Kriston Capps is a staff writer for CityLab covering housing, architecture, and politics. He previously worked as a senior editor for Architect magazine.
“We’re pushing the limits of what this material can do,” says a designer behind the Kennedy Center’s new building, describing its experimental concrete treatments.
The Reach, the long-anticipated expansion of D.C.’s John F. Kennedy Center for the Performing Arts, opened to audiences on September 7 with a festival featuring the Kronos Quartet, the Chuck Brown Band, Trombone Shorty, the National Symphony Orchestra, and many more artists. The building, designed to draw in new audiences with more intimate stages, played a key role in all those performances.
One of the design elements that visitors will likely notice right away is the “crinkle concrete” that lines the walls in several performance spaces. It’s a material developed by Steven Holl Architects specifically for the Kennedy Center expansion. For the Reach, the architects looked for ways to use concrete—acoustically and aesthetically—that haven’t been tried before.
Garrick Ambrose, a senior associate at Steven Holl Architects and project architect for the Reach, talked to CityLab about these novel applications of an ancient building material.
Can you explain the basic structure of the Reach?
The floors, the ceiling, the walls, the exterior facades are made out of cast-in-place concrete, which is a liquid material poured into forms that give you the final end product. The material goes from liquid state, hardens, and goes into a solid material state—that’s the actual structure of the building that holds everything up.
Why do some of the rooms at the Reach have different surfaces?
When you have two concrete parallel walls, like we do in our rehearsal spaces [Studios J, F, and K] and then in the Justice Forum [an intimate theater space], parallel walls are really bad for acoustics. You get a condition called flutter echo, where you have two sound waves bouncing off two parallel hard surfaces. So we had to break that sound up. What we needed to do was create a random texture which would diffuse and break up the sound. That’s where we came up with crinkled concrete.
So what exactly is crinkle concrete?
In our office, we took large, 10-by-4-foot sheets of aluminum that were thin enough to crinkle or fold by hand, but thick enough to hold that shape once it was crinkled. Once we had that form, we used spray foam insulation and sprayed the back of it, and that froze that form in place.
Once we had that, we sent that to Fitzgerald Formliners in California, and they made rubber casts of that aluminum foil that we crinkled. Fifty rubber molds were then sent back to Washington, D.C., and put into concrete formwork. Then we pour the concrete into the crinkle molds, then the molds are taken off, and you have the crinkle concrete exposed on the interior.
How did you know that this would get the acoustic performance you wanted to achieve?
There are two kinds of acoustical treatment. One is absorptive. You can do that through drapes, or with sound-absorbing materials like acoustical plaster. Then there are diffusing treatments, which are there to break up the sound so it doesn’t bounce back and forth.
We worked with an acoustician, David Harvey [from Harvey Marshall Berling Associates]. We knew that we needed to create a three-inch-deep texture in the concrete surface that would diffuse and break up the sound to mitigate the echo. We knew that the pattern needed to be as random as possible.
We experimented in our shop with different ways of getting that three-inch relief. When we stumbled upon crinkling the metal, we found that it was incredibly striking visually, and it gave us the random pattern needed, and it also gave us the three-inch depth to break up the sound.
The non-crinkly walls at the Reach have a specific texture, too. What is board-formed concrete?
When you get up close, from the imprints of the wood texture, you understand that the walls were originally built out of wooden strips. Then a liquid material was cast from those wooden walls. The forms give an imprint onto the final concrete walls.
That’s what the majority of the interior concrete walls are made of. That’s made from rough-cut, two-inch Douglas fir. We have the rough board form on the interior. On the exterior, the white pavilions, that is also Douglas fir. But that is a four-inch board, tongue and groove [a way to fit wood edges together to achieve a smooth surface]. That’s a more refined version of the board form you find on the inside.
Does this mean that you’re building a wooden structure with the same curving shape that you see in the final pavilions?
You almost have to build a building to make another building. It’s a building negative made out of wood to get the positive building out of concrete.
There’s another material in a studio ceiling that looks like a jagged blue sine-wave pattern.
That’s in Studio K. That’s also concrete. Studio K is the size of the [Kennedy Center] Opera House. That was the requirement. It’s a very large span. We also have the simulcast lawn above that. There’s a lot of load that goes onto that span. We came up with what we call a sawtooth post-tension bubble-deck slab.
Sawtooth post-tension bubble-deck slab??
The sawtooth shape [is] like mini beams that span across that space. Then we have post-tension cables inside the slab that are installed before the concrete is poured. Then we have bubbles, voids, inside that slab to reduce that weight. So it makes the concrete lighter, and it can span farther. That sawtooth is also a diffusive acoustical treatment on the ceiling. A flat ceiling, again, would bounce the sound around too much.
That [ceiling treatment] has never been done before, either. That’s an innovation. The whole building is made with concrete. It has a lot of acoustical requirements. We’re pushing the limits of what this material can do. We are pushing the limits geometrically with the swooping and curving forms and pushing it to perform acoustically as well.
How many kinds of concrete are in the Reach?
We have five different kinds of concrete treatment. We have a smooth board form, created with four-inch, tongue-and-groove Douglas fir board. We have a rough board-form interior, which is the two-inch Douglas fir board form. We have crinkle concrete. We actually have two types of crinkle concrete: One is white-stained, and one is left raw. We have smooth concrete on the canopies. Then we have terrazzo ground concrete on the floors.
What exactly does that mean?
Like you would sand a piece of wood, you’re sanding the concrete down, or grinding the concrete down, to expose the rock inside it. When you’re looking down, there’s a really striking pattern of all the stones that are ground with the cement. We selected blue stone as the aggregate. All concrete has an aggregate in it, which are small stones, which help give it its compressive strength. We used blue stone through the landscape, so we used blue stone in the aggregate for the cement mix and ground that. That’s the different stones you see in the ground floor.
Which of these materials was the hardest to develop?
The white concrete was very difficult. We wanted a color that complemented the white Carrara marble of the existing [Kennedy Center] building. White cement, which is typically what you use for white concrete, wasn’t quite white enough. So we needed to take white cement, mix it with white sand and light-color aggregate, and then add titanium oxide to really brighten up the mix. That was a very difficult process that took many mockups to perfect the bright color of the concrete.
It was also difficult to decide which type of wood we were going to use for the texture. We went through several different species of wood. We finally landed on Douglas fir and the four-inch tongue-and-groove board. It gave us a smooth texture. When you look at it from afar, there are no seams in the whole facade. It looks very monolithic and abstract. When you get close and touch the building, you see the imprint of the wood texture. It gave us that duality.
Why did Douglas fir work better than other trees?
Some other trees will stain the concrete or leave deposits in the concrete when the concrete was cast against them. You would leave the imprint of the wood texture but you wouldn’t get staining from the oils or saps that are in the wood. It also has a very nice grain to it, very straight and regular without a lot of knots.
Did you have many failures getting to the final results?
We did. That’s why the mockup process was incredibly important. We built mockups that were the size of a small room, testing all kinds of things, from the color to the texture. How to pour multiple pours, because you can’t pour the whole wall in one, so you have to test how you’re going to pour two pours or three pours to see what the joints between the pours are going to look like.
We had many failures that were actually important lessons for us. Each time we had a failure, we knew we had to correct something, tweak something, and get the mix perfect, and get the form work perfect, and get the work perfect, so that when we made the final pours—because you only get one shot, when you pour concrete, you pour it and then that’s it—we knew that we had to have all of our ducks in a row.
This interview has been edited and condensed for clarity.