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Adobe Joe

12 Apr

Joe Tibbets sharing his knowledge

Joe Tibbets of Southwest Solar Adobe School is now online with a blog, Adobe Joe, and Facebook page, Adobebuilder.  Long-time adobero and instructor, Joe is a wealth of knowledge about adobe and solar construction. Ed and I participated in one of his 2011 workshops (link to video), and we continuously incorporate his information, techniques and advice during our projects. Joe’s humor and stories enriched the experience, and we hope to visit with him again in the future.

I highly recommend his workshops to learn the art of using adobe, constructing hornos, designing with and implementing solar energy principles. Visit the website for the Southwest Solar Adobe School, Adobebuilder, to learn more about adobe and workshops offered near Belen and Albuquerque, New Mexico.

Hope to see you this fall, Joe!

Adobe wall creeps along with a lizard

12 Apr

Adobe wall slowly grows taller

Work on our place has stalled due to construction jobs elsewhere in the desert. We stole one day to lay a few courses of adobe block on the arch, but have several more courses to go before the ramada west wall is done.And we continue to experiment with plasters, as you can see on the adobe wall. They will eventually be chipped off before the ‘real’ plaster is applied.

First cob sculpture: lizard!

With a few hours to spare at the end of one day, and with a bucket of heavenly red clay sitting there shouting at me every time I pass it, I mixed up some of that clay, black volcanic sand, and a couple handfuls of chopped dried grass that we harvested from alongside Terlingua Creek. Bit by bit I added water, played with the cob, and a lizard started talking to me. And now I have a dark reddish brown lizard buddy that is still solid despite drying in the sun for nearly a month. I think he is deserving of a red clay slip to hide the grass clippings and look more elegant. Then I’ll have to find a place to incorporate a vertical block!


A new addition to the El Punto family: a 2,700-gallon capacity tank. We’re very happy!

Happy water cistern.




First Adobe Production Run

5 Mar

Two clay and sand sources and mixer.

Based on our first experiment making adobe blocks with the new cement mixer, we did our first production run with the mixer. We prepared for this run by building two ladder forms: one continuous form for four 10”x14”x3” blocks with handles at each end.  On tarps next to the mixer were piles of screened dirt from two different sources: Black Creek Draw (BCD) and South County (SC). (We have so many dirt samples now that we are assigning codes for each sample.)  A five-gallon bucket held the remnants of Portland cement (PC) from an older bag. Another bucket held water, while the 80 oz. bucket was used for measuring the water during mixing.

We delegated jobs between us for efficiency and consistency: Ed would mix, I would wheelbarrow mixed mud to the casting site, clean and pack forms. This allowed Ed to mix batches while I packed mud from the previous batch into forms and cleaned the second form for the next batch.

The previous day, Ed had made test blocks from each of the two dirt sources without cement (unstabilized blocks). He also made a test block from a 50/50 ratio of the two sources. This helped to determine the optimal ratio of the two for the final run. It also later proved to be invaluable for troubleshooting. Like any scientific approach, controls (negative and/or positive) are necessary for accurate comparative analysis and interpretation. Weeks afterward we agreed to institute this as standard procedure for future earthen experiments.

Sedimentation (jar) test of soils.

Jar Tests. In addition to the test blocks, we also did a jar test of each dirt source. We filled each jar to the 400 ml graduation with dirt and added ~400-500 ml of water with a small drop of dish soap. After vigorous shaking for at minimum of 60 seconds, the jars were allowed to stand for at least 4-8 hours before evaluation. In the photograph, the open jar contains BCD dirt; the closed jar, SC dirt. Other than different colors of the sand, both have almost equivalent amounts of clay/silt fraction.  Both jars did not have clear delineations between fractions of silt and clay, but we decided to go ahead and do a 50/50 ratio of the two sources for our final run.

Test blocks of SC & BCD dirt.

Test Blocks.  Test blocks appear in the annotated photos. The two blocks in top row, right to left: cured 100% SC block, cured SC + 2 handfuls of clay + PC. Added cement imparts a lighter cast to earthen blocks. Bottom row: 50/50 SC + BCD block (green) and a half-block made from residual mud from BCD (top ¼) and the 50/50 mix (lower ¼). The single block: 100% BCD (green).

BCD dirt test block.

In mixing the first batch, Ed added all the water at once to the dry components.  We decided to gradually add buckets of water in subsequent batches because both dry and liquids mixed more consistently.

The first two batches of mud were too dry, and pressing mud into the form edges and corners took too much time. Also, gaps in the mud along the edges could be seen when the ladder form was pulled off the first batch of blocks, further confirming the mix was not wet enough. Ed increased the water content (ratio) in subsequent batches, which resulted in a wetter slump that was quicker and easier to press into the forms and no gaps in the formed blocks.

Because some residual mixed mud was always left in the mixer and in the wheelbarrow, Ed reduced the volume of dry components after the first batch. Mud remaining in the wheelbarrow (from ½ to 1 shovelful) was shoveled into the mixer near the end of the mixing time to be incorporated into that batch of mud. The mixing time was also increased from 10 minutes to 15-20 minutes.

Batch mix ratios:


Batch 1 #shovelfuls

Batches 2-11 #shovelfuls

SC 10 9
BCD 10 9
PC 2 ¾ 2
Water 5 5
Mixing time 10 min. 15-20 min.

General procedure:

  • Shovel dry ingredients into drum, alternating 4-5 shovelfuls/dirt source, and finally adding the PC. Let dry components mix for a few minutes.
  • Add water gradually, bucket by bucket. Allow to mix for ~30+ seconds between buckets of water.
  • Mix all components for ~15-20 minutes.
  • Meantime, mud from previous batch is being shoveled into one ladder form with one person pressing mud into bottom, edges and corners making sure that blocks are leveled with top of form. Tops of mud are patted as level as possible. Be sure to lightly wet hands before pressing mud; otherwise, mud sticks to hands and can even lift chunks of mud out of form.
  • While all components are mixing, two people lift form off blocks from pervious run. Person mixing then takes wheelbarrow to mixer to combine residue in drum and place wheelbarrow under the mixer for emptying. Form person cleans the empty form, wiping interior sides and corners with water. Important to have interior of forms moist; otherwise, mud will stick to wood and form will not slide off with ease.
  • Form person wheels the new mud to the prepped form and begins to fill and pack.

Because we had unexpected visitors (locals), we didn’t start our run until 2 pm. Our first 2-3 batches were working out some details on the mix components and the general routine. Once we established the right mix and routine, the entire production run went quicker and smoother. We ran out of cement at batch 11 and at 44 blocks around 5 pm and called it quits there. We were also running out of casting area on the ground. With only enough dirt for another batch, we agreed it was a productive day: 44 blocks (11 mixer batches) in three hours, and a little over a half-hour for clean up.

Casting area and new blocks.

We learned a few lessons from this first production run:

  1. Have three ladder forms available. Pulling the forms from newly cast blocks after only 10-15 minutes was almost too soon with this moist mud. Ideally, we should have given the blocks another 15+ minutes to set before pulling forms.
  2. Place ladder forms on level ground. And don’t try to prevent mud from flowing outside of the form bottoms. I was ‘damming’ some of the open edges and corners inside the forms with loose sand. We discovered half-way through the run that this prevents the mixed mud from being pressed tightly into the corners and leaves large gaps in the blocks after the form is pulled.
  3. Casting area really needs landscape cloth for making adobe blocks. For two reasons: to prevent issues outlined in #2, and to prevent the wet adobe mud from binding with the dirt and sand underneath. We realized this was a problem a few days later when the new blocks were stood on their edges. It became more apparent and detrimental later when we worked these cured blocks with extremely uneven bottoms into the adobe arch of the ramada.
  4. Always, ALWAYS, use fresh Portland cement if you are making stabilized or semi-stabilized blocks. We discovered two weeks later that edges of the cured blocks spalled more than we expected. The edges crumbled with pressure; more than we liked and wanted in our blocks, but not enough to seriously compromise their strength or integrity. Regardless, they did not fully meet our expectations, and we were stumped as to the cause of this spalling.
  5. Always (there it is again) make an unstabilized test block of any candidate soil to be used for adobe blocks. Like a control, these test blocks may prove to be invaluable for later comparisons. Soon after casting in a form, inscribe a code assigned to that soil mix or component into the face of the still-wet block for later identification.

We were quite excited about this first production run until we started using the blocks in the wall of the ramada and discovered that the edges crumbled more than we prefer. My suspicions were that the silt content in either soil was high, or that the bentonite clay content in the BCD dirt was high. For comparison analyses, we went back to the test blocks with and without the Portland cement that we used in our production run.


To our amazement, the unstabilized blocks made from 100% SC dirt, the 100% BCD block, and the 50/50 SC+BCD were as hard, or even harder than cinder blocks! No spalling and the edges were hard enough that they resisted any crumbling and spalling. Then we examined the semi-stabilized SC text block (with cement). The sharp edges of that block crumbled with hard pressure from my fingers and Ed commented that it was much whiter than usual for a semi-stabilized block (which can be seen in the photo of test blocks).

My first suspect was too much bentonite clay in the Black Creek Draw dirt. Cement mixed with dirt high in expansive clays, such as bentonite, is relatively ineffective because the two components tend to oppose each other and result in low bonding strength. When rolling some of the BCD dirt into a ball in my hand, it felt more slimy than the SC dirt. Thus, the BCD may have some bentonite clay in it, but the 100% BCD block (with no PC) had solid and hard edges, resisting finger pressure and crumbling.

Another suspect was silt content, which remains an unknown in both sources. In both sedimentation tests (aka, the jar tests) for the two dirt samples observable strata of silt did not show. Possibly because most of the silt was still mixed in with the sand strata. However, if high silt contents were the cause of spalling, then it would also be seen in the unstabilized test blocks. And it was not.

While discussing these issues, Ed remembered that the bucket of leftover Portland cement he used in that run had clumps near the bottom, indicating that it had absorbed moisture over time. Cement and lime are both hydrophilic, which means they attract and absorb moisture, even from the air.  Both cement and lime require water for their chemical reactivity. Once moistened and reactive, quick (hydrated) lime and cement begin to bind with the mineral components in the mud. As the block cures over time, they become stronger and dense while at the same time, their binding reactivity decreases.

Accordingly, if a bag of lime or cement is exposed to humidity or water in the air, it will absorb moisture and begin to ‘set’, or react with itself. Lime especially is highly reactive even to the carbon dioxide in the air. If not tightly bagged, it can absorb both moisture and CO2 and become ‘stale’. If too stale, the reactivity of lime can be severely impaired for any future use as a building material additive. I have had a bag of Portland cement harden like a rock while still in its bag in my barn near Fort Worth. Several observations here strongly suggest that the culprit was the old ‘stale’ Portland cement. Hence, Lesson #4.

First Adobe Arch

Between previous blocks made with clay and sand from Cedar Springs (CS) and the 44 blocks recently made, we had enough to start constructing the adobe block arch in the ramada’s west wall. That, too, was a learning process as it was our first arch. We are short about six blocks to finish the entire wall and will be doing another adobe block run soon to make up the deficit and have blocks for another project.

By mid-March the west wall of the ramada should be completed. And then we can move on to begin the next major project: the foundation for the earthbag guest house!

Adobe arch of ramada and experimental plaster wall.


Solar overhang calculator: Shade your windows!

6 Feb

An important component of passive solar design is calculating building openings (doors and windows) and roof overhangs. For instance, several features of a window will influence gain of solar heat and shade. The size of the window -width and height- and the window’s relationship to the roof -the space above the window- influences the direct and indirect gain of solar heat. For example, if the roof’s overhang does not shade the window during the hottest hours of the day, direct and reflected sun light will heat the interior. That might be desirable during winter months, but very uncomfortable during hot summer months.

A designer can draft the angles of the sun or refer to charts to determine heat gain and shading with laborious drawings. On the other hand, one can use interactive tools on the Internet to aid  decisions in placing windows to avoid heat gain in summer and maximize solar gain in winter. Additionally, this is an excellent tool to design a Trombe wall in a south wall for maximal heat gain and storage in an earthen wall!

An innovative and helpful solar tool is an Overhang Annual Analysis (the beta release of new version) on the website, Sustainable by Design. Developed and maintained by Christopher Gronbeck in Seattle, WA, two versions of the tool can be used. The beta release includes advanced features, such as accounting for diffuse and reflected light. What’s the difference, and does it matter? Wait and see.

In the examples below using the advanced beta version, I entered the latitude of Terlingua, TX, and basic data about one window, it’s location (e.g. south wall) and the overhang. Additional input includes sun mode (direct sun versus direct + diffuse + reflected) and overhang width. Since the eaves of our roof will overhang the entire wall, I did not change the default (‘wider than window’). For the first example, I chose direct + diffuse + reflected sun mode (in oval) and entered the dimensions in the appropriate field in the captured image below.

Percentage of shade for window with overhang; direct, diffused and reflected sun.

Now, compare the calculated data in the image above with that below after calculating for direct sun only (again, see field in oval).

Solar gain/shade calculated with direct sun only.

The first calculation is probably more representative of the true value of net solar gain, or total solar radiation on the window, depending on several factors. It includes direct sunlight, diffuse light from the sky, and ground-reflected radiation. If the window is close enough to the ground to catch reflected light on a cloudless sky, total radiation will increase that value (compare to same time/month in second example). This source of radiation should be factored into placing and sizing windows in a wall.

Also, if shutters are placed on the exterior of the window and opened and closed during hours of the day when solar gain is high, this will future reduce or increase total solar radiation. Another design feature to consider to windows in the overall structure.

Now I want to determine the solar gain for a 5′ tall Trombe in the south wall. A Trombe wall is a space incorporated into the wall with fixed glass exposed to the exterior. Some type of thermal mass behind the air space and glass captures and stores the heat from the solar gain, which diffuses into the interior during cooler hours of the day (diurnal flywheel). Our thermal mass will be adobe blocks or narrow earthbags. Also, similar to our windows, our Trombe walls will have shutters that will help reduce total solar radiation gain when needed.

Calculated for 5-foot south-facing Trombe wall.

Trombe wall.

The photo on the left shows an adobe Trombe wall in a building under construction by Joe Tibbets at the Southwest Solar Adobe School (Belen, New Mexico). The adobe blocks in the Trombe have a dark clay slip on them. It is positioned between twin sets of windows and as yet does not have the exterior glass installed. A dark surface inside the Trombe will aid in absorbing solar gain and heat.

As you can see, these online calculators can really help in design decisions!

Adobe Test Blocks Again

26 Jan

“A cement mixer is your friend.” We’ve heard this many times from people making their own adobe blocks and concrete for various projects. After mixing components in a wheelbarrow three times in a day, I was lusting after a mixer.

Ed adding components to the mixer.

We finally bought a new 4 cubic foot mixer that was priced as a special from Northern Tool Company during a trip for a family event in Fort Worth. Like most any consumable product these days, it came in a box. We wondered how a good sized cement mixer could fit in a box, but it did. (I questioned if products are now standardized to fit in boxes.)

As Ed expected, the instructions for putting the mixer together were more than inadequate (pidgin Chinese?); some segments were wrong. Because of Ed’s mechanical background and experience with poorly written manuals, he had little problem putting it together. From my experience editing science and technical manuscripts written by non-English authors, I could only imagine. Regardless, it was soon put together all burgundy and shiny, waiting with gaping mouth and hungry for hard stuff; “Feed me!”

One sunny and warm day this week, we decided to try our hand at making adobe blocks with our newest member: Audrey.  (Classic musical cue here) Ed had several five-gallon buckets of adobe mix components waiting next to the front of the mixer:

  • Clay: sourced from a hillside near Cedar Springs area and which has proven to be good clay for adobe blocks (see former post),
  • Sand: crushed and screened recycled adobe blocks that were rejects because they were too high in sand (they broke apart VERY easily)
  • Cement: regular Portland cement
  • Water from our rainwater catchment tanks
  • We have at this time forms for only four blocks.

We began by screening the clay on a 3/8-inch screen over the wheelbarrow. Very little aggregate was discarded after using gloved hands to break up clumps on the screen.  About ¾ of a large bucket of raw clay (before screening) was enough for each batch.

We made two test batches. The amount for each test batch was as follows:

  • Clay: 5 shovelfuls
  • Sand mix: 15 shovelfuls
  • Cement: 2 shovelfuls
  • Water: 5.5 buckets (bucket holds 80 oz.., ergo 3.4 gallons)

Mixing time was a new variable that we also wanted to test based on comments in Gernot Minke’s book (Building with Earth: Design and Technology of a Sustainable Architecture, 2nd edition, pub. 2006). Regarding clay, mixing time was an important influence on mixtures for plaster and blocks/bricks that contained clay. According to tests at the university lab in Germany, extending the mixing time from one to ten minutes enhanced bonding capacity of the clay and water adsorbance in the mixture (1). On the other hand, extending duration to 20 minutes reduced the bonding capacity. We tried two durations: Batch 1, 7-10 min. Batch 2, ~15 min.

Batch 1

Number of blocks: 3 whole blocks + ~1/2 of a block left in the wheelbarrow.


  1. Ed started mixing the second batch while I filled the block forms with mix from the first batch.
  2. This mix had a nice slump, probably between the consistency of grout and mortar (2). The consistency was similar to the mixes for blocks made at New Mexico Earth near Albuquerque; loose, but not watery. It is fluid enough to easily fill the form corners without a lot of hand-forming, but not too wet that the blocks crack easily.
  3. As with both batches, Ed added all the dry ingredients first, then added water. With the first batch, he added the water a bucket at a time with ~30 sec of mixing in between, then adding another ½ bucket after mixing for a minute or two.
  4. Because there was not enough mixture for another whole block, I left the remainder in the wheelbarrow to mix with the second batch. It is important to shade the leftovers from the sun to prevent drying too quickly.
  5. Forms were pulled while second batch was mixing. (~12-15 min).

Batch 2

Number of blocks: 4 whole and 2/3 of a block


  1. This mix was noticeably drier and grainier than Batch 1. Although the water content added was the same, the difference may have been larger shovelfuls of the sand or clay. Ed discovered that constancy between shovelfuls was difficult to maintain because of trying to scoop components from a bucket
  2. This batch, Ed added all the water in quick succession and then let mix for extended time (~15 min).
  3. Related to #1, the slump of this batch was stiffer and required a lot more time from both of us to push mud into the corners, lightly compress with our hand and also screed the top with our hand. This is a good reason for a looser slump of mud!
  4. More blocks were made from this batch because of the residue left in the mixer from Batch 1 and the unformed mix in the wheelbarrow, also from Batch 1.
  5. Because of the drier consistency (slump), Ed pulled off a form from one of the blocks to fill in with the left-over mix to make the 2/3 block.

Overall, from beginning the first batch to clean-up (tools, mixer, wheelbarrow, hands) was ~ 2 hours.

‘Green’ adobe blocks. Top, Batch 1. Bottom four+, Batch 2.


  1. Set-up and clean-up times are time intensive. Ideally, we would like to have a larger volume of materials in big piles on tarps. We ran out of our sand component (the crushed recycled blocks).
  2. This would also facilitate longer production runs (4-6 batches) and consistency in shovelfuls as measurement of mix components.
  3. For clean up, a large shallow pan or stock tank ½ full of water would facilitate efficiency of water and cleaning tools. It would also facilitate wetting the inside surface of the block forms to avoid the mud sticking to the forms.
  4. More materials. Can’t be said enough.
  5. If we can make 4-5 blocks/batch, than we will probably make ladder forms for that many blocks. I also want to get some landscape cloth to put on the ground underneath the forms.
  6. We still need to experiment with adding the water. The second batch had some dry clumps in the bottom of the mixer. Add water a bit at a time, like we did in Batch 1? Or all at once, as in Batch 2? I think this still needs experimentation.

A note on the recycled blocks. These were reject blocks from a project north of us. They break and crumble easily and spall (particles fall off the block when lightly rubbed with the fingers, or as they erode from weather). Consequently, they have very poor tensile and compression strength. We also discovered that plasters do not adhere to these blocks because the granules are so loose (spalling).

Another contribution to their loss of integrity is that they were stored outside, stacked flat on pallets, and with pallets on top of pallets. Most of these blocks that we picked up are being recycled. Those that are stronger are being used in the west wall of the ramada. However, new blocks that we are making and that pass our strength and compression tests will be used for the arched window in that wall.


    1. Clays are like ‘chemical sponges.’ Clay minerals are colloids with large flat surface areas and carry negative or positive charges on their external and internal surfaces. Thus they have the ability to attract other charged particles, especially many water molecules. Because this attraction is a surface phenomenon, it is called adsorption (which is different from absorption because the ions and water are not attracted deep inside the clay grains).
    2. Slump is commonly the consistency of masonry materials in a specific batch. The fluidity and plasticity of material varies for different applications, such as concrete, mortar and grout. For discussions on slump, visit these two websites: What Is Grout and Slump Testing.

The adobe west wall of the ramada. It’s also our plaster test wall.


Hassan Fathy’s New Gourna (video)

26 Jan

Hassan Fathy’s New Gourna

“The village of New Gourna was designed and built in the 1940s by the Egyptian Architect Hassan Fathy. He pioneered the use of sustainable materials and environmentally friendly design to build housing for low income families who were being relocated from their original village at Old Gourna. 60 years later, many of the now historic New Gourna buildings have fallen into disrepair and others have disappeared or been changed beyond recognition.”

A beautiful and powerful video by Oliver Wilkens on the sense of and attachment to place.  I find it interesting that these earthen structures built in the 1940’s along the west bank of the Nile River are disintegrating (40% of the original buildings are gone), especially at the foundations. Comparing this to adobe and other earthen structures in this country that remain standing 100 years or more, I wondered what contributed to their destruction. Without knowing details of the environment, I cannot say for sure. However, some clues can be found in the video.

Several points can be raised:

1. A building, made from any material, is only as good as its feet and hat, aka foundation and roof. Two comments from the video raise concerns. One is the presence of a shallow water table, which should be factored strongly into the foundation construction. The other is comment regarding roof collapse.

2. Know your materials. Several references in the movie to the foundation stone being made of ‘salt’ suggest that despite plentiful access to local rock, perhaps the type of rock was not the best choice as foundation material. One of the men in the video comments that if sandstone had been used for the foundations, they would not have degraded as quickly. Match the construction materials with the environment.

3. Fathy is known world-wide for his application of incorporating local resources and sustainability concepts with vernacular architecture. However, premature degradation of the New Gourda earthen structures underlines the importance of integrating modern, innovative technologies with traditional and culturally-sensitive materials.  Additionally, residents need to learn and acquire the skills to meet the needs of community while preserving the past, including repair and renovation of their structures. This is especially true in light of changing environmental and economic conditions.

4. A home, any shelter, is an ongoing interactive process, especially when constructed of earthen components. When visiting most of the pueblos in the southwestern US, it is common to see people administering to their homes and buildings, such as plastering or other maintenance. Anyone with a conventional home constructed of wood will know that as the structure ages, repairs and maintenance are required. Several comments in the video attest that frequent and ongoing maintenance and repairs are required for these buildings. In this case, both the local people and the UNESCO World Heritage Center are re-evaluating the existing conditions, design and materials to rebuild and/or repair the structures.

This is an engaging and powerful video to watch.

Adobe is my birthstone

3 Jan

“The adobe is my birthstone.
What else could it have been in the little mud-brick pueblo of Los Angeles onthe day of my birth….The adobe? Perhaps gringos would question why I speak of it as a birthstone at all. They might say it is just a dirt block.

To me, the adobe is more than that. It is the good earth upon which the
questing steps of men and women have trod for so many centuries seeking
something fine from life. With this good earth is mixed the water upon which
all mankind has depended for existence since life was created. And upon this
earth and water the sun has cast its radiant beams to unite the mixture so that
the resultant adobe is the happy fusion of nature’s finest elements.

Even the making of the adobes is a symbolic act. The water and earth are
mixed under the bare feet of man himself. Man treads with vigor and purpose
upon the adobe to which straw is added for strength. Man, who always is noblest
when he works, thus furnishes his labor to what God has given him, and from the
honest toil the adobe emerges ready to be placed in large forms for drying in
the sun.

When they are baked by nature’s own heat they are used for the building
of homes. We are surrounded then in our dwellings by the elements of earth and
water fused by the divine actinic rays of the sun. The adobe bricks become the
witnesses of our lives. These adobe walls mellow with age. They share in the
love of our young people, the birth of our children, the death of our old.
They enclose us comfortingly. They are our shelter from cold and heat. They
enfold us like a mother’s arms.

Of course, it might be said that more elegant birthstones could be chosen.
The scintillating diamond is credited with indications of wealth and power. The
star sapphire is linked with good fortune and even with the Star of Bethlehem.
The ruby is associated with strange deeds and spells cast upon those born within
its sphere.

Yet the adobe possesses qualities which none of these can match.
Pais, agua, sol.
Earth, water, sun…

Pais means more than soil or earth, far more than the Spanish word “tierra,”
which is merely mundane. It means something spiritual; that as a man’s feet
touch his native ground there is a mystic bond between him and the dust from
which he was molded….”

from The California I Love, by Leo Carrillo

For Love of Mud

14 Dec

A video of Verena Maeder (Solid Earth Adobe Building, New Zealand) from .

What’s in a block?

13 Dec


While Ed spent two days working on a door jamb at Cedar Springs Ranch (Terlingua), I experimented (like the good scientist that I am) with making my first adobe blocks: solo. All the necessary supplies from El Punto were loaded into the truck to take with us: wheelbarrow, new mortar hoe (like a garden hoe, but with holes in the blade), two block forms (a double and single), a bucket of lime, gloves, mask, and two empty buckets. The other constituents – sand, clay and water – were yet to be gathered. And I had a source in mind: my favorite black arroyo bottom.

Dark sand in arroyo bottom.

An arroyo runs through Cedar Springs Ranch carrying tons of black volcanic particles: sand.  After a rain it all glistens like a black milkyway poured from an invisible bowl. The black or dark gray contrasts nicely with the rest of the desert floor which is dull white to light beige, and provides a wonderful contrasting backdrop to wildflowers blooming in or next it. I’ve always wondered what adobe blocks would look like made from this sand and this was an opportunity to find out.

Know Your Mud

I disregarded the general rule of thumb when evaluating any potential source for making adobe blocks. Know the ratios of sand, clay, and silt in your native soil. The best evaluative technique is to do a water and jar test, or soil hydrometer test. Fill 1/3 of a quart glass jar with the mixture (sifted and free from rock) and bring up to 2/3 volume with water, leaving about an inch of air space at the top. Add a drop of detergent, which acts as a surfactant and helps separate particles. Cover and thoroughly shake for several minutes. Let sit undisturbed for at least 24 hours to allow the contents  to settle into layers (sedimentation).

Sand settles at the bottom within a matter of minutes. Silt settles on top of sand within three to four hours. A color and size difference between the two can usually be seen and measured, unless the mix contains little silt. Clay can take days to settle. I usually wait for the water to appear relatively clear. Any debris floating on top of the water is organic matter.

Unlike the loamy forest and garden soils I was used to in the Pacific and Atlantic northern areas, the soils here in the Chihuahuan desert are characterized by higher ratios of sand to clay with little organic matter. It may even have lime in it from abundant limestone. Silt is usually associated with river or stream beds. But since this entire region was once the bottom of an ancient seabed, silt can be found at various levels in all soils here.

Soil types

Soil types

After the sedimentation process, measure the depth of each layer of soil particles.  You can then determine the percentage of sand, silt, and clay in your mix. For example, if you have a 1/2 inch deep layer of sand on the bottom layer in the jar, and the overall depth of the soil is one inch, then your mix has about 50 percent sand. For all practical purposes, the ratio of sand to clay is the most important, but does not have to be exact for making adobe blocks. In other words, a window of margin is unavoidable and practical. Regardless, the clay content should not exceed 30% (or ~ 1/3 of the total ingredients) and the sand should never be less than 50%. Various opinions cover silt content, but most recommend keeping it to a low percentage, less than 25%. Strong blocks can be made from 60-75% sand and 25-35% clay.

Ribbon Test

As one gains more experience and becomes familiar with different soil types, the ball or ribbon test is a quicker way to evaluate native soils. The ribbon test is performed by kneading a ball, slightly larger than a golf ball, of wet soil in the palm of the hand. The soil should be kneaded with the fingers until it has fairly uniform wetness throughout. With the thumb and fingers, work the ball and form a ribbon.

The following guidelines can aid evaluation of the soil in the ribbon:

  • If the ribbon is long, flexible, and can sustain its own weight, it is primarily clay.
  • If ribbon is weak, breaks readily, but forms a ball which withstands much handling, it is a clay loam.
  • If the clay loam is soapy or slippery feeling, and appears powdery when dry; it is a silty clay loam.
  • If the clay loam has lots of visible sand, it is a sandy clay loam.

Now, if soil will not form a ribbon and presents a broken appearance:

  • If wet soil is friable, somewhat gritty and sticky, and the ball handles without breaking, it is loam.
  • If the dry soil feels soft and floury, when wet it feels slippery, and the ball does not break, it is a silt loam.
  • If sand is visible and the ball cannot withstand handling without breaking, it is a sandy loam.

Obviously, if the soil is loose and single grained, if individual grains can be easily seen, and the aggregate ‘ball’ crumbles when touched, it is sand.

I did a quick ball and ribbon test after wetting a handful of the black arroyo soil. I let it sit wet for about five minutes and then worked it in my hand. The ball was gritty and slippery at the same time. But I could not differentiate if the latter was attributed to clay or silt. So I did the third way to evaluate soils for making adobe blocks: I made some test blocks.

Let’s Make Blocks!

Sand and aggregate convey strength to adobe block and clay is the binding agent, the ‘glue’ blinding all the sand and aggregate together. Because we plan to use semi-stabilized blocks (for weatherization) for most of our structures, I added a level shovel-full of cement to a five-gallon bucket full of the dry arroyo mix in the wheelbarrow. I added water and mixed well, recalling my instruction on mixing cement and mortar several decades ago when building my Maine cabin. My mix had a wetter consistency than what Ed usually uses for his blocks. I remembered that Helen, of New Mexico Earth Adobes (Alameda, NM), explained that their adobe mud is poured slightly wetter than what we have seen elsewhere. The mud is pliable, flows into the four corners of the molds and requires little to no packing or floating on top. When adobe mud is too dry, it is not pliable, requires hand packing, and the block may cure with a honeycomb effect (voids in the block). The wetter mud can set up in the forms for an hour or more before the forms are pulled off.

One important task I neglected to do before pouring the mud into the forms was to thoroughly wet the forms. I paid for this negligence later; the mud stuck to the inside wooden surfaces. I had to use a large knife to coax the drying block edges from the wood and they cracked in the process. After that, I now soak the molds in a trough of water right before using.

The next morning when I inspected the blocks, I was disappointed when they crumbled easily in my hand. Too much sand and not enough binder; clay. The slippery texture of the test ball and ribbon was mostly likely silt. So it was back to the adobe mixing for another try. This time, I needed a good source of clay. I planned to recycle the three blocks I made providing sand by adding it to a mix of a higher percentage of clay.

Ed and I went out on the Kawasaki Mule with an empty five-gallon bucket and scouted for a source of clay. Not an easy task in an area that is mostly limestone, sandstone, gravel and sand. But we did come upon a small hillside that looked promising. After returning with 3/4 of a bucket full, I went to work. With the two forms, the double and single molds, soaking in a trough of water, I screened the bucket full of new mix with a 1/4″ screen on top of the wheelbarrow. I noticed that exerting some pressure on the aggregate pulverized it into smaller pieces. Surprisingly, only a small amount of large aggregate was discarded and the colors were interestingly dark brownish-red to rosy pink. Even small flat and angular crystals could be seen. ‘This should be interesting,’ I thought to myself.

I pulverized one of the volcanic sand blocks in with the newly found clay, added a half shovel of lime and water, and began mixing. The wet color was an interesting rosy color despite the added dark sand and gray cement. When it looked well mixed, I retrieved the two forms to lay on cleared gravel and shoveled in the adobe mud, although the mix only filled two and 1/2 molds (2.5 blocks). I was pleased at how well they filled the mold corners and edges with minimal hand packing, and the tops were like poured soft ice cream.

Small cured test brick from new clay source.

After an hour and 1/2, I pulled off the forms easily and the blocks retained their shape well. The forms were washed and brushed clean to dry for the next batch. If these turned out good.

The next morning was a treat when I examined the blocks. They were solidifying nicely and felt dense without any crumbling. And they were a beautiful light rosy blush. I immediately decided this was going to be a good mix and it was time to get more of this clay! We returned to the same hill with two five-gallon buckets. I screened one bucket at a time and added one of the crumbly blocks from the arroyo (which were now getting more difficult to pulverize) to each batch. Ed helped me mix this time (tough on my low back) and we made three blocks from each bucket of new clay. We let the blocks sit in the molds for an hour before pulling off and returning to their water bath. I think they would have done better to sit for another 30 minutes before pulling the forms, so we let the last batch sit longer.

We stayed the weekend at Cedar Springs with Randy and his dogs, enjoying company, sharing meals and stories around the campfire. Before leaving, I placed the blocks on their edges inside the large metal building to protect them from weather and animals. We retrieved the blocks a few weeks later (Thanksgiving weekend) and stacked them under the the ramada at El Punto where they will have the special privilege of being incorporated into the arched window. They are still strong and beautiful; an aged beige with a rosy blush, and I can’t wait to make more.

One helpful addition to the adobe tool set would be a cement mixer!

Blocks from the new clay source.

Plaster with teeth

17 Nov Plaster expiment

Serendipity sometimes proves to be a pleasant surprise. One day while we were El Punto doing other things, we took a break and tried making a sample of plaster from resources within our own tract of land. Ed had some sifted clay in a bucket. We also had a bucket of screened sand. The barrel under the gutter for the ramada roof was full of rain water. Then we strayed from convention: we shredded several dried leaves of lechuguilla, a prominent succulent in the Chihuahuan desert.

Bowl of clay, sand and water, lechuguilla fibers, dried leaves below.

Because of last year’s drought, many plants  throughout the northern Chihuahuan desert suffered a high mortality. Frankly, the desert in Big Bend region looked parched. Prickly pear cactus and lechuguilla were the most hard-hit and many have still not recovered with this year’s high rainfall. Thus an abundance of dead lechuguilla leaves are all around our place. Knowing that indigenous peoples used to pull apart the fibers of of this plant to make rope and sandals, we spent an hour pulling fibers to make a small pile to add to our plaster mix. In place of straw, which is conventionally used in cob and plaster mixes, we experimented with using what we had ready access to.

When adding the fibers to the wet mix it could not really be differentiated from thin straw. We proceeded to hard trowel the mix with fibers onto the exterior of a few of adobe blocks that form the west wall of the ramada. Even the wooden trowel was made at home; Ed sourced a few wood board scraps and fashioned a nice handle. Pushing hard on the plaster to work it into the adobe surface and joints, we stood back and hoped for the best.

Plaster after 12 hours of application.

The next day  I checked our plaster experiment and photographed it before leaving. Considering that it was applied in the heat of the day and sunshine, the cracks were few and not deep. The lechuguilla fibers seemed to impart a subtle black stain on the plaster surface, which Ed wasn’t pleased with. But I reminded him that time will tell if the stains are permanent.

A month later I checked our plaster experiment. Completely dried, the dark streaks had disappeared and the cracks remained superficial. Nor could I pull any of it from the surface of the blocks! It remains firmly attached. I posit that if the raw plaster had been applied under more favorable weather – i.e. cooler temps and not in the direct sunlight – cracking would have been greatly reduced.

As for mass production of this mix, using dried lechuguilla would probably be nearly if not completely prohibitive. We pulled the fibers and ripped them from the leaves by hand. Straw used in plaster is usually chopped to fine fibers by running through a hammer mill twice. Considering the strength and tightness of lechuguilla leaves, it would take a large and sturdy hammer mill to reduce the leaves to individual short fibers. We will probably stick with straw for our plastering jobs in the future.

Lechuguilla plant (Agave lechuguilla). Note the dead and dried leaves at the base.

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