The Cob Mix

"Cob" as a natural building material is a term that most find unfamiliar outside the sustainable building community.  Cob is essentially a mix of straw and clay soil. When I use the word 'cob' in this blog I normally provide a link to wikipedia so the reader can get a good definition. Click here to learn more.
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In this entry I'm going to focus on how I make cob and some background on cob as a building material.

I use an 8-horsepower concrete mixer with a 1-cubic yard capacity, instead of hand-mixing.  My walls are up to 2-feet thick and I estimate that when completed, I will have applied between 40-50 tons of cob to make the walls of my studio.  In order to finish the building in my lifetime, I find the mixer an essential tool to make the 2,000 pounds of cob I can apply to the walls on a productive day of 'cobbing'.

When using a mixer, the batch of cob needs to be wetter than if mixed by hand.  This is because if the straw-clay is too dry it will 'ball-up' in the rotating drum and not mix throughly.  I usually start with about 15-20 gallons of water, then start the mixer.  I throw in about a 14-inch section of straw from a 3-strand straw bale. As the mixer rotates, the straw thouroghly mixes with the water.  At that point I begin to shovel in the clay soil.  The clay is first sifted through a 1/2" screen to remove rocks and other inclusions.

Note that my soil is almost pure clay and some books recommend adding sand to the mix.  This helps keep the clay from developing cracks when drying.  I decided that I didn't want to have to haul in sand for this project, so what I did to compensate for the lack of sand was add more straw to the mix.  I'm finding that this works fine with very little cracking in my walls to date.

I continue to shovel in clay soil into the mixer until the batch looks like this composition (consistency) as shown in the above photo.

I call 'cob' natures fiberglass.  The interlocking fibers of straw in a clay emulsion are similiar to glass fibers in an epoxy polymer (fiberglass).  Two feet thick of cob provides a high-strength monolithic wall, that is both a structural (weight supporting) and a thermal mass system to mitigate large swings in outside air temperature, thus keeping a structure comfortable and/or requiring very little heating in the winter and cooling in the summer.

A Dry, Hot Summer

The upside of a disappointing summer monsoon season was suppose to be more time spent applying cob to the walls of the studio and less time dealing with muddy ground and erosion. However; record heat, vacation travel and other work reduced the amount of hours dedicated to the studio. Now that September has arrived, the tail end of the real hot weather has only about 3-4 weeks remaining. I'm looking forward to the cooler weather.
Photo: Peggy Santello

Mesquite Wood Lintels

With a wall thickness of the studio up to 2-feet in width, I wanted to utilize another local resource, 'Mesquite', to span and support loads above each window opening. Prior to the addition of the Mesquite wood, the previous blog (see the July 15 entry) documented the first step of casting a concrete lintel above the rough window frame. Visible in the photo below, the face of the concrete lintel will eventually be finished with an artistic ceramic tile design.

CLICK ON ANY PHOTO TO ENLARGE

The first step was to cut 36-inch lengths of mesquite from trees on my property. Mesquite is prevalent in the Arivaca area and selectively cutting branches from various trees ensures the sustainability of this renewable resource.

The next step is to strip the bark off the logs using a 'draw-knife' (shown in the photo at right). The photo shows the progression until the log is stripped bare of bark, sanded and coated with Tung Oil.

The close up photo (left) shows the beauty of mesquite and the richness of the wood grain brought-out by application of the Tung Oil.

Mesquite wood is extremely dense, strong and durable; thus ideal for this structural application. In addition, its striking beauty and a local (southwestern) resource makes it ideal in any natural building aesthetic.

The process is a lot of hard labor. It took two days to cut, prepare and 'cob' in the wall these four mesquite lintels.

Other uses for Mesquite include harvesting pods as a food resource and exquisite furniture made right here in Arivaca.

Cast-In-Place Lintel

A 'Lintel' is a beam that spans an unsupported space (like a door, passage-way, or, window in this case). The purpose for the lintel is to prevent compromising of the wall, as forces resulting from the weight of the adobe wall above the window frame, press downwards on the fragile frame and window.

Traditionally, adobe homes used wood lintels. However, today the building codes in your area may not allow wood lintels, specifying a concrete or steel beam instead. The code has concern that wood lintels may decay over time due to weather or bug infestation.

As a result, my solution is to provide for both strength and aesthetic by casting in place a concrete beam and later bolting a mesquite wood face plate. See photo example of the finished wood facing and trim in an adobe out-building I constructed a few years back (below).

In the picture above, you can see I scuplted the 'cob' walls on each side of the window so they can be filled with concete and span the window opening. I used two pieces of vertical rebar that were placed when the stone stem wall was being constructed, to secure a horizontal piece of rebar as reinforcent of the lintel. The lintel is 4"-high and 5"-wide and spans the cob wall about 12" in each side of the window. Note that I made cob walls at the base (of the form), about 3/4" higher than the top of the window frame. That way, the poured concrete in the form will not be directly resting on the window frame, thus defeating the purpose of the support in the first place. To account for the 3/4" gap above the wood frame, I cut a strip of insulating foam board (see photo above and below). The concrete will rest on the foam instead.

In the photo to left, observe one of the two anchor bolts I added. The threadede end extends through the wood form. These bolts will 'anchor' the mesquite wood face plate that will be added later as a finishing touch along with the trim.

The photo below shows the poured concrete lintel with the wood form removed. Notice the two anchor bolts and foam between the lintel and the wood window frame. The rocks embedded in the concrete on top of the lintel will give the 'cob' that will be placed on top of the lintel something to grab onto.

You may have noticed that the width of the lintel does not cover the approximate 2-foot width of the massive cob wall; only the width of the window frame. I need to address this and will present a solution in a future blog entry.

Photo at right show an example of the mesquite wood face-plate and trim on another finished adobe I completed (click on photo to enlarge for a better view).

Progress Photo

CLICK ON IMAGE TO ENLARGE

West Wall Reaching Ceiling Height

A portion of the west wall has reached ceiling height (9ft). Remember that from this view, the wall is partially 'bermed'; therefore, on the inside at floor level this room is essentially below ground.

If you look carefully you can see a string along the top - set with a line level - that's the final height I'm working toward.

Also in the photo at right, there is a 'form' set up to eventually pour a concrete 'lintel' above the window. More on that in a future post.

Adobe Brick Wall

As part of the architectual look of the studio, I wanted to create the effect of a newer earthen building built on top of an old adobe 'ruin'. Therefore I'm constructing two partial adobe brick walls on each side of a doorway in the studio

I had about 110 of these adobe bricks left over from another project and decided to integrate them into the building design. The adobe bricks are made with 40% clay and 60% sand (unstabilized). You may be able to tell from the picture (click on photo to enlarge), that I applied a clay coating over the bricks to help protect them from the expected summer rains.

You can see this wall in context to the whole structure in other posts to this blog.

Honeycomb Calcite Lighting Effect

The photo below shows a portion of the bermed west wall above ground level. The wall height at this section of the building is nearing completion. The glass block window allows afternoon light to enter a 'mirrored' rectangular chamber in the 2-foot thick wall before stiking a translucent Honeycomb Calcite stone positioned on the inside wall (see other photos below).The photo to the left shows the Honeycomb Calcite stone in the interior of the 10-foot diameter "Kiva" room of the studio.

A close-up photo (right) reveals the beautiful orange-yellow color of the stone. Once the room is completed, light entering from the western sky will illuminate the stone to produce a striking glow in the room.

Cob Progress Photos

Despite 95-deg F temperatures here in Arizona, 'cobbing' continues at a relentless pace. I'm able to set and sculpt about 5-wheel barrows of cob a day. Each wheel barrow load is about 200-lbs, so that's about 1/2 ton. Therefore, 20-days work so far is about 10-ton of cob in the walls.

As you can see from the above photo, the walls are massive; 2-feet thick or more. Since I'm not using any sand in my cob mix, I'm adding extra straw to prevent cracks from forming. So far no problems. The lone wall with adobe block (see earlier blog) is looking cool!

Styling with Adobe Block

The doorway show on the left will have adobe blocks that, when finished, will stair-step down away from the doorway creating the feeling of an old 'ruin'. The effect in the architecture of the structure will be that of a newer cob building, built over 'ruin' of an old adobe block building.

The idea to use adobe block in the cob building came from knowing that I had adobe bricks on site since the year 2000, the year the out-building (pump house) was constructed.

I wanted to use materials already on hand in construction of the studio, so I had a creative challenge to design those adobes into this cob building aestheticly.

All these years since 2000, approximately 120 adobes were left over and kept under protective wrap - waiting for a suitable application. That time has come.

Cob Walls Start to Rise

Finally, after a few years of meticulous work on the stone stem walls, cob is being applied to those walls.

My soil is extreme clay and I'm using this same soil for the walls. What's cool is that i'm using the same soil removed during the excavation of the hillside; that this studio is now bermed (see earlier blogs).

So the excavated clay soil becomes a 'local' resource used in making all the walls. If you include the cost of the excavation, and the straw used with the clay to make the 'cob', it's about $1,000 in primary materials. With that you get all the structural walls that also act as a thermal mass system. So the design of thermal mass in this structure, gets me a free heating and cooling system by utilizing the daily temperature cycles that make up a desert climate. This is how to extremely leverage $1,000 into the substantive basis for a comfortable and sustainable living environment.

Machine & Materials

Both placement of the clay screening area and the mixer were considered in relation to the distance the wheel barrow loaded with 'cob' would need to be hauled to the wall locations.

Some readers of this blog may object to the use of a gasoline powered machine in the construction of a 'natural' building. I can appreciate that thinking. From my perspective, the machine will assist in getting the building done and put to productive use sooner. Especially since this building will be my office and creative project space. Nothing can be more important for me now, then that space.

Nature's Stained-Glass Window

As preparation continues to begin the cob walls, I needed to prepared a large Honeycomb Calcite stone slab for placement placement in the east wall.

The stone needed polishing on the flat surface side (shown in photo), that will be facing toward the interior of the room.

The opposite side of this stone is the original outer surface, which is right now a frosty-white. Later I will sand-blast the outer surface of the stone to remove some of the stone's 'skin'. That will allow more light through, enhance its translucency and thus create the stained-glass window effect.

Cob Preparation Project for a Sunday Afternoon

Fastening A Window - Preparing for Cob

This is a window I'm adding on the northeast facing curve in the wall. I wanted this window up-high, so to provide cross-ventilation for the large room of the studio space.

I'm using rebar, coming-up from the stone stem wall, to provide support for the window (frame). I used a section of bamboo, secured to the the rebar, as the securing base of the frame. The top of the window frame is level with the top of the door frame, just next to it.

Click on photo for an enlarged view

I have anchor bolts extending-out from the frame (in photo shown coming out from either side of the frame). These anchor bolts, along with the bamboo and vertical rebar supports, will all be "cobbed-over" eventually. "A support within a support" So-to-speak.

Window Sills

With a stem-wall height of approximately 3-feet, the rough frames for the south facing windows are essentially just above the wall height. See photo to left (before shot).

Anchor bolts were cemented into the top of the stone wall to secure the rough window frames to the wall. I decided that instead of simply cobbing under the windows and plastering (a potential future maintenance hassle), that I would just continue the stone masonry up to the bottom of the window frame, creating a attractive and maintenance-free surface.

I use old bicycle tire tubes stapled to the bottom of the window frames (not shown) to create a 'seal' between the stone and the frame. This keeps water from leaking in from the sill.
The photo above shows completion of the first sill (inside looking out). The sill on the outside will slope slightly down in order to keep rain from pooling and working its way under the sill.

Smaller flat rocks were collected for this phase of the building project. I initially thought this part of the stone work would be a real pain; but seeing how the sills add a finished look to the stonework and the creative aspects of fitting stone, is making this task quite rewarding.

(Note: Click on any photo in this blog to enlarge)

Retaining Wall

The stone retaining wall for the western berm was recently completed. It rises to 8-feet high, which is about 1-2 feet higher than the earth on the western side of the studio building.

Eventually, the wall will be extended further (north) along the excavation to become the western wall for new (future) buildings.

For now, the wall was constructed to this size in order to protect the studio from a possible cave-in of the earthen berm during heavy summer monsoon rains.

The area between the retaining wall an the studio as shown in the photo will remain outdoors as part of the 'hacienda' concept envisioned for the several additional living structures planned for this overall design.

The second photo shown here is a close-up of the wall showing details of the stone masonry.

As with the rest of the studio stem-walls. All stone has been obtained locally in dry washes and nearby mountains.

After two years, the stone work is wrapping up. There still are some finishing touches before the 'cobbing' will begin.

Backfill of West Wall

Preparation for cobbing continues. By backfilling the west wall, accessibility is now improved.

Due to high clay content of my soil, I've found it practical to lay-down about an 1-inch thick layer of gravel to not only keep erosion from rain water in check and make walking and hauling materials easier around the structure. Also, the gravel helps but keep mud off shoes after rains.

The gravel was shoveled and hauled by pickup from a nearby dry-wash. It's hard to tell from the photo, but the 'pitch' of the backfill is such to move water away from the buildings toward the mesquite trees just to the south.

Honeycomb Calcite for Cob Wall

I plan to place in my cob walls, a beautiful translucent orange-golden colored stone called Honeycomb Calcite. The stone is quarried in northeast Utah as boulders, then cut into slabs, cored to make cylinders or scuplted into various shapes. Over the past 7-years I have been selling this stone as a side business after incorporating small slab in the wall of an adobe building I completed (see Adobe Out-Building).

You can see from the photos in the link for the adobe out-building, the stained-glass effect with the stone placed in the wall is fantastic. After the adobe out-bulding was completed, I fell in love with the stone and I now plan to use it in all my natural buildings.

The slabs shown in the photo above weigh up to 200 pounds. They have not yet been polished to bring out the full color and texture. Only one or two will be placed in the studio walls, the others will be sold to artists, sculptors, and other natural builders.

I need to select the Honeycomb Calcite slabs I will use in my studio before I begin the cob, so I can devise a mounting method to insert the slab and build the cob wall around the stone. Stay tuned to this blog as building progresses.

Solar-Gain Room Stem-Wall Completed

Work on the solar gain room stem wall is now complete. The wall looks taller than adjacent walls because the grade of the land slopes southward. However the interior wall height will be about 2-1/2 feet high from the finished floor level (you can see a small 'stake' on the above photo - right side of photo - that was set in with a surveyor's level at what will be the finished floor height).

Solar Gain Room

The stem wall being constructed here is for an area that I'm calling the "solar gain" room. Facing south, there will be large windows on three sides and a stone floor to absorb solar radiation during the winter months. Once the building is complete a french door separating the solar gain room and the studio, could be openend to allow heat to enter the main studio space. At night, the french doors can be closed and the solar gain room will act as an additional insulating buffer from winter nights that temporarily get down into the 20's and low 30's.

The reason why the stem wall for this room was not completed earlier was to facilitate construction access. This room is a bulge on the south side of the building. If this area was constructed earlier, access to the south & north side of the studio for hauling rock and other material would have been difficult. Trees, cactus, yucca and the grade of the land make access to the south side very tight. Now that the stem walls for the entire studio are essentially complete, construction of the solar gain room has begun.

Technical notes: The stem wall, like the rest of the studio rests on an 18-inch deep rubble trench footing (filed with 1"-3" dia river rock). However, the wall for this area will be only 16"-thick, compared to the rest of the studio where the walls are 2-feet thick.

Stem Wall Progress

Except for a small 'solar gain' room that will be added to the southeast corner of the studio (top left of photo), the stem wall is almost complete.

The right side of the photo shows the retaining wall buttressing the earth to the west,
sufficiently completed. But as time allows, that wall will be extended to eventually form the basis for new buildings.

Room Passage Completed

These photos show two views of the newly completed stem-wall section for what will be an Anasazi-style archway between the two main rooms of the studio (See Anazasi Arch entry for a historical view of how this passage will look completed.)

West Wall Above Earth Height

The west wall of the studio's 'kiva room' is now at sufficient height above the earth berm. Not shown, but extending north (from top-right of photo) is the 8'-high stone wall retaining the earth along the western cut of the excavation. Once a portion of the retaining wall is complete, work will move to completing the 'Anasazi Arch' (see blog archives for discussion) that will connect this room with the larger studio room. And finally, the solar gain room off the southeast side of the studio will be completed in september.

From that point preparation for the 'cob' (straw/clay) walls will begin.

Stem Wall Nearing Completion

This photo shows an overview of progress on the stone stem wall as of June 12, 2007. The west wall (right side of photo against the berm), has reached to top of ground height. It will need to extend about 18" higher (above ground height), before construction of the earthen walls begin.

The western retaining wall that extends north from the circular room, still has a way to go.

The stem wall for the solar gain room on the south side of the structure (top-left in photo), will be completed last, so not to impede easy movement of stone and material needed to complete the stone work on the west side of the studio.

With the summer monsoon season on its way soon, the studio is ready to take-on the expected heavy rains!

Backfill

Following the application of at least 12" of gravel over the drain pipe, 6-mil plastic was laid on top of the gravel and the entire disturbed area was backfilled. To facilitate water drainage away from the stem wall, the soil was graded to slope away from the building. As the backfill was in progress, a tamper was used to compact the soil to help prevent settling (although some settling is expected).

Once the backfill was complete, about 1" of sandy gravel was added to the disturbed area. This was for practical reasons. The gravel will help: 1) Keep dust from kicking-up during high winds. 2) Keep excessive mud off boots during the upcoming summer monsoon season. 3) Reduce soil erosion during rain.

Completion of the backfill will improve building productivity because the stem-wall on the west side (the berm side), was getting too high to reach. Also, working in the narrow confines between the earthen berm and the stem wall was a safety issue (cave-in, trip/fall).

Footing Drains

My desert location receives approximately 15-18" of rain per year (if we're lucky!). In the summer monsoon season, heavy rain falls during thunder-showers. The key to keeping water away from the studio will eventually be proper finished grading of the soil, in order to slope away from the stone walls.

This location does not have issues with waterlogged soil like other parts of the country; where collected water between the foundation wall and the soil is subject to kind of a hydraulic pressure that in effect, forces the water through cracks in porous foundation walls. However, even in the dry desert, building codes and good practice recommends installing a provision for water removal around the footings/foundation of most structures This prevents water from seeping through walls into living areas and water saturated soil from undermining the structural integrity of the footing/foundation.

The first step was to waterproof the stone wall that will be buried in the berm. I decided to try an elastomer (rubberized) roof coating. I applied two coats (fill & finish). In the old days, I used 'tar' to waterproof foundations, but I'm trying to avoid petroleum products in this structure; and also, tar is very messy. Will the elastomer coating work for the long haul? I don't know, but the instructions said it can be applied to stone & masonry. It has a 10-year rating for roofs; and the coating won't be subject to UV sun damage as it will be buried in the ground.

As the photo above shows, the ground was leveled and on it was placed a 6-mil plastic ground sheet to prevent the clay soil base from clogging the pipe. The plastic pipe is perforated, and the holes were placed down to draw-in any water collecting on the plastic. The pipe was leveled. To get around the circular shape of the building I used 45-deg elbows and connected short sections of pipe (as illustrated in the photo).

The photo to the right is kind of a cross-section of the footing drain project, showing gravel around and on top of the pipe, followed by a top sheet of plastic to keep the clay soil that will be used for back-fill, from working its way down into the gravel over time and clogging pipe (click photo to enlarge).

Also in the photo you can see rigid foam insulation (R2.9), applied against the stone stem-wall. This insulation will provide a thermal break between the earth berm and the building.

Provision For Electrical

All electric lines were embedded in the stone stem wall. Outdoor direct burial #10-wire (30-amp capacity) was used. Placing electrical boxes in a stone wall was a challenge; but the height of the wall (2-1/2' - 4' tall) necessitated such placements.

Also notice on the right side of the photo, a piece of plastic electrical conduit (capped). This conduit extends through the wall on the south-side of the building, for the purpose of future telecommunications hookups or antennas.


The five electrical circuits terminate in the future solar equipment/battery room.

Not shown are two (2) additional underground conduits; installed with the purpose of providing electricity to future adobe buildings that will compliment the studio as part of this hacienda-style site layout.

Rebar & Bamboo

In order to help secure the forthcoming cob walls to the stone stem wall, vertical rebar was placed in the stem-wall during construction of the wall. Lateral support was provided by the use of bamboo poles. Bamboo is both a strong, renewable natural resource; and was provided by a local grower. For curved corners, short pieces of rebar were hand-bent and secured to the vertical rebar using wire.

Also note that the stone stem wall is concave at the top so that the cob mix will 'key' into the wall for additional lateral stability.

First Quarter Progress

Progress photo taken at the beginning of April 2007. Note on far front-right of photo, the stone retaining wall that will rise 6'-7' high on the west side. The area just to the left (east) of the retaining wall will be an open-air area of the hacienda, providing needed afternoon shade for sitting outside.

The only wall construction remaining is the retaining wall and the west side of the kiva-library room (top-right of photo).

Kiva Room

This photo looks west from the main studio area into the kiva library. Notice that on the left side of the photo the pass-through wall height is complete; but the right side is not. This is for practical reasons: If the right-side pass-though wall was completed, I would not be able to get a wheelbarrow through!

Also, from the top of the photo, you can see the earth that the structure will be bearmed against. The stem wall on the west side of this room will need to rise at least 12-18" above the berm, before it is complete.

Year End Progress

As 2006 draws to a close, I wanted to post this photo as a snapshot of where I'm at to this point.

There is still a lot of stonework to do, but my calculations show that I was masoned 35-tons of stone so far. This figure includes the stone, sand, gravel, slaked lime and Portland cement.

I estimate that the stone stem wall will use 50-tons of material before its complete, and I then can begin the adobe (cob) walls that will define the stucture.

My back is doing fine :) Happy New Year!

The Stone Pit

Work continues on the studio. Now winter time is here and like the summer, productivity is impacted. Due to the 3,650-foot elevation of this site in Arivaca, night time temperatures dip regularly into the 20's if not the teens. Water hoses freeze, days are short, and who wants to get out of bed into that cold anyway?

But work presses on and 2007 offers the opportunity to continue this giant stone sculpture, that will eventually become my art studio.

Rough Openings

In order to secure rough door openings to the walls, I first used my builder's level to set concrete pavers in cement at the height of the finished floor. The rough 2"x6" door bucks were then set on top of the pavers, leveled and plumbed into position. The rough door openings were fabricated to the outside dimensions of doors already purchased for this project. Rough openings are made at minimum 1/2-inch bigger on all sides to allow for the finished door to fit the rough opening and for shims necessary to level the door in place.

In order to secure the rough door buck into the stone, I drilled a hole in the wood - the diameter of the bolt - and inserted the 8"anchor bolt (see above photo). Also notice in the top-left photo of the collage, that I counter-drilled a larger diameter hole that does not go all the way through. This allows for a large washer, nut and leaves room for a 3/4" socket to be inserted to secure the nut. The nut is secured once the entension part of the anchor bolt is cemented into the stone wall against the door frame.

The bottom-right photo in the collage shows the finished wall build around the the rough door buck. Two additional anchor bolts will be placed vertically, on each side of the frame of the rough buck, as the cob is applied to the wall on top of the stone stem wall.

Anasazi Arch

During my travels to Chaco Canyon and other Anasazi ruins throughout the Four-Corners area of the southwest, I noticed in several locations the design of what I call the "Anasazi Arch" (see photo to right). It's essentially a "T"-shaped passage between rooms. In the case of this photo the passage leads from a room into a ceremonial room of the great Kiva known as "Casa Rinconada" at Chaco Canyon, New Mexico.

I plan to incorporate an "Anasazi Arch" that will connect my studio work room with the library room.

The photo to the right shows the begining of the "Anasazi Arch" in the studio with a view looking toward the main studio room behind me.

The stone work is in its early stages, but the right side of the passage shows the detail work to this point.

Taking Shape

The photo shows progress after a couple of months of work. Summer heat and monsoon rains effected productivity for obvious reasons.

If you look closely at the ground in the photo you can see the ground in and around the studio with a layer of gravel. In order that I could work after rainstorms without my feet getting stuck in the clay mud. I made six trips to a nearby dry-wash and filled the bed of my truck gray-colored gravel.

With regards to the summer heat, there was nothing I could do about that :)

3-Dimensional Jigsaw Puzzle

I'm learning as I go, but one thing is for sure, these stem walls are solid and look great. As the walls rise out of the ground, there is an artistry that emerges and your building feels like a giant sculpture.

Some of my natural bulding friends have asked me when will I stop with the stone wall and begin the earthen 'cob' phase of the building process.

My answer to that question relates both to structure and aesthetic design. The stone-footing at minimum, needs to support the massive adobe (cob) walls that will rest on it. In addition, the west side of the studio that will be bermed into the hillside, needs to be all stone until it reaches a height at least one foot to 18-inches above ground level. This will keep the splash of rain hitting the ground from hitting the earthen wall (that will eventually be lime plastered). Also, the stone stem-wall will deter termites from gaining access to the earthen walls.

Finally, the transition from stone to the earthen wall will achieve a significant visual aesthetic for the structure. An example, would be the straw bale house of a friend in Alamos, Mexico, where the stone stem-wall concept was employed. (see photo to above).

The difference in my design besides the use of 'cob' instead of straw bale, will be that the height of my stem-wall will vary along the course of the structure - like the rolling hills of my surrounding landscape.

Progress Photo

Stone Stem Wall

Using locally sourced stone pulled from nearby mountains and dry river beds, two-foot wide masoned stem walls have begun to rise from the top of the rubble trench footing. My technique is to place and mortar stone along the inside and outside of the trench and then 'infill' with additional rock and mortar, thus tying together both sides of the wall.

I am planning to lay a first course around the perimeter of the studio and then work vertical from there.

Rubble Trench Footing

The "floating footing" or "rubble-trench footing" is an alternate approach to a building's base foundation for heavy clay soils, as opposed to simply pouring concrete into a footing trench. Clay soils are expansive and when wet could possibly put a lateral stress, or cause heaving to, a standard poured concrete footing.

In the concept of the 'floating footing', the typical 'in-ground' concrete footing is replaced by 1"-3" (rounded) river rock. The footing channel for my building, is 18"-deep and 2-foot wide. The footing was hand dug and a surveyor's level was used to ensure a slight pitch for drainage of the footing, leading to a pipe at the southeast corner of the building. The channel was lined with heavy-duty plastic to facilitate water drainage and keep the ground directly under the floating footing from getting saturated during heavy rains.

The river rock was compacted with a tamper and eventually brought up to grade level. On top of the floating footing will be a massive 2-foot wide 'stem-wall', made of large stone masonry. In most places this wall will be 2-foot wide.

I have been curious to employ this method ever since I heard Frank Lloyd Wright used a floating-footing for construction of the Imperial Hotel in Japan in 1916. This building subsequently survived a severe earthquake without major damage. The theory is that since the building rests on the surface (on top of the rubble filled trench), when an eathquake stikes, the rubble-trench slides under the building when subject to the lateral force of the earthquake.

The foundation of a building is critical to maintaining the integrity of the structure. It needs to be strong and the appropriate size for the building so the structure won't settle, buckle, or spread apart. Please note that the "floating footing" system is somewhat experimental and not appropriate for sandy soils or sloping terrain that can be eroded to the point where the rubble-filled trench would be exposed and compromised. Consult an soils/structural engineer if necessary for your project.

Provisions For Solar Electric

Doing the grunt work early on makes the project go smoothly and the finished building look well planned and designed. The time to lay in utilities (water, gas, waste water, electric, phone serivce, etc) is when you're doing the footing/foundation. Neglecting the proper installation of these essential services now, means later you will be drilling through finished walls, have exposed pipe & wires to the weather and UV damage; not to mention it will just be ugly.

In the case of my art studio, I will only be using electricity. However, I plan to 'rough-in' black pipe for supplemental propane heat if the bulding's thermal performance upon completion requires it. I also provided conduit for phone or antenne lines if wireless options are not available.

The photo shows 2"-gray electrical conduit extending down the exposed excavation to what will be the utility room of the studio. This conduit will contain the main DC electric load wires from the solar photovoltaic system that will be installed later, on the elevated land to the west of the studio. Not shown are two additional underground conduits that will someday bring electricity to other small ancillary buildings (not yet constructed) that will be adjacent to the studio to complete the hacienda-style layout of the studio compound.

Gravity Drains

It is critical that rubble-trench footings be properly drained; especially since heavy clay soils are expansive and could put stresses on the footings. Wet clay soils could also result in excessive settling of the structure if not kept dry.

I used a builder's level to pitch piping for a gravity drain to remove any water that could accumulate in the rubble-trench footing. The south sloping land away from the structure provides a natural contour for water removal.

The entire footing trench will be lined with heavy-duty construction grade plastic prior to being filled with 1"-3" rounded river rock.

The studio footing gradually slopes (1" per 7-ft) from the northwest corner toward the southeast corner where the drain pipe is located. Any water drained out the pipe will irrigate a mesquite tree grove on the north side of a dry wash.

Pick & Shovel

I began work by digging a 2-foot wide, 18-inch deep 'footing' trench, that made up the footprint of my studio design. The compacted heavy clay soil of my land is ideal for digging trenches with firm side-walls. In another building I constructed on my property; I created a concrete footing, simply by digging a trench in the clay, set up reinforcing bar, then poured concrete directly into the ground. No form-work was necessary. This method saved both time and money.

Refering to the photo, the circular room will be the library/office. The large oval room will be the primary creative space for digital-film post production. The rectangular space to the right will contain the batteries & controlling equipment for the building's solar-electric power. A division in the same room will provide storage space for the studio. To get a feel for scale, the building will be approximately 35-feet by 25 -feet in size.

Stake In The Ground

Since it has been about 8-years between the time I purchased my land until I started the studio; I used that period of time to observe the land and plan both the art and the science behind the location of the first structure. I knew once the excavator arrived to clear my building site, there would be no possible way to change my mind regarding placement of the cob studio.

My cob art studio will be the first of several solar-powered earthen dwellings, making-up a hacienda-style placement of living/workng environments.

The photo in this blog shows the completed excavation for the studio. I chose to locate the studio in a berm for several important reasons: 1) The clay soil excavated will become the primary building material for the structure. 2) The west side of the building will be against the berm, thus keeping the afternoon summer sun from baking that side of the building. 3) All structures built in the mound will seem to blend into the environment, as opposed to sitting directly on top of the land and sticking-out like a sore thumb. 4) Sounds that seem to travel unobstructed over long distances in the desert, will now pass over top of the buildings; resulting in quieter living/working environment. 5) I will just look cool.

The photo in this blog shows the completed excavation. The left side of the photo is south; the right side of the photo is the north side. The excavated profile of the land running across the photo is the west side and has an elevation of approximately 9-feet at its peak height. My cob studio will incorporate a passive-solar design; with a majority of the windows facing south in order to optimize solar heat gain in the winter. Most bermed buildings have their north side against the earth. However; since the earthen mound on my property runs north-to-south for approximately 100-feet, I decided that the summer sun in the west would be more of a challenge to creating a comfortable living space than the potential cold of the north side: Therefore, I will be 'berming' the west side of the studio.

Since I'm starting out with the studio at the south end of the mound, the current idea is that the north side of the building begins the courtyard. the courtyard will extend towards the north until the next series of structures is built.

Local Resourses

When I was in the process of chosing a land for my art studio, the availability of natural building materials on or near the site was an important consideration in the purchase. As the photo shows (starting at the top-left clockwise); the land I selected, has many small rocks on the surface that I use for a variety of purposes: Gravel fill, drainage channels, aggregate for concrete, pathways, etc. Testing the soil revealed ample clay - ideal for making adobe, cob and earthen plasters. The piled stones in the second picture were culled from mountain washes on nearby federal land; and used for the construction of stem-wall footings. A heavy metal screen for sifting clay and river sand was purchased from a local metal dealer, who obtained the heavy steel mats from an old mining operation in the area. The last photo shows a dry wash on my property where sand for application in cement mixes, lime plasters and other building uses is obtained. Flash-flooding that occurs each rainy season, replenishes the sand, creating naturally occuring sustainable resource.

The use of local resourses for natural building materials not only saves money, but reduces planet energy consumption associated with the use of excavation/loading equipment, rock crushers, and trucking materials long distances to the project site.

Image for Design

I have spent several years trekking to Anasazi ruins up in the four-corners area of the southwest, looking for design inpsiration for my art studio. However the light-bulb didn't go off until returning a few months back from Chaco Canyon.

On the 6-hour drive back to Arizona - assisted with a cup of hot coffee - I had plenty of time to think and generate ideas from the new information I had gleaned during the trip. I arrived home at 11 p.m. and with work the next morning you would think I would have crashed for the evening; but instead I decided to watch a movie! It was imagery and sound film by Godfrey Reggio called Powaqqatsi (Hopi meaning “Life in Transition”). The film is a montage of images about life in the Southern Hemisphere and how globalization and technology is affecting the hand-made way-of-living for these people.

In one 6-second scene in the film, an aerial fly-over view of a primitive farm in Kenya, Africa is shown (Refer to photo). Hedges in circular and curved-line shaped patterns bordered the farm, houses, outbuildings and animal pens. I was fascinated by the aesthetic quality and ‘organic’ abstract design of this dimensionality. I froze the image on the TV; took a digital picture of the screen; then loaded the image on my computer; traced the hedge outline in PhotoShop; and printed a hardcopy to plan from. Then I went to work at my drafting table with an architect’s scale, and before I knew it I had designed the layout for my studio. It fit the land; it met my space requirements and the design mirrors the architectural style of Anasazi . Most importantly, the layout was ‘buildable’ from a practicable standpoint. It was all there. All the design aspects and aesthetic details I have been struggling with for several years reached convergence and made itself known.

I think back now to the film. What were the odds that year’s ago cinematographer would fly-over a farm in Africa and put it in a film? Then I would see this image on a video and design a house based on the planting of hedges around that farm? In some way it seems random to me and in another way the saying: "Chance favors a prepared mind" seems appropriate. The whole process is like writing a poem.

Ancient Building Technologies

When first thinking about designing a solar-powered earthen studio for my filmmaking and other multi-media art, I was highly influenced by my visits to Chaco Canyon in New Mexico. I wanted to think like an Anasazi in order to adapt dwellings to what can be harsh climate conditions in the Sonoran desert of Arizona. Although the walls of the buildings at Chaco Canyon are stone, my material will be "Cob" which is a mix of straw and clay soil. However, I plan to build a stone 'stem-wall' out of stone for structural and aesthetic reasons.

Cob lends itself well to building irregular shapes, such as: Circles, Curves, Ovals, etc. I wanted my studio space to have flowing curves and a circular room similar to a ceremonial Kiva. (Photo by Barton Santello: Passage between rooms - Pueblo Bonito, Chaco Canyon)

The Man Behind The Plan