). These buildings incorporate both precast and in situ concrete construction techniques.

There are some concrete buildings constructed almost exclusively out of in situ concrete. One exemplary building is Chapelle Notre Dame du Haut (Le Corbusier, France, 1950); Le Corbusier used a combination of both board-formed and Shotcrete (or Gunite). Both techniques yield drastically different finish textures, provide contrast between the roof and walls, and allow for highly irregular building forms. Shotcrete is the standard for pool construction, as it requires little formwork. Cement, sand and water are mixed continuously and sprayed onto a one-sided mold. This technique was used by Le Corbusier for both the walls and the roof. The walls were sprayed onto metal lath, creating an imperfect sprayed texture that collects the sunlight that streams through the wall and enhances its mystical nature. Roof construction involved spraying the Gunite against a curved board-formed mold. When the rough-sawn and knotted boards were removed, their natural texture left imprints on the concrete finish – preserved indefinitely.

Eero Saarinen employed similar techniques of board-formed concrete in his TWA Terminal (New York, 1962) and Ingalls Rink (Yale University, 1953). In both these buildings, Saarinen sought to capture the atmosphere of the experiences which the buildings housed. In the case of the TWA Terminal, he sought to capture the thrill of flying, while at the Ingalls Rink he sought to capture the excitement of the sport of hockey. To achieve his goal of creating exciting new forms, Saarinen employed the prowess of engineer Abba Tor who shaped the structural members and shells for the buildings. To construct the complex geometries of the buildings, they employed the technique of board forming – constructing the forms first of wood and then either spraying (TWA) or pouring (Ingalls) to create load bearing and spanning structures of concrete. In both cases, the concrete was left unfinished without any sort of plaster covering the ‘imperfections’ created by the construction process. In the case of the TWA Terminal, the complexity of creating the formwork for a doubly curved surface is exposed to this day. This construction technique is a testament to the planning and precision craftsmanship involved in its realization.