I’m fascinated by new ways of making cob. Especially ones that take some of the back-breaking labor out of the equation. Years back I visited HUG, or Hunt Utilities Group and produced a short video of the experience. Ryan Hunt gave us the tour and explained their vertical auger mixer. Which can make quick work of cob creation in mass quantities. Recently I checked in with HUG to see if there were any new innovations with mechanical cob mixing. The following is a email I received from Ryan…
The magic to it is the vertical auger. Tumble mixers make balls of it. Mortar mixers and others with blades running through the mud catch the straw on the leading edges where it builds up huge sometimes. Horizontal augers can compact the material against the side. Skidsteer or tractor mixing is inconsistent. And feet just get tired by the time you get a couple tons done.
We started with the big, blue Patz vertical Auger mixer. It’s called a TMR mixer (total mixed rations) and is usually used for cattle feed. We bought the small one made to be run by a 100hp tractor. It mixes up to 7000 lbs of cob in about 30 minutes.
Then we bought and modified a little orange mixer hopper meant for spray-able, fibrous mixes. We modified it with a vertical auger to replace the paddles and added a variable speed motor. It has been used extensively to make small batches for the cob sculpting on campus.
With those two, we decided we needed something of an in between size that could be more portable than the big one, but make enough cob to be useful on a job site. So we commissioned the construction of one about 1/4 the size of the big blue Patz. That is now powered with a small tractor.
These are all successful, but are now underutilized. We may be willing to rent some out. Last year, we made several tons of cob for a local builder.
Then we have a gravel screener to get the rocks out of the sand and the clay (somewhat). Cob with only small rocks works well for being pumped and trowel applied or spray applied on a wall. We have a nice little pump and air compressor set up that can do that job, too.
We’d love to have some help documenting “commercial” cob. It’s not the main direction we are headed at the moment, but there is a lot that we can share with people.
Mixing cob… mesa style. This is a sloppier version of cob that’s good for infill, shaping and scratch coat plasters. Raw earth, straw and water. I’ve been using this for everything lately. In the video it shows a sloppy mix as it comes out of the mixer and the same mix after it has sat out in the sun and the wind. It stiffens up quick. I’m a fan of the cement ( cob ) mixer. It allows you to do several other things while the barrel is spinning. Electricity can come from variety of sources. Of course using power from the sun to make cob would be natural building nirvana. Even better… the human power of friends and neighbors.
It’s about that time of the year again. The weather is warming up and the mud is almost thawed. Fortunately in the high deserts of New Mexico there is plenty of good dirt around, especially in the mesa, where sometimes there’s too much mud! Plain old mesa dirt mixed with straw creates a delightful earthen plaster.
I want this southern wall to be mostly cob and earthbags to collect the warmth of the sun. Of course, it would be wonderful to have a pure cob wall, but time does not permit. And after all that’s slow! Here’s the thing though – It’s already cold. I’m pushing my luck with light clay infill. The light clay takes a long time to dry. Even in warm weather you should let the light clay infill dry for a couple of months before plastering. Cob too. It won’t dry in time. Basically, I’m after a wind break for the winter so I can work inside.
Light Clay Cram
It’s somewhere in between wattle and daub and light clay infill, but it not really either. I’m making use of my post and beam structure by nailing saw mill ‘waste’, known as mill ends, to the posts. This creates a good lattice for what comes next.
I made some light clay and let it sit out in the sun for an afternoon. The earth absorbed the excess moisture and the clay gets pretty tacky. I took a lump of light clay and placed the in between the open space between the mill ends and cram it over to the side. Packing and pushing. The lump of light clay fills the gap and hangs over the mill ends both inside and outside. I just kept doing that until the openings were full. Let dry in the feirce winds…
After a few days of sun and wind it was time to add mud. I tucked earthen plaster in the gaps and covered the light clay. The straw creates a good key. Now when I go back in the spring to add the infill plaster the wall is ready and I have a wind break for the winter.
This has got to be one of the quickest and low cost ways to create a wall. Rather than building up slowly this allows for the wall to go up first and then thicken up later. The wall is up. The materials were cheap. And the amount of human energy was moderate.
I had to fill a space in a strawbale wall above the bales and betwixt some rafters. I had filled the space with some light clay a year ago, but it was wet and never dried resulting in decay. The light clay could have worked if it had a chance to dry over the warmer months, but I placed it in the wall during fall so it didn’t get a chance to dry. In the spring I ripped the rotting material out and left the cavity empty. The only thing between the inside and the outside was a 4″ cob wall attached to a 2 x 12″ wood stud – which does the trick, but in the winter months collects frost.
This fall I just wanted to fill the cavity and provide some insulation to the upper part of the wall. The choices were to create small bales that would fit into the the spaces; try more light clay ( this time drier ), or pack some poly-propylene bags with straw and stuff it. I choose to use the bale bags this time. Continue Reading…
We started with the big, blue Patz vertical Auger mixer. It’s called a TMR mixer (total mixed rations) and is usually used for cattle feed. We bought the small one made to be run by a 100hp tractor. It mixes up to 7000 lbs of cob in about 30 minutes.
