Interior Rammed Earth Panels - Thinner Prefab Panels And A Cool Blue Hue

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Reformation says their clothing is the most sustainable option next to being naked. Little wonder that when Reformation opened their new store on Melrose Avenue in Beverly Hills, they decorated it with a rammed earth wall and next to nothing else. The interior of the store, designed by Montalba Architects, with construction completed by Shawmut Construction, is as spare and refined as the clothes on the racks. Image © Jesse Gillan

In our last two posts we wrote about the lobby walls at American AgCredit and Stadium TechCenter. They begin to tell the story of an exciting new use for rammed earth - a game changer for the material. For millennia, rammed earth has been massively thick and monstrously heavy - big wide walls intended to support roofs and to keep out weather and invading marauders. Today, with space at a premium, thick walls take away valuable real estate and square footage from the building. Constructing them on site is complicated, time-consuming and expensive. New energy standards enacted in the 2016 building code require that rammed earth walls be insulated, making them even more expensive. How many times have I seen the line item “rammed earth walls” get eliminated from a project during final budget crunching? 

Not anymore. Not since we figured out how to slim down. For the past two years we’ve been refining a technology to manufacture rammed earth in thin panels, suitable for shipping to a job site for use as exterior cladding or interior finish. It hasn’t been exactly smooth sailing because the forms, delivery, extraction, storage, trimming, transport and installation all had to be either modified from existing technology or invented from scratch. 

Early on in the process we found out that the forces exerted against the formwork from compacting thin walls were much higher than what we saw compacting the more traditional 18” thick walls. We learned this by watching what was supposed to be a three inch thick wall stretch to four inches thick as the formwork bowed under 10,000 pounds per square foot of force. To counter this tendency for the panels to expand under the force of compaction, we braced our forms with high strength tube steel, hydraulic jacks and steel plates bolted to the concrete floor. 

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Pre-cast interior rammed earth panels being delivered to the new Reformation store in the Mission district of San Francisco. To accomplish the delivery - which had to be made through the storefront's narrow front door with no room for a forklift or crane - we built a portable jib to transfer each 2,000 pound panel from the trailer to the sidewalk and we built a six-wheeled trolley to roll the panels into the store. As you can see, it took three people pushing and one pulling to get the panel up and over the door threshold. The rammed earth arrived safe and ready for installation in a retail store that could have never used the material with traditional on-site form setting methods.

We designed a C-channel trolley with thirty-six caster wheels to roll the four thousand pound panels out of the formwork, used an overhead crane to lift the panels off of the trolley and onto a curing rack, designed a cutting table with a sliding slab saw like a library ladder to cut the cured panels to exact dimension, and fabricated custom steel frames to use for lifting and mounting the cast, cured and cut panels.

And then there was that time when a neat stack of six beautiful twenty-four foot long panels fell over like a stack of dominos and smashed themselves on the cure room floor. That disaster motivated a complete make over on the curing rack concept.

Long story short, we knew from that first experience with our precast rammed earth walls for Stadium TechCenter that thin panels had a future. All we had to do was solve a mountain of new challenges. But thanks to that first use of transportable panels we were introduced to a few trusting and adventurous clients who gave us the incentive to tackle these challenges.

One of these early clients was Reformation - a retail clothing store with the tagline “being naked is the #1 most sustainable option. Reformation is #2. Reformation was opening new stores in San Francisco, Los Angeles and New York. For the first store in San Francisco’s Mission District, they hired Bohlin Cywinski Jackson architects, known for their cutting edge design of the Apple store in midtown Manhattan. BCJ approached us about installing a group of precast panels of rammed earth as a focal point in the Mission District Store, despite the fact that a free standing installation such as they proposed had never been done before.

Having recently finished our installation of the 400 square foot, 28,000 pound Stadium TechCenter rammed earth project, we felt pretty confident telling Reformation that we could design, manufacture and install 100 square feet of rammed earth walls inside of a renovated building in downtown San Francisco. No matter we hadn’t quite solved the problems we would encounter offloading panels on Mission Street, rolling them along a sidewalk jam packed with pedestrians, squeezing them through a five foot wide front door with a sloping threshold, and then hoisting them into place onto the supporting steel columns. 

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Pre-cast thin interior rammed earth panel at the Reformation store in Los Angeles. After curing in the shop for a month, each of the panels was cut in half to facilitate transport, then re-assembled in the store and mounted onto a square tube steel frame bolted to footings beneath the original concrete slab floor. The “end grain” of the cut panels reveals the small stones and gravel that are a component of the formulations that give each layer its strength and color. Image © Jesse Gillan

What was most challenging in getting to the finish for Reformation wasn’t as much the technology as it was the color pallet Bohlin Cywinski Jackson and the owner wanted us to achieve. They didn’t want the beige and brown most people associate with earth. They wanted grays and blues - harder to find in the wild. We looked for blue rock everywhere from Monterey County in the south to Humboldt County in the north, and way out east to Amador County. The bluest granite we could find was in Watsonville, 138 miles south of our shop - a long distance to haul sand and gravel, but since the panels were only three inches thick, we got by with one ten-wheeler load. The formula itself used the Watsonville blue granite, Byron yellow silt as a filler, and Riverside white cement as the binder. To get the gray color Reformation wanted, we had two different formulas - the Watsonville blue granite with Portland cement, and our local Mark West Springs basalt with Portland cement. As you can see in the photos, there is a subtle difference between these two grays.

One of the most strongly held principles we have for our work is that the rammed earth walls we build must derive their color from the minerals that occur naturally in the clay, sand and gravel we use in our formulations. While many other rammed earth installers rely on processed pigments to color rammed earth walls, we think it is a key part of the sustainability message that the aesthetics of a wall are true to the geologic formations that produced the raw materials themselves. Gray and gold granites, tan and brown volcanics, red and yellow sedimentary, white, black, blues and even green serpentine. 

All these colors were laid down by nature millions of years ago in epoch after epoch, and in our work we strive to create walls that celebrate the processes of geologic lithification. Using manufactured pigments as a way to add color to a rammed earth wall just doesn’t duplicate nature. The colors are oversaturated and (can I say?) unnatural - see this, this and this for examples of what we’re working to avoid. For some reason that is still a mystery to me, rammed earth using artificial dyes is too often getting incorporated into walls that can look like a barber pole - stripes of brown and red that don’t look even remotely like John Wesley Harding’s trip down the Colorado River or the thousands of road cuts across the United States exposing the wonders of natural rock.

I mentioned earlier that it wasn’t producing these panels that was challenging, but rather getting them into the store and onto their supports. For those of you who read the Stadium TechCenter blog, you’ll remember I made a big deal out of how tricky it was to get our long panels into the lobby and up onto the wall. The panels for Reformation were shorter and lighter, but access was more difficult. 914 Valencia Street is the heart of the Mission District, which means a lot of traffic, both pedestrian and vehicular. There was a left turn lane in the middle of the street where some delivery trucks stopped, but getting permission to cross Valencia street in mid day with a forklift was a non-starter. We decided to build a jib crane that would mount to a portable stanchion we could set up on the sidewalk. We used a chain hoist on a slider to lift the panels one at a time off of our low boy trailer and set them on a six wheeled trolley (think extra long skateboard) we built that could carry the two thousand pound panels. It took four strong men - two pushing and two pulling - to roll the panels along the sidewalk, up the ramp, and over the door threshold. We positioned the trolley alongside the steel supports, used the chain hoist again, and eased the four panels into their final resting spot - the first thing you see when you walk in the store.

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 The interior of newest Reformation store, located a few blocks east of Beverly Hills, features a 200 square foot free-standing mural of stratified rammed earth floating above a polished reclaimed concrete slab - nearly naked.  These thin slabs of rammed earth are like nothing else. Everywhere in the world, rammed earth walls are thick, massively heavy, and constructed right at their final resting place. Making rammed earth thin enough to put on a truck, carry into a building, and hang on a wall is a paradigm shift for the earth building industry.  Image © Jesse Gillan

BCJ was right. The blues and grays look good, and the thin panels were the only way they could have used rammed earth in the store. Creating subtle color changes in a rammed earth wall isn’t easy, but we’ve been working on it for a long time ... and feel good about where we are. The fact that we are seeing so much interest from architects and interior designers about the thin panels is great. It will create so many more opportunities to showcase the beauty of building with earth.

I was going to end this blog right here, with completion of the Reformation store in San Francisco, but while waiting for permission to post it and for the professional photographs by Matthew Millman that would accompany it, we had a chance to install a second panel collection, this one in the Reformation store at 8000 Melrose Avenue in Los Angeles. We used the same color pallet as the Valencia Street store, but assembled the panels into a wall that was twenty four feet long and eight feet tall - over twice as big as the previous installation. Lucky for us we didn’t have to unload on busy Melrose Avenue as there was a back door to the store and a parking lot, but rolling each of the four 2,000 pound panels into place wasn’t any less challenging. 

We used a nearly identical mounting detail as Valencia Street - steel frames on the back of our panels, bolted to steel columns set in concrete footings - and lifted the panels off of the trolley into place with a chain hoist mounted to the ceiling joists. Also, like Valencia Street, the panels are supported on a steel 4” x 4” angle iron to visually lift them off of the concrete slab floor and to protect the bottoms of the wall from accidental damage from mop buckets and baby strollers. 

We are very grateful to the visionaries behind the Reformation mission for giving us the chance to showcase this exciting new slimmed down rammed earth. As we continue to refine the methods that allow us to build and install thin panels, we see countless opportunities for their use. As I wrote at the beginning of this blog, as awe inspiring as monolithic rammed earth can be, there are just so many obstacles being thrown in the way - codes and crowded job sites being two of them. By making rammed earth thin and portable it’s now possible for architects to bring the beauty of rammed earth to projects formerly off limits.
 

Rammed Earth Slims Down - Pre-Cast Rammed Earth Responds To The Modern Built Environment

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The new rammed earth, slimmed down and ready for the show, complements the palette of crisp, modern finishes in the lobby of the six-story Stadium TechCenter in Santa Clara, California. Interior design by SmithGroupJJR.

For thousands of years, rammed earth has been a hallmark of sustainable construction - thick insulating walls made from rock and earth sourced from the building site itself, or just nearby. Rammed earth has gone through a renaissance of sorts over the past 30 years with the craft being celebrated and appreciated by modern architects. But beyond refining the technique and making it conform to modern building codes, not a lot has changed - rammed earth walls are typically thick, insulating, load bearing and exterior.

Now, interior designers and architects are looking for the beauty of rammed earth without the bulk. How can rammed earth continue to modernize in the face of ever evolving construction techniques? Big buildings are made of glass and steel, insulation standards have mandated a certain type of interior-exterior separation, and more important than anything, cost and speed of construction are relegating traditional rammed earth back into the past. But what if there were a different way of adapting rammed earth to our modern era?

I remember the first meeting with the architects at the SmithGroupJJR in San Francisco. I was there with Khyber, our most experienced rammed earth installer, and Dan, our project coordinator. SmithGroup had been awarded the contract to design the lobby for the new Stadium TechCenter in Santa Clara, and they wanted to push the envelope with an exciting, sustainable, new design concept. How much further could you push interior design than hanging a 30,000 pound mural made of compacted earth on the wall behind the reception desk? Dan, Khyber, and I stole glances at each other, knowing that if I said “yes” we were committing ourselves to something that had never been done before. 

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Depending on the epoch and the thousand year floods, nature can lithify layers of sedimentary rock that are deep and highly contrasting, or pencil thin. It can take a million years to build a rock five feet thick.

Our last project that called for a lobby feature wall - the American AgCredit building - was designed around a more traditional, thick monolithic rammed earth wall. The construction process gave us some limited room to build the interior wall while the rest of the building’s steel structure was assembled around it. But in this case, the Stadium TechCenter already had the steel superstructure and intermediate floors in place. There was no way the owner was going to let us bring formwork into the lobby and make all the mess and noise associated with classic cast in place rammed earth, not to mention how much this would disrupt the schedule. No, we’d have to figure out a way to make the wall off site and transport it to Santa Clara. Simply put, we’d have to bring the mountain to Mohammed.

How could we manufacture long pieces of rammed earth thin and light enough to transport, yet strong and stiff enough to survive the bumps along the road? Could we engineer an assembly to mount thin wall panels two stories high onto a structural back wall, and would they stay there in a big California earthquake? 

What was the biggest challenge? Making a relatively thin rammed earth wall at our shop? No, we’ve been building thin mock-ups for years as samples. Picking the wall up and loading it on a truck? No, we’ve delivered mock-ups to clients multiple times. Making a wall out of many different layers and colors? No, we’d just done this for American AgCredit. The challenge here was the scale and the complexity of the operation. 

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The safest way to transport and mount the big panels was to support them in a steel frame, with lifting hooks welded to the frame. Notice the subtle changes in strata and color patterns between these two panels.

The wall in the lobby for the Stadium TechCenter was going to be twenty feet tall and twenty-two feet long. We’d have to make four individual long panels, each panel five feet high and 6 inches thick. At 136 pounds per cubic foot, weight was going to be an issue. How were we going to get these long, thin panels onto a truck, drive them sixty miles, get them off the truck, and then squeeze through a front door barely wider than the panels were long? (Don’t make the mistake of thinking we could turn them sideways to get through the door because we couldn’t). Once inside the lobby we had to stack them one on top of another up to the full twenty feet, and look out! The already-installed fire sprinkler pipes were only twenty-one feet off the floor.

OK, back at the shop. We designed a steel frame made from five inch angle iron and flat bar with intermediate rebar. The idea was that we would have a rammed earth wall built within a hidden steel frame - stiff enough to transport without breaking and strong enough to mount onto the wall at the Stadium TechCenter. We welded temporary hooks onto the frame so we could lift the panels up once they were fully cured. We made one frame for each panel, and used our standard rammed earth forms to encase the frames while ramming. The forms were reusable. 

Relatively straightforward so far. We had a lot of color work and small sample walls to study before we satisfied the architects on what the wall was going to look like, but once we had our formulas - there were six different mix designs - the real work of mixing and compacting could begin. It is much more complicated to create a wall of multiple colors and variable lift depth than a monochromatic wall of uniform lifts. Each mix pile was labeled and the equipment operators had written instructions on when to change colors. Khyber had his list of lift heights and where to introduce the infusion lines. And remember, each of the four panels was a different combination of color and strata to create the overall composition of the mural. This was definitely not a blow and go type of install. It’s more like painting a watercolor landscape while wearing a blindfold. 

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For the installation of the four big Stadium TechCenter panels, we used a long reach forklift to set the panels rather than a crane because the roof was already on the building. The forklift picked each of the five foot high panels off the truck, backed directly into the lobby with only inches to clear the door frames, executed a ninety-degree turn and placed the panels one on top of another against four steel posts where they were welded in place.

The panels within their encased steel frames cured at the shop for a month before it was time to deliver them to job site in Santa Clara. We wanted to be confident that we could pull it off, so we went through a practice run at the shop, picking up one of the panels and placing it on top of a lower one. On the job, we had to coordinate timing and installation carefully with the project supervisor because there were dozens of other trades working there, and pretty much everybody was in each other’s space. We needed the front of the building to park our forty-foot delivery truck so we could off-load our panels and get them through the front door (which as I pointed out was only one foot wider than our panels). 

We used a high reach forklift to pick each panel off the truck, back directly in through this narrow opening, rotate ninety degrees, and then slowly drive the panel forward until the backside made contact with the steel columns that would support the group of four stacked panels. The forklift held each panel in place while the flat bar was permanently welded to the columns. The assembly was a nail biter, but I’m happy to say it went off without a hitch. Dare I say, “almost like we planned it.”

Thirty thousand pounds of stratified rammed earth mounted on the wall in Santa Clara is a good feeling for us. Massive rammed earth walls, built the old way, take up prime space in the building and valuable time in the construction scheduling. Simply speaking, there are many projects where classic rammed earth is just not practical. Slimming down has opened a lot of new doors. Whether it’s an art piece on the wall or a rainscreen cladding, rammed earth has a bright and bold new future.

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Twenty feet tall and six inches thick, the “mural” of stratified rammed earth mirrors the geological diversity of California’s Coast Mountain Range, and celebrates the diversity of California’s multi-ethnicity. Image © Michael David Rose

Building A Rammed Earth Lobby Wall For American AgCredit - The First Of A New Journey

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The first thing you see walking into the new headquarters for American AgCredit is the rammed earth wall, built with different strata representing the diversity of soils in the regions served by this bank for farmers. The wall itself is forty feet long, twelve feet tall, sixteen inches thick and weighs roughly 84,000 pounds. The entire project, designed by TLCD Architects and built by Jim Murphy Associates, comprises 120,000 square feet of sustainability and energy efficiency driven features.

It all started with a request from American AgCredit for a monumental rammed earth lobby wall that would express the relationship between agriculture and art. In October of 2013, this letter came into our office from Don Tomasi, Principle at TLCD Architecture in Santa Rosa, California:

I am the Principal-in-Charge for my firm for a new headquarters office building for American AgCredit, to be located in the Airport Business Park north of Santa Rosa. I am considering proposing a rammed earth wall at the main building entry, behind the reception desk. There is a potentially intriguing link between between my client's agricultural mission and an earthen wall, and I'd like to explore the possibilities with your firm if you are interested. 

My answer to Don, “Am I ever interested!”, but little did I know in October of 2013 where saying yes to TLCD, AgCredit, and an art wall adorning the reception area of an office tower was going to lead us.

Building a forty-foot long, twelve foot tall, 16” thick stabilized rammed earth wall comprised of multiple soil types is relatively straightforward for our team. After all, we have been building much bigger and more complicated wall systems for years. Our site-assembled and crane-set forming protocols are well established, as are volumetric mixing, conveyor delivery, and pneumatic compaction. In fact, we’re quite proud of all the cool things we’ve invented and built over the years that allow us to control consistency and wall quality on projects even larger than this one. 

I especially liked the idea of building a wall for American AgCredit, a bank whose sole mission is lending money to farmers. All of us at Rammed Earth Works appreciated the link between growing crops in earth and building a wall of earth in the lobby. The owners wanted us to incorporate soil from all of the regions served by the bank into the wall - Kansas, Oklahoma, Colorado, and across California. This wasn’t exactly practical, given the long hauls and budget constraints, but I did see how it was symbolic of the diversity of soil and agriculture. 

OK, so they wanted a rammed earth wall made up of multiple soil types, each yielding a different color and a slightly different texture. The wall was going to represent the reach of AgCredit, but we needed to create the pallet using soils that were close to the project site. Our color lab has gotten really good at developing mix designs from site soil and quarry crushings that conform to an architect’s color preferences, and by altering particle size gradations we can change the surface texture. I felt pretty safe saying we could meet their expectations on color and strata. 

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The challenge for us in building the forty-ton rammed earth wall for American AgCredit was the fact that it was supposed to end up in the lobby. Because installing a traditional rammed earth wall requires a lot of space and equipment, we had to negotiate with the contractor to let us be one of the first subs on the site. The big footings that would be supporting the 2.8 million pounds of structural steel and 51,000 square feet of glass were the only part of the construction in our way when we set up.

It took us quite a few variations of samples and mockups to satisfy their aesthetic and symbolic criteria. We pulled materials from five different quarries - Calistoga, Santa Cruz, Glen Ellen, Byron, Napa, and a little red clay from Calaveras County - and three types of cement.

Estimating the materials and labor to actually build the wall? No problem. 600 square feet of double-sided formwork; 40 cubic yards of blended aggregate; 8.5% binder; two weeks to set forms, five days to ram, three days to strip and clean up; single mobilization, one or two call backs. 

But here’s the catch. Our wall was going to be in the center of a 120,000 square foot structure, surrounded by steel columns and concrete beams. In order for this to work we had to negotiate with the General Contractor to let us build our wall before any other structure was erected on the site. The GC agreed, so long as we would protect the wall from damage over the following two years of construction schedule. He squeezed us into the Gantt chart between footings and superstructure, which turned out to be not just a narrow window in time, but a window in space as well. They agreed to hold off on the steel frame until we were done, but they couldn’t hold off on digging footings. You may not realize how big a footing is for an office tower, but let me just say that it’s too big to step over, or to drive a bobcat or a high reach forklift over. Yes we had our little island in the center of the site to set our forms and build our wall, but getting to this island was a logistical nightmare. Everything took extra time, bridging, and required
equipment with a longer reach.

Long story short, we built the wall, they finished the building, it opened in March 2016 and went on to receive the 2016 AIA Redwood Empire Citation Award and the North Bay’s Top Projects Award. The building exceeds U.S. Green Building Council LEED requirements for Gold-level certification. Our rammed earth wall is the first thing you see stepping in the lobby.

What we learned:

1. Building really cool rammed earth walls for display in high traffic commercial and retail spaces is a great way to showcase our work.
2. Building really heavy rammed earth walls inside of another structure is complicated. Based on the success of the American AgCredit building, we knew that one day soon we were going to be asked to do another wall in a lobby, and when it happened, we needed to find a better way.

That day came sooner than we thought. In November of 2015, I received this letter from Justin Hughes of the SmithGroup:

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Setting forms, and then filling them with all of the different soil layers, took only a few weeks. After our forms came down, however, we had to build a protective wall that remained in place for over two years while the building was finished, which meant we had to wait two years for everyone to see what it was we had accomplished. 

Hello,
 
My name is Justin Hughes, and I’m an architect with SmithGroupJJR in San Francisco. We have just won a project to design a lobby for an office building in Santa Clara. We would like to use rammed earth as a 2-story feature wall as well as a floor material. We would like to discuss this with you, hear about your experience, understand some of the detailing as well as the possibilities and limitations of the material. The sooner we can meet, the better. If possible, we would love to have a meeting with your representatives and our project team in our office early next week, preferably Monday or Tuesday.

So here it was. The chance to innovate a whole new system - precast rammed earth. How could we manufacture big pieces of rammed earth thin and light enough to transport, yet strong and stiff enough to survive the bumps along the road? Could we engineer an assembly to mount these wall panels two stories high onto a structural back wall and would they stay there in a big California earthquake?

I said yes to Justin Hughes. I had to tell him we hadn’t done it before, but I knew figuring it out was going to be fun. I’ll tell you about it in the next few weeks.

Dwell Magazine Special Issue Materials Sourcebook Features Rammed Earth Works

Dwell Magazine included Rammed Earth Works (as well as Watershed Materials) in their recent Special Issue - Materials Sourcebook 2016. We're so honored!

The letter from the Editor-in-Chief, Amanda Dameron, entitled In the Material World speaks to our mission in more ways than one :

"Over the past 16 years, we've amassed a deep archive of architectural projects that convey modern values through conscious design decisions. This special issue celebrates the way that architects and residents alike have engaged bold material palettes as a vehicle for communicating their ideals.

In the pages that follow, we honor the artistry of the build through the lens of material exploration. We acknowledge that when architects experiment with material properties, they push their own power of expression.

While the wheel need not be reinvented with each use of stone, wood, concrete, metal, glass, and even recycled goods - surely we can chart modern architectural progress through technological innovation and ceaseless iteration. What would 'modern architecture' mean today if Alvar Aalto hadn't spent years experimenting with wood, if Louis Kahn hadn't embraced brick, or if Frank Gehry hadn't explored the limits of metal?

It's inconceivable to conjure the work without the materials, not to mention the tireless minds that dared to recast the mundane."

We couldn't agree more!

This feature is a reissue of a larger Dwell Magazine story on Rammed Earth Worksoriginally published in April, 2009.

Open House - Saturday February 13th 2016

Rammed Earth Works and Watershed Materials are hosting an Open House on Saturday, February 13th from 10am to 3pm at our production shop / pilot factory / research lab. RSVP on the Facebook event page. Stop by to get an in-person tour of :

- Rammed Earth Works' curved demonstration wall designed by Andy Goldsworthy

- Pre-cast rammed earth

- Watershed Materials' new prototype high compression concrete block machine

- Zero cement block mix design made with lime, slag and aluminosilicates

- Zero cement geopolymer block

- Black block made with rice husk ash

If you're attending the BuildWell conference, this is a perfect finale. Our factory is located at 11 Basalt Road, Napa CA 94558. Call (707) 224-2532 if you need help finding the shop.

Pre-Cast Rammed Earth

The Rammed Earth Works team has been ramping up production of our pre-cast rammed earth panels, made in our factory in Napa then transported to and installed on job sites.

These pre-cast rammed earth panels are 3-4 inches thick and are ideal for non-structural applications for projects that don't have the available footprint for traditional on-site rammed earth walls that can often range from 18-24 inches thick. Rammed Earth Works is able to produce these panels at our factory at much higher volume than on-site installations with custom one-off formwork. Rammed Earth Works is able to take advantage of re-using formwork as well as the factory environment to speed production time.

Measuring five feet high by twenty-four feet long, each of the 3” thick panels weighs 4,200 pounds when fresh out of the mold - 3,850 once the hydration water is converted. What keeps them together? Ultra high compression.

Working with panels this thin, delivering the soil mix into the formwork at a uniform depth is essential. The team at Rammed Earth Works continues to develop equipment specifically suited to the task at hand. Here we’re using a linear traveling delivery conveyor dropping mix through the feeding box - three linear feet every fifteen seconds; 2.4 cubic feet per lift.

Each five-inch loose lift takes one minute twenty seconds to deposit into the formwork. Target density is 136 pounds per cubic foot. A Jet 2-T rammer has a tool weight of twenty-one pounds, works on 90 psi of air pressure, and has a strike rate of 700 blows per minute. To reach 97% compaction rate, the rammer travels along the twenty-four foot long wall at the same rate as the delivery conveyor - three linear feet every fifteen seconds.

Here's an installation of pre-cast rammed earth panels at a job site in the South Bay Area. We look forward to producing more pre-cast rammed earth and reporting back on the progress.

BuildWell Conference 2016

Are you attending BuildWell 2016? We're excited to be involved in our second BuildWell conference. This year, David Easton will be speaking in two panels:

Ultra Low Carbon Materials : Natural building goes mainstream from 11:15a to 12:30p on Wednesday, February 10 

Going Big League : getting to scale - the good, the bad, and the ugly from 11:15a to 12:30p on Friday, February 12

We're also hosting an Open House following the BuildWell conference at our shop / factory / research lab in Napa - a great way to end a week discussing the future of sustainable building materials.

Rammed Earth, A Historical Perspective And a Solution to Modern Day Challenges

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Vernacular rammed earth structures common in China.

The following is a guest post by Dr. Rongrong Hu, professor at Xi'an University of Architecture + Technology and an expert on rammed earth in China. She visited Rammed Earth Works and gave a talk at the Hamel Winery called “Rammed Earth, A Historical Perspective And a Solution to Modern Day Challenges”. We enjoyed her visit, learned tremendously from her international experience, and are proud to share the report of her trip :

When I step on the thousand year old Great Wall of China built with rammed earth or when I see the old and beautiful vernacular rammed earth houses in China, a question about rammed earth construction always comes to my mind: what is the future of this disappearing ancient construction technique with such a long history in China?

To help me find the answers, David Easton, founder of Watershed Materials and Rammed Earth Works arranged a trip to Napa where his companies are headquartered. Arguably, Napa is California’s rammed earth country. Going to Napa, I really did not know what to expect. I knew David is very passionate about rammed earth construction, after all he has devoted most of his career to this technology and specifically to creating a new construction block made with technology that evolved from rammed earth. However, I did not know I was about to meet so many enthusiastic people from different walks of life, all with the common goal of furthering the progress of this technology.

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Dr. Rongrong Hu and David Easton at the Watershed Materials headquarters, standing in front of a building made with rammed earth Watershed Block below rammed earth PISE.

I drove to Napa valley on Saturday, August 21st. Arriving early afternoon, first on the agenda was a tour of David’s extensive laboratory on rammed earth. As I walked around David’s lab, he explained to me how he has built this state of the art lab with the aid of National Science Foundation (NSF). I was encouraged to see that the United States’ government is supportive of the sustainable building technology. David had built a truly magnificent laboratory equipped with all sorts of machinery to measure everything that could potentially be measured on his new technological marvel, the Watershed Block. In the front portion of his lab, he was conducting tests on strength, drop testing, water absorption, contraction, expansion and many other tests which we did not have time to delve into.

His lab was well equipped beyond any other lab I had seen. He explained his vision of how he thought the Watershed Block could be built with little or no cement, yet capable of meeting the needs of our modern day construction practices. His Watershed Block resembled an ordinary concrete block, but the cement content is substantially reduced. I was amazed at the strength of David’s Watershed Block. The natural question was how was he able to get such amazing strength? Then David explained how he had to invent a kind of rammed earth pressing machine, capable of putting tremendous amount of force on these blocks and this force was key to creating the strength needed. As we walked together to the back of his lab, he showed me his machine connected to conveyor belts and motors powering it. This second generation machine was capable of producing 4 blocks every minute. Connected to the machine were long conveyor belts carrying the blocks away from the pressing machine. It was easy to get impressed by all the technology in David’s laboratory.

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Rammed earth home in Northern California built by Easton's Rammed Earth Works

After visiting David’s lab, it was time to visit some of the houses built using David’s technology. David drove me to visit some modern rammed earth homes and their owners. They graciously welcomed us into their homes and shared their stories, opinions and passion of rammed earth with me. They told me the reasons they chose and love their rammed earth homes. Thanks to all the modern rammed earth home owners for their encouraging words. Their stories, their opinions, their love of rammed earth will contribute to the rammed earth construction development in China.

On the evening of August 22, 2015, an event was hosted by Mr. Hamel in the beautiful Hamel Family Winery to showcase rammed earth construction. I was the invited speaker. I was impressed by the amazingly beautiful new winery which was built with massive rammed earth walls perfectly becoming a part of natural landscape. It is an obvious masterpiece of modern architecture. I am not a wine expert, but I was told the wine was excellent. Wonderful hospitality, great wines, beautiful view from inside and outside, what an unforgettable experience! The Hamel family were such gracious hosts. They had paid attention to every detail. I will always remember their hospitality. Many thanks to the Hamel family!

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Dr. Rongrong Hu at the Hamel Family Winery before her presentation on the history and future of rammed earth in China.

There were guests from every walk of life. Some were architects and engineers, some had their homes built with rammed earth, yet others were just intrigued with the technology and were considering construction projects. I had prepared a presentation on rammed earth history in China and how we have started to use this technology again to solve our modern day pollution problems.

My presentation was full of colorful pictures on China’s popular rammed earth monuments. It probably went longer than I expected. After the presentation, I expected most guests to dash out of auditorium given I went over my allotted time.

However to my surprise, many of the audience came to the podium after the presentation to ask about rammed earth construction today in China. They were all hopeful that rammed earth becomes mainstream in Chinese construction, especially in rural China. The guests also shared their stories and opinions on rammed earth construction. They all believed rammed earth construction has a bright future because of its history, light carbon footprint, beauty, and comfort.

After the event I wanted to do a more thorough survey. I was wondering how the guests really felt about rammed earth. The responses were overwhelmingly positive on rammed earth. I took the liberty of compiling some of the guest responses at the end of this note.

I had a great time in the beautiful Napa Valley. And I owe gratitude to many. Specially, I like to thank David any Cindy Easton for inviting me to Napa and hosting me at their beautiful home. Their inviting hospitality made me feel right at home. I also like to thank the Hamel family again for the wonderful event they hosted. I am grateful for all their hospitality.

Last but not least, I like to thank all the guests came to the event who shared their valuable opinions with me and thank the home owners who welcomed me to their homes. Their valuable opinions will guide me and others in the Chinese academia in shaping the future of rammed earth construction.

“I truly believe rammed earth construction has a future, especially as we try to change our construction methods/techniques to protect the planet and ensure a healthier environment for future generations.”

“I think that’s the key to the future of rammed earth - it’s past. History has proven it’s beauty, functionality, and resiliency.”

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Dr. Rongrong Hu speaking about the history and future of rammed earth in China to a group of rammed earth advocates knowledgeable about rammed earth in the United States.

“Rammed earth is usually reserved for those US projects with a healthy budget. It will be interesting to see if the Chinese can do it affordably and safely. I am even more excited about the future of your rammed earth CMU as it is a valuable tool for Architects. Since the price is similar to concrete CMU, the real advantage is that you achieve an extremely attractive interior and exterior finish, that’s the REAL savings.”

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Dr. Rongrong Hu speaking with attendees of her presentation asking them their feelings on the future of rammed earth.

“The answer is ‘absolutely yes, rammed earth has a big future.’ In a century where population growth and rising standard of living demands more and better housing - at the same time as our most precious resources of clean air and pure water are diminished - it is imperative and inevitable that we find ways to build that have a lighter carbon footprint, and less impact in general on resources. The efficiency of rammed earth, from the perspective of its very small carbon output, its ease of manufacture, and assembly, and its reduction in operating costs for the resident, all make it a certain winner in the race for better building techniques. In the words of a great Hollywood film, Back to the Future!!”

“Do I think rammed earth has a future? Absolutely, having enjoyed lived in a rammed earth home for 15 years it is hard for me to imagine not living with the beauty, sustainability, convenience and comfort of living in this earth home.

What I enjoy most about rammed earth is the beauty and solid structure. I also feel a sense of stability and strength from the home, having experienced a 6.0 earthquake close to the epicenter without an item out of place. Education for architects, building contractors, and building departments to familiarize with the design and engineering techniques and developing a cost structure to compete with traditional building methods will hopefully change this in the future.

The work that David Easton and his colleagues in the industry are spearheading, including the availability of techniques like the rammed earth blocks, may be key to the future of rammed earth. I certainly hope that this method will bring the wonderful lifestyle of this building to many around the world.”

Windhover Contemplative Center wins Best of Competition in the 2015 International Interior Design Association's interior design competition.

We're thrilled to hear the news that the rammed earth Windhover Contemplative Center was just awarded the Best of Competition in the 2015 International Interior Design Association's Interior Design Competition. The award was given at the annual Award Gala in Chicago.

In addition to the Honor Award, the rammed earth project was bestowed the Best of Competition award, top among over 450 entrees from around the world.

The rammed earth Windhover Contemplative Center featured on the front and back cover of the awards catalog for the 2015 International Interior Design Association's Interior Design Competition.

Windhover Contemplative Center award page detailing the Best of Competition award.

Own a beautiful rammed earth vacation property in Hana, Hawaii.

One of Rammed Earth Works' jewel properties, the vacation home in Hana, Hawaii, is currently for sale. 

Interestingly, on the other side of the island, another rammed earth property is for sale - the $20 million "surf hut" owned by the world's most financially successful photographer - Peter Lik - and designed by Tom Kundig.

David Easton Keynotes the First International Conference on Rammed Earth Construction - Perth, Australia - February 10th to 13th 2015

David Easton is thrilled to keynote the First International Conference on Rammed Earth Construction in Perth, Australia from 10 to 13 February 2015. The conference is hosted hosted by The University of Western Australia and will bring together researchers, engineers and practitioners in order to communicate the latest developments in the design and analysis of rammed earth structures.

David's keynote will focus on themes of creating unified definitions and standards for rammed earth construction as well as increasing the sustainability profile of rammed earth by limiting or eliminating Portland cement from mix designs.

Here are a few select quotes from the keynote :

“Who in his right mind would believe that you could simply pound dirt into durable shelter - that walls built this way could stand up to wind, weather, and gravity? Who in his right mind would think you could make a business out of such a thing, that people would actually pay for it? What were we thinking? That here was an opportunity to support our families and put our kids through college? That we would get rich and successful and launch a global renaissance? Mark Twain once said, ‘it takes two things to be successful in life - ignorance and confidence.’ Look at us old timers today. What in the world made us stick with the idea of rammed earth? Was it ignorance, or confidence?”

“Is rammed earth only pure compacted soil or is it any aggregate pounded into a monolithic wall, whether or not blended with stabilizer? Is it the act of ramming, or the composition of the earth? Is a poured earth wall rammed earth? Is a shot earth wall rammed earth? Is a wall of compressed earth blocks rammed earth? What defines rammed earth? The material, the method, or it’s monolithic character? Does cement stabilization change the character of the wall so much that we can no longer call it rammed earth?”

“Why do the world’s codes differ so radically on the perception of what is safe rammed earth - 0.25 MPa (30psi) in some countries, 17 MPa in others? In soils, it takes a minimum of 10% Portland cement to achieve strengths of 17 MPa, less cement in crushed aggregate. What this means, distressingly, is that there is nearly twice the cement in a 400 mm stabilized earth wall than there is in a typical concrete wall, and every pound of cement calcined generates nearly a pound of CO2.”

“What is it that makes rammed earth so attractive, so alluring, so captivating? What exactly is the magic? Is it simply the hygroscopic ability of raw earth to maintain optimum humidity levels within a space? Or is it the way thick earth walls can soften sounds and provoke a sense of calm? Perhaps they capture the essence of biophilic design, that the earth walls provide a source and sense of connection to the natural world, distilling natural materials to their elegant simplicity and rightness of fit.”

“The recent interest in biophilia - architecture to connect people with nature - could not find a better mascot, a better poster child than rammed earth. A thick, strong earth wall acts like a filter, excluding the noise and the stress that is outside, creating a positive, beneficial environment within. It’s pure and simple.”

Read the full keynote here.

Artist Andy Goldsworthy Uses Rammed Earth Works for Newest Art Installation

Rammed Earth Works is thrilled to have worked with renowned artist Andy Goldsworthy on his most recent installation in the Presidio, called Earth Wall. The piece is Andy's fourth for the For Site Foundation, following “Spire” (2008), “Wood Line” (2011), and “Tree Fall” (2013).

“We’re looking at a wall made from earth from the Presidio and embedded in the wall is a ball of branches and earth that appears to have been excavated out of the wall,” Andy says. “The branches have the appearance of having been there for an awful long time, and that was a very strange thing because you’re always trying to see your work outside yourself, and it looks like I dug something up from a long time ago that I hadn’t even put there, so it was a real process of discovery for me, as I hope it will be for other people.”

Andy digs out a ball of gnarled eucalyptus branches embedded inside a rammed earth wall.

Andy selected rammed earth as the medium around the twisted branches to give the appearance of the eucalyptus having been buried under layers of earth deposited and compacted over a long period of time. The rammed earth “simulated layers of earth laid down over time, as if the layers were made as sedimentary layers. We did in a day what nature would have deposited and compacted over thousands of years” says Khyber Easton of Rammed Earth Works.

“Prior to this Andy Goldsworthy project, Rammed Earth Works had always been building structural walls. Now artists are asking to build aesthetic, conceptual projects. This Goldsworthy project highlights conceptual aspects of rammed earth and legitimizes rammed earth as a medium of art, not just structure.”

Rammed Earth Works is thrilled to have worked with Andy on such a timeless piece. Below is a short video via The Presidio of San Francisco followed by a series of production images detailing the installation of Andy Goldsworthy's Earth Wall at The Presidio.

Eucalyptus branches from the Presidio installed before the formwork for the rammed earth wall is installed.

Formwork for the rammed earth walls installed, locally sourced Presidio earth mixed and poured into the forms, and ramming begins. Rammers carefully compact earth around the twisted ball of  Eucalyptus branches.

Some passion filled earth ramming.

Rammers have reached the top of the rammed earth wall that surrounds the now buried eucalyptus branches.

Formwork is removed revealing a freshly packed rammed earth wall and the center point of the ball of gnarled eucalyptus branches. Both the raw earth for the rammed earth wall and the eucalyptus wood was sourced from the surrounding Presidio.

Artist Andy Goldsworthy poses with the installation before beginning to dig out the earth surrounding the encased eucalyptus wood.

Detail of the rammed earth wall.

Artist Andy Goldsworthy poses with the installation before beginning to dig out the earth surrounding the encased eucalyptus wood.

Detail of the rammed earth wall.

Artist Andy Goldsworthy excavates the rammed earth from around the gnarled eucalyptus wood.

Detail of the buried then revealed eucalyptus branches surrounded by a rammed earth wall.

Rammed Earth Works' Khyber Easton and artist Andy Goldsworthy.

Artist's quotes sourced from this SF Gate article.

Our New Website is Up!

After months of work, we've got a new website up promoting our 30 years as the original rammed earth builders in the U.S.

Thanks to David Easton, Dan Alvarado and Alex Wright for the production of the new website!

Indoor Comfort Isn’t Just About R-value: Addressing the Relationship Between Insulation and Thermal Mass

This post was originally published by our sister company Watershed Materials

People often ask us about the R-value of a Watershed Block, or of a wall built of Watershed Block, or of a rammed earth wall built by our sister company Rammed Earth Works. For many good reasons, the building industry is highly interested in insulation. Reducing heating and cooling costs is paramount in reducing the overall embodied energy of our built environment. However, focusing on insulation alone (R-value) as a mechanism to ensure indoor comfort with lowered heating and cooling costs overlooks another key element of the equation - thermal mass.

The relationship between insulation and thermal mass is nuanced. Insulation reduces the movement of heat, while thermal mass has the effect of storing heat. Insulation, while very good at slowing the movement of heat, generally has little to no capacity to store heat. By contrast, thermal mass, while very good at storing heat, generally has a relatively poor ability to slow the movement of heat. Despite these differences, the comfort of indoor environments can be efficiently maintained by employing either insulation or thermal mass, or a combination of both.

The thick earth walls of China Fujian Tulou, here shown in the Hekeng cluster, have been providing their inhabitants with cool daytime temperatures and warm nighttime temperatures for hundreds of years. Image credit Fon Zhou, used with permission of Creative Commons Attribution-NonCommercial 2.0 license. 

These two mechanisms inform two distinctive strategies for maintaining stable indoor temperature and comfort. The first strategy uses thorough insulation and vapor barriers to effectively separate indoor air from outdoor air. A complex heating and air-conditioning system then circulates indoor air. Efficiency is gained through using as little heating and cooling as possible, with the HVAC unit often drawing on the exhaust air to pre-heat (or pre-cool) intake air in a sort of temperature exchange. The second strategy instead relies on a concept of a thermal flywheel to naturally heat or cool thick masonry or earthen walls that store this temperature and naturally regulate indoor air temperature, often with little to no heating or cooling.

Exterior walls of homes that embrace modern construction concepts including Passive House and Net Zero often seal off exterior air from interior air with impermeable vapor barriers and high amounts of insulation. Heat exchanging ventilation systems circulate air. Image credit NBT used with permission of Creative Commons Attribution No Derivitives 2.0 license.

Each strategy has its merits and downsides. The first strategy relies on complex heating and cooling systems that may not function during power outages or after mechanical failures. Additionally, a fully insulated and vapor sealed building does not “breathe” naturally, raising concerns of air quality. The indoor air quality of sealed buildings is such an issue the California Building Code now requires additional mechanical ventilation to bring in fresh air in all new construction.

The second strategy, while relying less on complex heating and cooling systems, relies instead on fluctuations between the nighttime and daytime temperatures, known as diurnal swing. Without these temperature fluctuations, the thermal flywheel mechanism doesn’t function and little energy savings are achieved.

With the above as background to the discussion, how do we answer the question when asked to put a number on the R-value of a Watershed Block or a Watershed Block wall, or a rammed earth wall? A Watershed Block, like rammed earth, has a relatively low R-value. That’s the point, after all, of materials with a high thermal mass. A Watershed Block, like a rammed earth wall, has to move heat in order to store heat. Even with a low R-value, a Watershed Block wall, like any earthen wall, can still contribute to maintaining a comfortable indoor air temperature. And, a low R-value does not mean that a Watershed Block or rammed earth wall needs to be insulated.

Let’s examine the two questions separately - how can a Watershed Block wall, like a rammed earth wall, provide insulative properties while having a low R-value, and, what is the effect of adding insulation to a Watershed Block wall or a rammed earth wall?

The first question - how can a Watershed Block wall, or  a rammed earth wall, provide insulative properties while having a low R-value -  examines the idea of “effective R-value”, otherwise (and more accurately) known as “mass enhanced R-value.” The difference between R-value and “effective R-value” / “mass enhanced R-value” can be understood by examining the difference between the lab environments in which R-value is measured versus the real world environments in which building materials are used.

R-value is measured technically in a lab, specifically in a machine called a guarded hot box. One side of a material - whether fiberglass, a Watershed Block, or a sheet of drywall - is maintained at a constant temperature. The other side of the material is kept at a different constant temperature. The amount of energy required to maintain this temperature difference is measured, and an R-value is determined.

This specific R-value is a “steady-state” R-value and reflects the material’s ability (or lack thereof) to insulate against two constantly different temperatures. What about the real world in which temperature differences are dynamic, not steady?

In much of the United States, the outside air temperature changes greatly over a 24 hour period, a situation referred to as diurnal swing. In the desert environments and Mediterranean climates that dominate the West and Southwest, the temperature outdoors changes greatly during the day, rising above a comfortable indoor temperature in the afternoon then falling far below a comfortable indoor temperature at night. Over a course of 8-12 hours, the temperatures on two sides of an exterior wall can change dramatically. So the steady state R-value determined in a lab is no longer so valuable in determining how the indoor temperature can be best maintained when applied to a dynamically changing outdoor temperature.

From this more dynamic and changing environment, the concept of “effective R-value” / “mass enhanced R-value” has emerged and relates to the idea of high mass exterior walls functioning as a thermal flywheel. Warm daytime temperatures and direct sun slowly warm exterior walls but this heat does not reach interior spaces until after the sun has set. The latent daytime heat in the exterior walls warms interior spaces during the evening, at which point the process reverses and the walls slowly begin to expel the daytime heat through the thick exterior walls into the now cooler nighttime air. By morning, the thick exterior walls have cooled again, and the process continues, offsetting the daytime heat to the evening and the evening cool to the daytime.

The thick exterior walls of a rammed earth house can provide insulative properties above the measured steady state R-value when used in climates where the daytime and nighttime temperatures swing above and below the desired indoor air temperature, also known as high diurnal swing.

In this way, thick earthen exterior walls can have a higher “effective R-value” that is determined by via computer modeling to determine what a similar steady state wall R-value would need to be to offer the same performance.

However, key to the concept of “effective R-value” / “mass enhanced R-value” is where and how the material is used. A thick exterior earthen wall will have a higher effective R-value, but only in certain climates where the diurnal temperature swing allows for this thermal flywheel performance. That same wall in a consistently cold climate - one where the exterior temperature is always below a comfortable indoor temperature - will have no effective R-value improvement. So the answer to the first question - how can a Watershed Block wall, like a rammed earth wall, provide insulative properties while having a low R-value -  has to do with the environment where the wall is used. In an environment where the diurnal temperature swing allows for a thermal flywheel performance, a thick earthen wall can provide insulative properties, and a higher effective R-value despite having a low measured steady state R-value. However, in an environment without a diurnal temperature swing, a thick earthen wall does not provide significant insulative properties beyond its measured steady state R-value.

The second question - what is the effect of adding insulation to a Watershed Block wall or a rammed earth wall - follows much of the above discussion and examines how thick earth walls, either exterior or interior, can be used effectively in climates in which the temperature is consistently above or below a desired indoor temperature. Additionally, new building regulations like California’s Title 24 virtually mandate insulation, regardless of a wall system's thermal storage capacity. So what is the effect of insulating thick exterior earth walls? Again, location and local climate conditions are key to the answer.

In an ongoing study to determine the most effective use of structure and energy performance, this wall assembly of double block provides one set of hollow cells to receive reinforcing steel and concrete grout to support roof loads and provide earthquake safety, with one set of cells left open to capture dead air space to improve thermal resistance. This wall assembly will have a different thermal response depending on which side of the house it's located. The north side will tend to be much cooler than the south and west because it never sees direct sunlight.

In a Mediterranean / desert climate like the American West and Southwest with relatively high diurnal temperature swings, adding insulation to thick exterior earthen walls halts the functionality of the thermal flywheel described above. Warm daytime temperatures cannot reach indoor spaces to warm the interior space at night. And the cool night air cannot expel the home’s heat in the pre-sunrise night. Insulation added to exterior walls will do exactly what insulation does best - stop heat transfer.

In climates with long periods of consistent cold or consistent heat, insulation is necessary even in thick exterior earthen walls. However, the mass-effect of using materials with high thermal storage capacity can still provide noticeable benefits to indoor air comfort. High mass earthen walls used inside the insulation envelope will slow indoor temperature swings and regulate indoor humidity. Used outside the insulation envelope, high mass earthen walls can delay intense heating from direct sun by shifting the time that heat reaches the insulation envelope to the evening when cooling systems are more efficient.

The effect of adding insulation to a Watershed Block wall or a rammed earth wall is highly debated, especially in environments most appropriate to thermal flywheel heating and cooling. Recent energy code changes in California further amplify the debate. The role of high thermal mass wall structures has not been consistently integrated into concepts of highly insulated net-zero construction.

So to answer a question with another question, how are you incorporating insulation with thermal mass, and in what climate?

Further reading :

http://www2.buildinggreen.com/article/thermal-mass-what-it-and-when-it-improves-comfort

http://www2.buildinggreen.com/article/thermal-mass-and-r-value-making-sense-confusing-issue (requires a paid account to BuildingGreen.com / Environmental Building News)

http://www.passivebuildings.ca/resources/Documents/RammedEarthForAColdClimate-StuFix.pdf

http://ceramics.org/wp-content/uploads/2013/05/sanders.pdf

http://www.crockerltd.net/adobe_thermalmass.htm

Building From The Watershed

One of the primal attractions to building with earth is harvesting raw materials from the construction site itself. In the old days (pre-industrial revolution), that was always the case. Soil dug from the foundation trenches or from a nearby borrow pit was either molded into sun dried bricks and laid up into block walls or rammed between wooden form boards into monolithic walls. Man converting raw local resources into shelter is truly sustainable building.

During the past decade or two, the earthbuilding industry has drifted away from this core precept, settling into the comfort zone that comes from using familiar and consistent quarry-processed aggregates. This quest for comfort has come at an environmental cost.

Don’t get me wrong, I am all in favor of consistency and dependable results, but I’ve also become more aware of the carbon consequence of putting trucks on the road, burning diesel fuel, wearing out rubber, and pounding asphalt. I trucked quarry materials to our rammed earth and pise jobsites for years, but I now believe the right path is to improve our understanding of local geology and our skills at formulating mix designs to allow us to incorporate even more of each site’s unique resources.

I think of it as the construction industry’s version of the slow food and locavore movements - better quality, closer to home. I want to call it “building from the watershed”. The goal is to develop a series of protocols that allow us to evaluate any found soil and predict how it will perform in a structural capacity. When we complete the assembly of this soils library, we will then have the ability to reproduce consistent results from site to site, using fewer quarry amendments and thereby reducing the number of trucks on the road and CO2 in the atmosphere. Carbon offset construction.

A Modern Rammed Earth Home in Silicon Valley

David Easton has directed the construction of hundreds of homes around the country and the world, but began taking on a special job over the past few years - building homes for his children. With decades of experience, David had the perfect opportunity to apply the best of his techniques, including stacking modular formwork, to help his step-son, Jack, construct a modern rammed earth home Silicon Valley.

The entire construction process has been thoroughly documented here. And below find a series of highlight images from the build.

Keeping the Costs Down

One of the challenges facing the popularization of rammed earth is it’s installed cost.  It’s ironic that what might be viewed as a free raw material has evolved into an expensive finished product. In the past, probably the greatest appeal to building with rammed earth was its low cost. 

Soil was harvested on site, the forms were simple, and the work was done by hand.  Buildings served basic needs, with walls that were rough and only more or less plumb.  This practice remained the norm for a very long time, from early civilization through the middle of the twentieth century.  It still is the norm in rural China, the Middle East, and Africa.

When rammed earth began to re-emerge in the mid 1970’s, it was still considered an inexpensive wall system.  Soil was predominantly sourced on site, formwork was relatively simple, the architecture was linear, and unskilled labor could be used for most of the work.  Walls were a little ragged and unrefined.  Plaster was a common finish treatment.

Over the past few decades, rammed earth has grown in popularity, with an increasing number of professional builders developing the requisite skills.  Contrary to the law of supply and demand, however, in which competition reduces prices, rammed earth has become more expensive. 

Why is this?  The answer is complex, or rather complexity.  Rammed earth began as a simple system that recognized, even celebrated, the inherent flaws and unpredictability of raw earth. Over time, as builders improved their skills and the marketplace grew to appreciate the unique beauty of rammed earth, architects began to push the material to applications and expectations that were extremely difficult to fulfill. They were difficult but not impossible, only time consuming and expensive.  Gone were the days of simple forms, unskilled labor, and site-sourced materials.  In their place were elaborate formwork built and set by highly skilled carpenters, and imported screened soil and processed aggregates stabilized with 10% cement. Each course of soil in the forms must be carefully placed and conscientiously compacted, with the whole installation under the watchful eye of a paid special inspector.  Add color blending, strata lines, curves, rakes, niches, lintels, chamfered bond beams and watch the square foot cost approach Carrara marble. 

What can we do?  There are two solutions, and the good news is that they can co-exist.  On one hand we can continue to refine our skills and produce rammed earth with the look, feel, and price tag of art.  On the other hand, we can provide clients and architects with value engineering feedback on how to design efficiently for the material.

Rammed Earth is massive so keep it simple.  Rammed Earth is regional so source materials locally.  Appreciating the unpredictable character of finished wall surface celebrates the authenticity of natural materials and showcases its hand built qualities.

Rammed earth doesn’t have to be expensive.  Designed with the system in mind, it can be one of the best values in the building industry today.

A Contemporary Rammed Earth Home in the Mountains

David Easton has directed the construction of hundreds of homes around the country and the world, but began taking on a special job over the past few years - building homes for his children. With decades of experience, David had the perfect opportunity to apply the best of his techniques, including economic re-use of formwork and site sourced resources to help his daughter, Terra, construct a modern rammed earth home high in the California mountains.

The entire construction process has been thoroughly documented here. And below find a series of highlight images from the build.

Why Not Concrete

Although I’ve been asked this question a hundred times, by engineers, building officials, concrete contractors, and other skeptics, I’m always a bit unprepared for it.

I first started building with rammed earth nearly forty years ago in a quest for low-cost construction solutions and with a certainty that sourcing “free” material from the site had to be economical.  Over the years, as code compliance and client preference compelled us to achieve higher strengths and more uniform wall quality, we found ourselves forced to import quarry products and stabilize with higher cement ratios.  In effect we were pulled by market forces towards a product that was indeed akin to concrete.

Hence my difficulty with the question.  Is rammed earth less expensive than concrete?  Does it represent a reduction in carbon footprint?  Is it stronger or more durable?  Is it less expensive to heat and cool?  Does it improve indoor air quality?  Is it healthier?  Is it more attractive?  Is it better for the planet?

First, rammed earth is not necessarily less expensive than concrete.  Even though the forming systems for the two materials are similar and take more or less the same man-hours to erect, layering and compacting rammed earth into the form takes considerably more labor and equipment than pouring and vibrating concrete.  The only savings possible are a reduction in aggregate and cement costs.  To achieve these savings a mix design must be developed that utilizes a major portion of either on-site or other free mineral soil and a minimum rate of stabilization. 

Rammed earth can represent a much lower carbon footprint than concrete.  If the soil for the walls is close to the project, then transportation fuel consumption will be low.  If careful formulation allows design strengths to be met with 7% or less cement, then a big savings in CO2 will accrue.  The question of design strength is another challenge altogether.  Where some structural engineers are comfortable designing one and two-story rammed earth walls with an f’c of 600 psi, other engineers specify strengths as high as 1500 psi.  A design strength of 600 psi can be attained in an ideal soil blend with 1-1/2 sacks of cement per yard, but it can take up to 3-1/2 sacks to get 1500 psi.  What this shows is that engineering design plays a big role in carbon reduction.

Is rammed earth stronger or more durable than concrete?  The answer is clearly no, but the question should be: is rammed earth strong and durable enough for its intended purpose?  If the soil is selected correctly and the wall built properly, then rammed earth meets all the required performance standards and will provide decades of serviceability with little or no maintenance.  Rammed earth has an inherent beauty that transmits a warmth and natural character very different from concrete. 

Rammed earth walls are typically much thicker than a concrete wall, which makes them much more effective at controlling indoor temperature fluctuations.  An 18” wide wall creates a 12-hour thermal flywheel - outside temperatures take half a day to migrate through the wall to the inside face.  This means a mass wall balances out diurnal temperature swings.  In most climates and with proper exterior shading, this makes for no cooling loads.  Heating loads vary considerably based on orientation and building design.  Heating and cooling efficiency are big contributors to energy consumption and carbon footprint reduction. 

Finally, the questions about whether rammed earth is healthier for the occupants or for the planet.  Many people, especially in Europe, believe that clay in an interior wall works to maintain optimum indoor humidity, which in turn results in improved indoor air quality.  Certainly, natural earth walls are more healthy than materials that may be off-gassing glues, paints, resins, or other chemicals.  There are no factories exposing workers to toxins.  Rammed earth walls create quiet spaces that resonate solidness, which can be perceived of as an increased sense of comfort and well-being.  As for the impact on the planet, rammed earth uses fewer resources, both in construction and over the life-span of the house. 

Finding the Right Soil

Clay/sand ratio has the greatest contributing effect on how well an earth wall will perform.  Traditionally, for raw rammed earth, that ratio has been established as 30% clay and 70% sand. 

When using cement as a stabilizer, clay content can be reduced, in some cases and with high stabilization rates, clay (and other fines) can be as low as 8% to 10%, depending on numerous factors (uniformity of gradation, plasticity, particle shape, and parent rock).
Unlike earlier times, when the building material was nearly always harvested on or near the construction site, today we have access to a wide range of importable mineral soils and admixtures.  Formulating a blend of soils capable of achieving optimum structural performance is our objective.

To do this, we begin by looking at the underlying soil on the building site itself.  A review of the boring logs from the geotechnical report will yield valuable data:  gradation, USCS soil type, and in some cases a plasticity index.  We have found that most site soils can be used in some proportion to create a useable formulation.  Using site soil has several advantages:  reduced cost of importing materials, increased LEEDs points, color continuity with the local geology, reduced off-haul costs, and reduced carbon emissions from construction.

The gradation report (also called a sieve analysis) identifies how much of a given soil is fine particles, those passing the 200 mesh screen.  The Plasticity Index is an indicator of how much of those fine particles are “clayey”.  Clay particles help to bind together the soil matrix.  If the gradation indicates more than 25% passing 200, the addition of sand will likely be required.  High clay soils also benefit from small gravel as supplemental amendments.  

If boring logs and site investigation indicate utter unsuitability, or if there is no excavation planned for the site, it is possible to source a portion of the wall building material in other ways.  Excavating contractors, pool contractors, or other general contractors frequently have excess material they need to move off site.  Phone calls or scouting trips can be productive, as is the old “Clean Fill Wanted” sign.  

For the required amendments to site or other free material, you can start the search for a suitable sand or gravel amendment at the local masonry or landscape supply yards.  Coarse sands with a good distribution of particle sizes are usually better than fine or uniform sand.  Cracked or crushed gravel is better than “pea” or river gravel because of its angularity.  Color and cost are also important considerations. 

For a small project and for all of the required pre-construction testing, the search can end at the supply yard.  For larger projects where several truck loads of amendment will be required, you will be able to negotiate a better price dealing directly with the quarry.  

Finally, if site soil is unsuitable and free clean fill is unavailable, or if screening and processing is impractical, then purchasing and importing all of the wall building material from a quarry is the logical choice.  Cost, travel distance, color, wall density, required stabilization and geo-regionalism will dictate which quarry to use.