May 03, 2021

Cobbing: Bond Beam To Roof Line

The next step in the completion steps for the roof over the large room was to build-up the exterior cob wall to the height of the roof line.  As you can see in the first two photos below, the ceiling and sub-roof was built in top of the Ponderosa Pine vigas (beams).  The vigas rest on the concrete bond beam that rings the exterior wall. 

On the left side of both photos you can see the cobbing to the roof line completed from the east wall (1st Photo), working its way along and into the north wall (2nd photo).

The picture below shows a completed section along the east wall about 18" high and between 12" and 20" in width.  This represents a massive about of cob.

The photograph below shows a completed and nicely sculpted north wall section of cob.

The view in the photograph below shows the completed east wall viewing top down.  You can see the rolled-roofing employed to keep the ceiling and sub-roof protected from rain until the final roof structure can be completed.  

This 'final' roof structure will be discussed here in future posts.  The design of which is still being conceptualized, but in general will consist of a cob parapet wall, additional insulation, sculpted light-weight concrete and final rubberized / elastomeric coatings will all be integrated into the solution.

It was estimated that 2-tons of wet cob was hauled up scaffolding to complete the work shown in this post. And as far as the final completion of this large-room roof is concerned, there is still a lot of work to do to complete.  Stay tuned.

July 03, 2020

Spillway For Water Off Dome

Each of the four rooms of this studio have their own custom roof.   One aspect of thinking about what a robust roof system for this structure would look like was thinking how each of the four roof lines would interface with each other - especially in relation to water drainage.  For the 'round room' a dome was built.  I always knew in the back of my mind that I would eventually have to figure-out how to channel water coming-off the dome since to its East was the largest room of the structure that would need a roof of its own.  

Since this studio is being built without plans, my mantra has always been: "I'll figure it out when I get there".  Well I finally 'got-there'.  This blog post is how I addressed the challenge.

Overview: I decided to form a north-south concrete buttress up against the Ponderosa Pine beam (Viga) that was placed at the west end of the large room (see a few posts back for the placing of the roof beams).   I also used concrete to sculpt spillways to direct water in both North and South directions coming off the dome.  The photo above shows arrows generally illustrating the intended water flow direction per my approach.

The photo above provides more detail - almost a 'cut-away' view of sorts to illustrate.  The spillway is below the height of the buttress wall to keep flowing water in the channel.  NOTE: The built-up roof over the large room is not completed.  The entire wall of the structure still needs to be built-up with cob (clay/straw) around the entire room.  

The final wall height will be above the roof line to the top of the parapet.  This work will be done in the fall after the rainy season.  At that time also the roof will need to properly sloped for drainage and waterproofed.  These processes (yet undetermined) will be discussed from this point forward in future posts.

The South buttress and spillway is shown above.  The water drains-off the building.  Since the landscape slopes from North to South, the water draining off here will help water trees in the Mesquite Bosque south of the structure.

Notice the line of tar shown in the photo above.  That is the joint between the built-up roof and the concrete buttress.  That joint needed to be sealed so water would bot be able to enter the living space.  Eventually, a concrete parapet wall will be build on top of this gap and properly sealed to hopefully eliminate that leak potential for the long-term.

June 15, 2020

Building up the Roof Structure

Rome wasn't built in a day and neither is a roof structure.  The last blog post showed the 'barn-board' ceiling installed on top of the vigas, but a ceiling is not a roof.  This post here continues the story. 

One consideration when using the reclaimed barn-board was knot holes and irregular edging which upon installation resulted in minor gaps and see-through holes.  I knew above the barn-board I would be installing a layer of rigid foam insulation and I didn't want to look-up at the ceiling and see the white foam board between any gaps or knot-holes.

My inexpensive solution was to purchase a roll of thick woven burlap fabric and layout on top of the barn-board, secured using a contractor's staple gun (see photo below).


The next layer as mentioned was the application of QTY 8, 4'x 8' sheets of 1-1/2" thick rigid foam insulation.   This R-tech insulation is insect and mold proof (see photo below).  The insulation panels were held in place using wide-head nails.

The final layer for this phase was QTY 8, 4' x 8' sheet of 1/2", plywood.  I need to trim the plywood at the edges where necessary and complete the securing of the plywood with wood screws.

The wall of the structure still needs to be build-up with cob (straw/clay) to roof height and waterproof and drainage.  The summer rain monsoon season is fast approaching, bringing urgency to this phase of the project.

June 10, 2020

Preparing Beam Ends for Moisture and Insects

The ends of the Ponderosa Pine vigas (beams) rest on the concrete bond beam that was poured on top of the cob wall (see earlier posts).  The stray/clay (cob) mix will continue another 12" in height up from the bond beam to the height of the roof deck.

In order to protect thus preserve the beams for the life of the building, the beams need to be protected from moisture and wood boring insects.  An inexpensive method to protect the ends of the beams is to use 'asphalt emulsion'.  Asphalt emulsion is essentially a petroleum-based tar with a consistency of a thick paint.   This product can be purchased at a building or masonry supply store.

The photos here show the coating applied. I used a paint brush to apply and the emulsion  dried fairly rapidly.  


Notice the large-head nails extending at the ends of each viga.  The purpose if to help secure the cob against the beam when the cob is applied onto the top of the bond beam. 

The construction of the roof system above the large room is far from over.  More posts to follow.

May 30, 2020

Large Room Ceiling

I didn't decide ahead of time on the look of the ceiling for the large room.  Like most of the decisions during the construction of the 'Studio', I figured it out when I got there.  

When I did 'get there', I came across what I thought would be a good aesthetic material at a reasonable cost - Barn board.

Originally, I had considered small (2"-dia) pine poles for the latilla's on top of the beams, but I couldn't justify the premium expense for the poles and was willing to see what other options would eventually make themselves known.

A few weeks back during my search for vigas I came across a reclaimed lumber company in Mesa, Arizona - "Old Sol Lumber Company".  They suggested barn board obtained from old barns as dismantled in Kansas.  Looking at their stock, I really liked the texture of the old wood and the fact it had a history. 

From a practical standpoint, I knew I could obtain the needed 300 sq.ft. from this supplier in one shot and thus would save time.

Before I picked the barn-board solution my wife had suggested making the ceiling of old doors.  I really thought that it was a good idea, but finding suitable doors would be a more involved search for the style and quantity needed for the ceiling.  Another consideration was time because I'm trying to get most of the roof system in place before the monsoon season that begins here in southern Arizona around early July.  Note that the final roof structure probably won't get completed until after the monsoon season in the fall.

Ultimately the choice of Ponderosa Pine vigas along with the barn-board ceiling will present an appropriate and aesthetically suitable compliment to the studio's overall design. The vigas provide an historical building context - traceable to Anasazi construction methods (see below).  The reclaimed barn board will have the effect of being brought-back in time.


The photo below was taken at the magnificently constructed Anasazi structures in Chaco Canyon (NW New Mexico) built around 1100 AD.  The Anasazi used pine vigas hauled from the forests by hand 20+ miles from Chaco.  This is the Studio's connection to ancient architecture of the Americas.

NOTE: This posting is just the start of the large room roof's structure.  I will update this blog to detail each step of the roof's construction.

May 07, 2020

Ponderosa Pine Vigas for Large Room

For the large room, six Ponderosa Pine vigas were utilized for the main roof support.  The room shape is an irregular oval roughly 15-feet by 17-feet.  The vigas were 10"-dia and rest on top of the concrete bond beam (see previous posts).  The building code requires that the beams rest (overlap) the bond beam 12" on each end.  The beams were spaced approximately 30" apart on center.


The vigas were purchased at Southwest Ideas in Surprise, Arizona.  They were hard to find.  There are very few forest product companies left in Arizona.  Not sure why - with all the Southwest designed buildings in the state one would expect a healthy market for vigas, thus several suppliers. 

I rented a 24-ft 'Stake Truck' from Ryder Truck Rental to transport the vigas from Phoenix.  The length of the beams were 17-feet.

I hired a local contractor with a boom truck to assist in hoisting the vigas to the roof, where myself and a laborer set the beams at the locations and spacing I marked along the bond beam.

Below is a roof view of the vigas laid in place (below).  Notice the metal 'Strong-Tie' straps holding the vigas in place.  The metal securing straps were embedded in the concrete of the bond-beam as mentioned in the previous blog that discusses the pouring of the bond-beam.

This post will be the first of several that will discuss the construction of the roof structure.  The laying of these beams required the most coordination between the supplier, transportation and on-site equipment and personnel to install.  The rest of the roof construction will be mostly a labor effort.

May 03, 2020

Some Exterior Finishing Work

In my last post I covered the concrete bond beam that will support the beams and roof structure for the large room.  

In this post I want to show how I finished a section of wall along the south side of the studio that is common with the large room and a smaller room that extends out to the south. 

In the photograph below, the foreground is the roof of the smaller south room.  The 'cob' wall that is common with both rooms is capped by the bond beam that will support the aforementioned large room roof.

What I needed to figure-out was how to seal the exterior cob wall so rain would not deteriorate the wall and allow rain to infiltrate and undermine the rolled-roofing that extended up the wall creating a parapet (a 'flashing-type' solution).

The obvious solution for an exterior adobe wall would be traditional lime plaster.  However, for this small section and knowing from experience that south-facing abode walls with lime plaster need periodic maintenance due to thermal-expansion.  The daily hot-cold cycle of the desert here in Arivaca ranges  between 40-45 degrees F.; thus this expansion and contraction eventually results in the lime plaster separating from the adobe wall.  

There are mitigation solutions such as roof overhangs and ''chicken-wiring" the wall prior to plastering, but that's not how I wanted to approach this small section.


When pouring the bond beam I provided for a 2"overhang over the exterior of the cob wall.

In the photo below I used 1/4" cement board secured to the cob wall with 4" deck screws and large washers.  The cement board acted as 'flashing' as it is under the lip of the bond beam and then extends down over the top of the rolled-roofing so that it will shed water onto the roof below.  The cement board also acts as a substrate from which the applied cement mortar provides for a more robust finish.

I applied this same finish method to another part of the structure - again, in another small section where i was looking for a more 'maintenance-free' solution.  This time however, I added tiles made by a local potter to add an artistic touch (photo below).


April 18, 2020

Bond Beam Completed for Large Room Roof

There is one more roof to put on the studio. Three of the four roof lines (one of which is the 'dome') have been previously completed.  I needed to complete the bond beam for this room, before the roof work can begin.  The bond beam supports and distributes the roof beam load and ties the wall together with the roof structure.

STEP 1: Gathering Materials

Concrete is a mixture of Portland Cement, sand, gravel and water.  I have a dry-wash on my property so I am able to provide for my own sand right on site.  I sifted the sand with a fine screen into a wheel barrow and piled by the mixer.   

The gravel was obtained from another dry-wash in the nearby mountains (see back of truck in photograph).  Gravel size ranged from about 1-1/2" down to pea-size. 

STEP 2: Construct Bond Beam Forms

The bond beam sits on top of the the adobe wall.  I call it a "footing in the sky".  Due to the curved nature of my walls, I couldn't just use masonry 'bond-beam' block [which is similar to a common cinder-block but rather has a "U-shaped" channel on top where you can lay-in rebar, then fill the hollow block with concrete - stacked side-by-side to form monolithic beam].

So I came up with the idea to purchases several sheets of 'Masonite board' to create the form which is flexible and would conform with the curved-shape of the wall.  The Masonite was cut into 16"-wide strips for this purpose.

Notice in the right-side of the photograph (above) that I was able to build-up the cob (clay-straw) wall to act as a form on one side.  The wall is about 18"-thick at this location, so 12"-wide of that will be the concrete bond beam.  Thus from the outside of the building, you will only see the cob wall (about 6-inches of thickness of cob).

Bond Beam Form Details

The photograph above is a section detail of how the bond-beam form was fabricated  For this part of the wall there was the masonite form on each side. Notice the short vertical wood stakes I used to support the form. The stakes are fixed to the wall by 4"-5" deck screws.  What was an amazing discovery about cob is that you can screw into it and it holds firm!  

There is two rows of 1/2"-dia rebar laid horizontally, wire-wrapped to vertical rebar that extended-up through the wall.  This locks the bond beam to the wall.  The dimensions of the bond beam are roughly 12"-wide by 5"-high.  The section of bond beam poured for this project was 35-feet in length.

Notice the metal 'straps' in the picture.  They have a hole toward the end so the rebar can go through to secure the strap embedded in the concrete.  The metal strap will extend-out about 2-feet from the top of the bond beam and will eventually secure the roof beams.   Thus that completes the securing of the roof to the bond beam which is secured to the wall.

One further thing to note. Notice in the bottom-foreground of the photo you can see white foam.  I placed the foam there to act as a spacer to extend the bond beam width out over the top of the wall to create a "lip". That is because this portion of the wall separates two rooms with the room in the foreground (white top of roof in photo foreground), from the higher large room roof.  So the 'lip' on the outside will allow eventual flashing to protect the weather-side exposed wall from underneath the lip down to the top of the lower roof of that room. 



A standard concrete mix for structural applications is roughly 1-part Portand Cement, 2-parts sand and 3-parts gravel, with about 1/2-bucket of water (see photo above).  However, after the first mixer load, I observed the mix to be too 'rocky' and didn't produce a smooth 'workable' surface. I realized the sand I was getting from my wash was more like tiny gravel than fine sand.  Therefore I changed the mix to 3-parts sand, reducing the gravel down to 2-parts from 3-parts.  That worked better.


I hired a helper to assist with the pour.  I mixed the concrete in a mixer than used 5-gallon buckets to haul the concrete up the scaffolding to the worker on top who would empty the bucket into the form and ensure the concrete was uniformly spread and leveled on top.   I only filled each bucket 1/3-full due to the weight of hand-carrying up scaffolding. The whole process took 3-1/2 hours to pour 35-feet of wall with a mixer and the two of us.  I used five 47-lb bags of Portland Cement and associated aggregate as discussed to  complete the bond beam  I calculated using an online concrete calculator, that 35' x 1' x 0.5' of form equals about 0.65 yards of concrete.

The photo above shows what a portion of the bond beam looks like once the form is removed. Now you can see the metal straps ready to secure the wood support beams which will be the next step.  Also, this the portion of the bond beam where I talked about the 'lip' extending over an existing roof in preparation for a flashing solution.

Note that the Masonite, screws, washers, and wood support stakes are all saved for future use.

June 18, 2019

Scaffolding assists work efficiency & safety

The photos below show the elaborate extent of scaffolding set-up to assist in the efficiency working on wall that approach 12-feet in height.  Instead of having just one of two scaffolds that have to constantly be moved around, the investment I made in multiple scaffolds set-ups, allows for just focusing on applying cob to the walls without interruption as work progresses along the structure.

In addition, the 3-foot wide platforms provide a safe and stable working environment at such height.

East side of structure (looking west)

Inside the large room awaiting a roof - More scaffolding on the inside.

South wall of large room

East wall finished to bond-beam height

The primary "cobbing" of the studio structure is now finished with the completion of the east wall to final height (see photo below). The next step will be to set forms on top of the wall in preparation for pouring the concrete bond beam.  

In the back-ground of the photo you can see the bond-beam that was completed along the north wall that will now be extended around to the east and south walls.  Once the bond-beam is poured, construction of the roof for the main room can commence. 

May 28, 2019

East Room Wall - Cobbing Toward Final Height

With approximately 1-month to the start of the summer monsoon season, it looks like the east room will have to go without a roof, but cobbing continues to build the last part of the east wall up to final height.

The photograph below shows a section of the east room wall with the cob level at the wall's final height. The North section of the wall already has had the bond beam poured.  Once a form is constructed on this newly completed section of the wall, concrete will be poured about 4-5" thick to establish the bond beam.  This will be documented when the time comes so keep checking this blog over the next few months for updates.

The left side of the photograph above is the completed (level) east wall at final height.  The right side of the picture shows what is left to cob.  The vertical rebar extending from the top of the wall, represents the surveyed final height.  A surveyor's level was used to accomplish the task of measurement. 

February 23, 2019

No Progress Update, But Here's a Short Film

Its been since June of 2018 since I have worked on the structure.  A lot of competing priorities kept me focused on other things.  Work will resume in March 2019 with the focus on completing the wall on the main room in preparation for the bond beam, followed by a roof structure (design of which is still undetermined).

In the meantime, here is a short experimental  doc-u-film by Tucson film-maker Adam Ray and myself titled "The Dome".  The film won the "Best of Arizona" award at the 2018 Arizona International Film Festival in Tucson, Arizona.

Link to film on VIMEO:

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: 

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 ( ); 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).