April 02, 2018

East Wall - Toward Final Height

It's been over a year since last working on the Studio due to competing priorities.  However, a push to complete the east wall up to bond-beam height has commenced.  This wall makes up the larger room that has yet to have a roof constructed.   Once this roof is completed, finishing work on the interior can begin.  

The roof over this part of the structure will be a huge project itself.  But for now - one step at a time.

July 06, 2017

North Looking South View

There is still much work left to do on the cob studio - like a roof over the large room. However, as the summer monsoon season approaches here in southern Arizona, it's a good time to take a break and catch-up on maintenance and repair around the property. 

The photo below shows how the cob studio looks from the north.  The building blends with the earth, with the dome prominent.

One of the side projects I worked on this spring was a second Gabion (check dam) in my dry wash.See the blog post here:  http://gabion.blogspot.com 

November 17, 2016

Scratch Coat - Earthen Render - Inside the Dome

A rough (scratch) coat of earthen plaster was applied to the inside of the dome in preparation for a final lime wash that will follow (see below for photo of a section of the work).   Once completed the scaffolding can be removed from the inside of the 'dome room' and I can move to the next task in the construction of the studio.


I have a book on earthen plasters but never got to reading it.  My considerations for the rough-coat was that it had to be thinly applied so not to flake-off and that the materials could be sourced from the property (no cost solution).  

The photo below shows the three ingredients I chose.  From left: Sifted sand from my dry wash; Calcium Carbonate (CaCO3) which is a byproduct from my cutting calcite as part of a stone business I have ( www.stoneproducts.biz ); and sifted clay soil that i have been using all-along to mix the 'cob' for the building itself.  Think of both the calcium carbonate and clay as the binder and the sand as the aggregate to both add texture, strength and resist cracking.

For the mix I used one part clay, one part calcium carbonate and two parts sand.  The mix was not tested beforehand, therefore in hindsight I observed that should have used much more sand; at least four parts (instead of two) to prevent cracking that you can see in the close-up photo below the video.  Water was added to create an earthen slurry.

The video below shows the consistency of the mix.  I wanted a wet mix to better absorb and thus adhere to the inside of the clay dome.  But I did not want the mix to be overly 'runny' because I was using a gloved-hand to apply to the existing cob ceiling, instead of a trowel.

I prepared small sections of the ceiling to work on at a time.  I would wet-down small 2'x2' sections since the cob wall that is mostly clay would absorb the water quickly. Actually, I would keep wetting the wall (with a misting nozzle) until it was super-saturated, then hand-rub-in the earthen mix as a thin layer to create a good bond.  See short video showing me applying the render inside the dome.

The photo below shows the rough coat after application and drying.  There are many cracks due to insufficient sand, but since I'm going to apply a finish coat (lime wash), hopefully most of the cracking will not be noticed.  Actually, I want more of a rough-textured dome ceiling and the cracks are part of that look.

I was curious to see what the dried rough coat would look like with the addition of the Calcium Carbonate.  Since the Calcium Carbonate is rock dust and is not 'fired' like slacked-lime like you buy at the hardware store, I was not expecting be benefit of the absorption of carbon dioxide (CO2), which would happen with slaked-lime.  In that case the absorption of carbon dioxide from the air back into the lime after application, would essentially turn the slaked-lime back into limestone.

In my case, the un-slaked Calcium Carbonate byproduct from my stone business, acted more like clay - binding to it - and creating a good bond.  So in general, I'm happy with the rough coat.


Below is a bonus photo showing the scaffolding 2-sets, that helped create the platform which to work in the dome's ceiling. Notice in the foreground the 3-foot thick rock stem wall which supports the thick cob-walls of the interior passage.  Also at the top of this photo is shown the 8-inch diameter Mesquite wood beams that support the roof and dome above.

August 17, 2016

Status Shot - August 2016


Standing at the NW side of the studio I took this 'status' shot after relocating the scaffolding to the East side of the building in order to complete the last 16-inches of cob, in preparation for the last roof line over the main room.

July 02, 2016

Pouring the North Landing


The photo above is the completed 'landing' made with site-mixed poured concrete.  I added brown coloring to the mix to give the concrete a conforming tone.

The first step to creating a 'landing' was fabricating a rebar pattern to help re-enforce the concrete and secure it to the top of the wall.  Additionally, just below the rebar you will see where I added a strip of one-half inch thick styrofoam, as the first step to building a form to retain the concrete .  The Styrofoam in the form, acts as a spacer that when completed will create a 'lip' extending the concrete over the wall

The photo below shows how the form fabricated to retain the concrete was added using Masonite, wood stakes and 4"-deck screws.  I've been reusing Masonite forms made from 4'x8' sheets, cut into 14"-wide strips.  The wood stakes with two deck screws each - drilled into the cob wall - is amazingly strong.  This is the form method I devised for bond beams and top-caps poured along this curved building.

Approximately 300-pounds of concrete made up of Portland cement, sand and gravel, along with brown concrete color was mixed 'on-site' for the pour.  Not quite visible on top is a channel that was contoured during the work to direct water from the sides of landing, inwards; toward the channel, so that channel can then drain any water out to the west side of the structure. 

The narrow (neck) of the landing along the west wall makes a sharp curve, so i used more of the wood stakes to wrap around, thus extending the form as necessary (photo below).

June 19, 2016


The photo above shows the final application of elastomeric coating (Maxi-Stretch) to the dome.  The manufacturer (Ames Research) pre-colored the polymer to a light tan shade.

I decided to continue to move away from a traditional lime plaster exterior rendering due to the fact that all the natural builders here in Arivaca have had no long-term success with keeping the lime plaster from separating from a cob base wall.  This is due to the daily 40-50 degF temperature swingshere, that cause lime plaster to expand and contract at a different rate than the underlying cob wall, thus essentially separting itself from the cob wall. 

In the traditional sense, earthen structures need to breathe.  Therefore, I plan to use an earthen rendering for the inside of the dome for that purpose. Here in Arizona, the climate is mostly very low humidity, therefore excessive moisture in not an issue compared to other regions. 

The coating in the photo above was the intermediate coating of liquid rubber.  The trade name is Blue Max.    It's really cool to paint-on your own rubber roof.  Note that Blue Max is not UV stabilized and requires a top coat of elastomeric such as the applied Maxi-Stretch

I took this photo knowing I would need to show the layers of applied coating to descibe the waterproofing concept for the dome.  In the photo above to the right, two applications of Super Primer by Ames Research, which acts as a sticky base coat which hopefully will securely adhere to the straw/clay mix and provide a base surface to build-up the other coating.

Then again as discussed above, I applied to coats of liguid rubber (Blue Max), followed by 3-coats of elastomeric.   This brings the weather-proofing to seven total coats for the dome.

Please note that this process of appling a painted-on rubber coating onto cob (straw/clay) is EXPERIMENTAL, with the thinking that it cannot be any more of a maintenance burden that having to replace a lime plaster rendering every two years as has been the case with other adobe building I have constructed.

Also note that these high-tech coating are non-toxic and safe for water-harvesting.

May 31, 2016

Dome Fully "Cobbed"


 Nothing like a completed dome!

The photo above shows the inside of the dome looking up from the scaffolding platform inside the circular room, upon which the dome was built.

The photo tends to 'flatten-out' the dome shape.  Working that last top portion was tiring for my arms reaching up to shape the drying cob.  

May 23, 2016

Bamboo Supporting Strips Added


As mentioned in the previous post, as reaching the top of the dome nears, I needed to add strips of bamboo inbetween the rebar support (see photos above).  At this point, I simply grabbed as much cob as I could and placed it on top of the bamboo strips and rebar then shaped accordance with the evoliving shape of the dome.

In the top photo, I'm working from the inside.  If you look closely, especially to the left of me, you can see how the cob has slumped and fallen in on itself somewhat.  I just have to removed the excess and place where it's needed and just keep working it until the inside surface is shaped uniformly.  

May 12, 2016

Closing In


I'm at the point in shaping the dome where the angle inward begins to get pronounced, therefore, I'm making my 'cob' mix stiff so it doesn't slump too much and fall in on itself. 

At this point I have had to raise the scaffolding so I can comfortably reach as I move around the dome to work.

April 18, 2016

Scaffolding Necessary to Complete Dome

I took a day to arrange the scaffolding in order to work comfortable at the top of the dome.  The photo may suggest a precarious situation, but actually the platforms are stable.

The dome has changed everything with respect to the architecture and imagination of the structure.   And the inside ceiling of the dome will open possibilities for finishing renders and lighting.   I hope to complete the dome before the summer monsoon season around the beginning of July.

January 18, 2016

Dome Progress Update

Work on the dome has finally resumed after a failed well-pump needed a few months to order and install.   As the dome rises and the cob needs to be hauled up scaffolding, progress takes longer, but the winter days here in southern Arizona are beautiful - sunny in the low 60's - perfect weather for cobbing.

I'm using the rebar skeleton as a guide to shape the exterior of the dome. It's all by eyeball. The thickness of the dome wall is approximately 1-foot thick.  When shaping the dome, I parallel the rebar.  But as I near the top and the angle change is more pronounced and the challenge to shape the dome uniformly increases.

December 15, 2015

View of South Side


With winter here and leaves off the trees, a photograph of the south side of the studio can be taken.  Progress on the dome (top-left) has stalled due to a problem with the well pump; but hopefully it will be resolved soon!

September 13, 2015

Dome - Mid September 2015


I took a moment to photograph the dome as the late summer's monsoon season continues to resurrect itself  into September. I took these images for a status update on the dome: But now that I look at them I noticed the light and an approaching storm in the sky

July 28, 2015

Bond Beam & Dome Progress

A section of bond beam was poured (see photos below) on the wall supporting the east side of the dome.  This was a necessary step since the size/shape of the dome on the east side extended slightly onto the bond beam (photo below)


As can be seen in the photo above, the 12-14" thick 'cob'(clay/straw) walls of the dome provide incredible strength.  As the dome rise the walls will be made thinner and with more straw to reduce weight.

The photo above shows the freshly poured bond beam on the east side of the dome.

July 12, 2015

Cob Dome - July Update


The 2-inches of rain so far kicking off the monsoon season here in southern Arizona has barely put a scratch on the progress of the cob dome.  Work makes slow progress in the summer due to unpredictable thunder-showers, heat, mosquitoes and mud.  

The photo above shows preparation for a 'bond-beam' pour for the wall making up the room to the east of the dome (not shown).  The photo shows the rebar in the trench where the concrete beam will be poured.  Note the 'form-in-the-sky' shown to the left in the photo, has a strip of flexible 'Masonite' board as the left side of the trench.  The Masonite is held in place by wood - short 1"x2" (wood stakes) and 4"-deck screws.  The cob holds these long course-threaded screw really tight.  So much so that it's going to be retaining the concrete as it's poured in the form.

Once the bond-beam is poured.  I'll be able to use it as a working platform for the east side of the dome construction.  

Just a note that the thickness of the wall on the left side of the photo between the main room and the dome is a massive 3-feet (lots of cob!).

May 17, 2015

Dome Rising

Took advantage of temperatures dropping to 70-degF to work the dome.  With the assistance of Nick Dunn whose currently over at Forever Yong Farm in Moyza; we hauled over 1,000 pounds of cob up scaffolding on Sunday, to add another layer.


Photo above showing the dome's outlined shape - structured with rebar. 

Close-up detail of sculpted cob rising off a concrete bond-beam base, curving in parallel with the dome-shaped rebar.

January 25, 2015

Next Step - The Dome

I took this photo after thinking about the 'dome building' phase of the project which I plan to work next.  The dome is a shape that's captured my imagination in studying Middle Eastern and early cultures.


January 22, 2015

Exterior Render

I have been amazed at the resiliency of cob to hold-up in the rain.  In Arivaca, the rainfall totals on average per year are about 15-inches.  This past year (2014) we had over 20-inches.  Some of the walls of this studio have been exposed to the elements for 5-years and the photo below shows a typical section of exposed wall.  


The downfall with the traditional lime-plaster here in Arivaca where temperatures fluctuate more than 40-50 degF a day, is that it eventually separates from the wall due to differing rates of thermal expansion between the plaster and cob wall.  And thus every couple of years the entire building requires new application of lime plaster.   

So I'm developing an experimental method, I hope will be over time will require only light maintenance. 

The photo below shows a thin layer of cob (clay/straw/water) mixed with colored elastomeric, that I have been experimenting with as an alternative to lime plaster.  I'm hoping the exposed straw from the eroded wall will help grab and hold this thin exterior cob (clay/straw) render.  This approach is a mind-set change from the traditional lime-plaster render, that although breathable, provides a uniform 'seal' to cob/adobe buildings.  

Last summer I applied a test coat of this mix on parts of the south wall to see how it would hold-up during the summer monsoon season.  The photo below shows how the cob render with added elastomeric (about 1-quarts per 1/2 wheel-barrow of cob), did exhibit some erosion; but I don't think I put enough elastomeric in the summer test mix.   So going forward, I'm adding 2-quarts of elastomeric to the 1/2-wheel barrow of cob.

The photo below shows most of the east side of the building rendered, with the just a quarter of the building on the right side still needing to be completed.

The photo below shows the remainder of the east side of the studio with the completed render.

July 03, 2014

The Pour-In-Place Roof

The completed fully water-proofed elastomeric protected earthen roof for the north room after seven coats of elastomeric/rubber/acrylic formulations.  This approach was experimental, but when completed the result exceeded my expectations.  This roof should be extremely durability and easily maintainable.


The photo below shows a close-up of the elastomeric roof after three painted-on coats of AMES Research Maxi-Stretch. The surface looks a little rough, but that's due to the roof's clay/straw material make-up.

Close-up of drain receptacle with final coat of elastomeric (below).

The photo below show the earthen roof after three coats of Ames Research's BlueMAX Liquid Rubber.  The coats of this liquid rubber followed the application of Ames Research Super-Primer.

The first challenge of building a rubberized membrane on top of a clay/straw roof was establishing an initial coat to attempt to adhere to a clay/straw substrate.  This was accomplished with the use of Ames Research's 'Super Primer' which is a penetrating pure acrylic elastomeric plastic sealant.

Earthen (clay/straw) roof ready for the first coat of acrylic elastomeric sealant

The picture below shows the Super Primer acrylic as applied to the clay/straw roof.

A close-up of the dried Super Primer.  You can see the straw that's fixed in the clay and also adhered to the Super Primer.  Despite this whole process being experimental on my part; after this first primer coat, I had confidence the idea of building my own rubber/elastomeric roof from scratch would be a robust waterproofing solution. 

July 02, 2014

Forming the Parapet Wall Top-Cap

After the pour of the concrete top-cap, the inner forms were removed and a final layer of cob (clay/straw) was applied to the earthen roof to establish a contour to ensure rainwater would be directed to the drain.


A hang-over "Lip" was established for the top-cap on the parapet wall during setting-up of the forms by placing strips of 3/4" foam-board on either side of the wall. 

The photo below shows the strips of flexible Masonite board 2" over the top of the parapet wall forming the top-cap.  The Masonite is holding the foam-board in place and itself if fastened by 4"-deck screws that secure into the cob wall - solid.

The photo below shows the completed form all-around including reinforement bar.

Below, a close-up of the south side of the north wall where the thickness has increased to 4" thus transitioning to a bond beam for large main room of the studio.

The south side of the north wall all has metal straps that will be used to secure the vigas (beams) that will eventually support the roof of the main room.

View of the north side wall of the north room.  The use of the Masonite to create curved forms was a real innovation for this curvey structure when pouring bond beams and top-caps.