Earthy hues, heavenly structure
Colored concrete at the Los Angeles Cathedral
by Michael Chusid
common concrete has been uplifted into a structure that expresses the spiritual passions of its community. One of the most striking ingredients in this transformation has been the use of integral color in the concrete. Colored concrete was used to construct the cathedral and the adjacent bell tower and plaza, and is exposed as the finish for interior and exterior walls. Unlike the gray of typical concrete structures, the cathedral has an earthy golden cast that complements the Southern California sky and recalls the hue of the adobe used to build the first mission churches in the region.
 While the “mission adobe” palette harkens back to the past, the cathedral was also built with an eye towards the future. Dubbed the “Half-Millennium Cathedral,” the structure was designed to provide five hundred years of service to the Archdiocese of Los Angeles. This ambitious performance criterion figured in the decision to use integral colors since the iron oxide pigments that tint the concrete are permanent and fade-proof.
The colorants for the cathedral were supplied by Davis Colors, a brand of Rockwood Pigments and a world-wide leader in concrete color additives. According to Nick Paris, vice president of Davis Colors, “Iron oxides are the same pigments that give real adobe its buff tone and provide the color in such natural wonders as the Grand Canyon. The earth tones of the cathedral will last as long as the concrete itself.” The use of integrally colored concrete assures that the cathedral will be able to avoid the ongoing maintenance associated with paints and surface-applied coatings, he adds.
This is not to say that painted or prefinished surfaces were seriously considered on the project. The cathedral’s designer, Spanish architect Jose Rafael Moneo, envisioned the use of cast-in-place concrete from early in the project. His choice reflects his experience with architectural concrete in Europe and his concern for using materials honestly to express the character of the material from which a building is made. When another design option was proposed — to clad a steel frame with prefabricated panels — Moneo rejected the approach, stating that he wanted to “see the hand of the craftsman” in the construction materials. In keeping with the architect’s vision, the concrete shows subtle nuances in appearance due to the complex behavior of cementitious materials. “Concrete, whether colored or not, is a natural material prone to variation in appearance,” Paris says. Instead of being seen as defects, these variations are part of the aesthetic appeal of concrete, expressing its character and vitality.” Indeed, many visitors to the cathedral assume that it is made of quarried stone because the colored concrete has such a natural look.
The project team was faced with the challenges of designing a concrete mixture and establishing construction procedures to meet both the technical and aesthetic requirements of the building. The first large scale mock-ups built to investigate proposed concrete mixtures cracked due to heat produced by curing cement. The thick walls of the building, up to 60 inches in some locations, had created a heat sink that made it difficult for the cement’s heat of hydration to dissipate. Thermal cracking is not a problem in typical buildings. But in a monument designed to last five centuries, thermal cracks could allow corrosive chemicals to penetrate into the structure and lead to premature deterioration.
The conventional approach to this type of problem is to use cement and admixtures that release less heat. Such materials, however, were either not available from local suppliers or were too dark in color to produce the desired concrete shade. Another approach is to cool a structure by spraying it with water as it cures. However, this was unacceptable on the cathedral since concrete can pale if it is exposed to water before it has set sufficiently. To resolve these contradictory demands, a large number of additional mock-ups were constructed to test various concrete mixtures and techniques. |
Design approach
