An Elegant Structure of Rammed Earth

Tidal Resonance Chamber. Photo: Robert Horner

When artist-architect Robert Horner chose a building technique called “rammed earth” to create his Tidal Resonance Chamber, on Tacoma’s tideflats, he utilized a construction method that dates back thousands of years, to the Neolithic age. Yet the “earthen” chamber, a clean-lined trapezoid that harbors a 2,500-gallon tank of water pumped from the adjacent Thea Foss Waterway, is thoroughly modern in design – and it addresses contemporary concerns of ecology and sustainability.

The pool will eventually host barnacles and other aquatic life forms. Photo: Robert Horner

This permanent public art work is a contemplative space, one whose thick, freestanding walls offer a buffer from the industrial noise of the Port of Tacoma while allowing an open view of sky. The stone-filled pool ebbs and flows with the riverine tide via a series of feedback pumps. According to Horner, the chamber is designed to allow users to “synchronize with the natural rhythms of Commencement Bay,” and to “reflect on the manner in which human beings have utilized and manipulated the natural environment.”

Photo: Robert Horner

The former student of microbiology notes, “Estuaries have always fascinated me, especially how they serve as bio-filters for the planet.” Appropriately, the roughly 12′ x 18′ chamber is sited next to the Center for Urban Waters, a marine research facility housing the city’s Environmental Services Division, University of Washington Tacoma labs, and the Puget Sound Partnership.

Photo: Robert Horner

Tidal Resonance Chamber is Tacoma’s first construct from the rammed-earth method, a technique used in building the Alhambra, in Spain, and China’s Great Wall, as well as structures in the American southwest, where the material provides insulation from heat. Horner worked with builder Bly Windstorm of Port Townsend-based Earth Dwell LTD, which specializes in the eco-building technique. Historically, rammed earth construction has employed local materials and generated little waste.

Photo: Robert Horner

The chamber’s walls were constructed with a combination of local soils mixed with a small of amount of Portland cement, poured into staunch plywood/aluminum frames reinforced with rebar, then compressed (or “rammed”) every 6″ with a pneumatic tamper. The custom material, mixed with iron oxides, gives the walls their warm layers of color resembling sedimentary rock. After removal, the frames are reusable and recyclable.

How do ancient building techniques stand up to modern building codes? In an interview with the Tacoma News Tribune, city building inspector Jon Kendall said of the project, “I had never seen rammed earth before. But it tested at extremely high strength, around 6,000 psi. (City codes require at least 2,000 pounds per square inch.) It was a learning experience for all of us. Our biggest concern is that it’s durable – the cement content is pretty low, and we don’t know how it will stand up to the salt air down there. But we’re very satisfied. It’s a beautiful structure, though very labor-intensive.”

Ghostly trails of wind-driven salt trace the sides of the resonance chamber. “Windows” of water-filled glass tubes catch the sunlight (and reference the lab analysis taking place at the Center for Urban Waters, next door). Through a thin vertical opening, the Old City Hall clock tower is visible across the waterway. On a chilly winter day, the water is calm in the rectangular pool. Horner hopes that “it becomes populated with microorganisms and aquatic life. I think that process has already started….In a way, I think of it as a petri dish providing a [glimpse into] the dynamics of the Foss.”

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Center for Urban Waters. Photo: Jeff Barney

About the Center for Urban Waters: In addition to highlighting the city’s commitment to urban water quality, the facility, opened in 2010, is a showcase for sustainable building practices and energy conservation. The center is LEED Platinum-certified, the highest rating awarded under the LEED (Leadership in Energy and Environmental Design) rating system, the nationally recognized standard for green construction. Tours of the facility may be arranged at 253-591-5588; or

0 thoughts on “An Elegant Structure of Rammed Earth

  1. I had the great pleasure of working on this project with Robert Horner as it was my company, Earth Dwell Ltd., that constructed the rammed earth walls. While your blog captures the essence of the project very well I would like to clarify a couple of points. The soils used for the walls were carefully selected from nearby sources. A small amount of portland cement was added to the soil in addition to the iron oxide pigments that give the walls their rich colors. It is the cement that stabilizes the walls to resist the erosion typical of traditional clay based rammed earth and gives the walls a compressive strength greater than 7000 psi (concrete has a minimum compressive strength of 2500 psi). There was no chalk or lime added to the mix.

    The City of Tacoma, like many jurisdictions in the US, does not have rammed earth in their building code. Hence there was not a minimum strength required for rammed earth specified in the code. The engineering for the project required a minimum compressive strength for our walls of 2000 psi, which we exceeded by a factor of three.

    This project provided an opportunity for Tacoma to become familiar with the process of constructing rammed earth and to see that the walls are beautiful and strong.

    You may learn more about rammed earth at my

    Bly Windstorm

  2. Looking at how far we have come over the years is amazing. With southwest building construction in particular, things have come a long way. However, researching the options is still an invaluable first step with any construction project. McGraw Hill’s Southwest Construction site is a great resource for this. They have all the important information you need, including who is available for hire and what they are like, as well as what products and manufacturers are out there. Though I do work with them, they have honestly been a great help in all of my projects and have saved me both time and money.You should check them out.

  3. Rammed Earth mixed with cement should work, but in theory only last about 50 years with the decay of cement. There is a similar product going through testing at the moment called the mega block, which is a compessed block of eath by machine. This is very similar to what we see here in the tidal chamber. So far testing of the mega block looks very good.

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