During the summer drought of 2012, with its unrelenting temperatures above 100° F (+40° C), myself –Doug Crouch– and fellow branch of the TreeYo, Eva Wimmer, built a Cob Oven as the cornerstone of the outdoor social/cooking space at Confluence Forest and Farm in Northern Kentucky, USA. The project last year took us about two weeks. We worked on and off with full days being rare because of the oppressive heat as we camped on one of the perched ridgetops above the lake. This year we have also been working for about two weeks on the next phase of implementation amongst other tasks.
Bill Mollison and simple observation suggest, that kitchen space should be removed from the house in tropical locations to prevent the house from overheating. Simply put, the Ohio River Valley is the jungle for months on end during our fuller illumination periods. Eva affectionately refers to it as the “Green Hell” with the chiggers and mosquitoes, the humidity and the snakes. I simply refer to it as one of my homes as the property of Crouch’s Treasure Lake has been the project of my grandparents and family at large for the last 30 years and I hope to keep it going over the coming years as it transitions to the next generation. With that, we need more cooking
options besides the cob oven to really make the space functional. The next logical solution pointed towards a rocket stove for stir-fries and boiling water for tea.
Rocket stoves are a set of principles designed for improving combustion efficiency and heat transfer efficiency: Since hotter fires burn more efficiently, the combustion chambers in rocket stoves are insulated and no mass is used around the pot in order to transfer the heat into the pot and not into the stove itself. For a fire to burn hot, it also needs good air draft, what you improve by a small opening in the feed tube, a shelf in the opening and a grate under the fire. For optimal heat transfer into the pot, you will need a “skirt” around to pot to force the hot gases to scrape the pot. Correct proportions are recommendable to maintain the cross sectional area throughout the stove for best efficiency. Following these principles you create extremely hot fires that roar and give them the “rocket” in their name.
A rocket mass heater follows the same principles but is insofar different from a rocket stove for cooking, as it takes the hot air gases and runs them through a bench before the heat leaves the house. The charged up, high mass cob bench, slowly radiates heat outward.
With that, the design phase ensued for the overall space that is 16ft x 8ft (5m x 2.5m) in dimension under roof. At the initiating time of this stage, Anna Zisa was still here, finishing up her stint as an intern lending a very helpful hand. She helped us with the design phase since it was a new set of eyes as we had stared at the space for quite some time the year before. She also is really good with sketchup so she put the space in that design software for us to visualize it as a whole. But in honesty the little drawings on a scrap piece of paper to scale more or less, were probably the most helpful.
With that we had moved through to the conceptual phase, but firing the cob oven for the first time allowed us to move into master planning. The firing came on Anna’s last full day, which allowed us to see the flow of the area a lot more, producing some final
conclusions: Rocket stove next to the oven but with a gap for the all-important access connected to a bench for chill out space. Again the bench is not connected in the sense that we will be heating it, but shares the foundation.
So we started with the foundation, gathering our native limestone from the creek of the spillway and gravel that was washing away from our road. We dug the foundation for the rocket stove and the portion of the bench that we felt like we could handle in the coming days. This natural building development space is under an old carport that my grandfather had built some years ago but now just serves as a shelter for lawn mowers and junk (we are in Kentucky after all).
When we dig there, you have a bit of top soil and then you hit large gravel from the pad they put to support the weight of the car. This gravel becomes useful backfill since it is in relative location but the digging process is slowed quite a bit. From there we backfilled with smaller gravel, then the bigger, then tamped that down a bit to get a solid base. On top of that dry stacked stones were added to create the moisture barrier and then stones with earthen mortar was laid on.
The Earthen mortar is simply just native sub-soil and lots of coarse sand mixed together but without the straw making it a cob mix. We could use concrete but simply put has too much embedded energy in it for a simple project like this. We went up about 18” (45 cm) with the stone and earthen mortar before we applied a clay slip to the stones to make the ensuing cob layer adhere to it. From there we built up with cob so we could get a nice cooking height. This was difficult to gauge at first but with the making of the combustion chamber we were able to simulate what would be the future resting spot of the pot.
In truth, rocket stoves are quite technical, as you want to build with craft so that the maximum efficiency can be achieved. They have all sorts of calculations and ratios that I never would have thought of having been around a few places that just simply threw them together. Bless Eva’s heart as she was charged with dissecting the pdf’s from Aprovecho where she had just interned out on the west coast in Oregon. With that, we did create the combustion chamber from some stove pipe that we picked up at the recycled building supply shop known as Building Value down in “hipsterville central” of Cincinnati known as Northside. The corrugated edges of one end really helped us to fit the pieces together
snuggly making it a great score for this project.
Cutting metal is not a fun or an easy project with tin snips and a hacksaw. But after biting and chewing through it, we got our intake and combustion chamber, 1.5 proportion between them (I have hunch that the golden ration would be even better but……). From there we began to extrude the cob chamber up leaving a couple of inches (5 cm) space for the insulation to surround the chambers.
This is about as far as we got before our big Permablitz action day out at the lake to really manifest some big changes in the space. Matt Gillespie and others at this-land.org, the local non-profit for Permaculture education here in the tri-state area, organized a crew of about 15 people to come through on that day. Some were old students, some fellow teachers, some were old friends, some were college folk yearning for fresh knowledge. Many of the latter are designers in training at DAAP (Design, Architecture, and Planning) at University of Cincinnati. I have come to realize recently there is a giant bright spot in our future as these graphic and industrial designers started being influenced by green culture in their high school years and will go onto be professionals influencing great change.
With this great crew of people we did the same process of collecting, digging, stomping, and building. With so many people there, we quickly decided to go bigger with the bench. Simply put, our original plans were to small for the energetic crowd and great weather for this inspiring community action. Consequently, Eva got to teach a lot about cob and
natural building without the pressure or workshop fees as we get ready for more teaching in Portugal this summer. I helped to facilitate the cob stomping process for quite awhile along with hosting and firing up the cob oven later in the day.
Thus we got lots done on the bench and some industrious friends got some pieces of rebar cut so we could set the pot on top of the combustion chamber of the rocket stove, precisely measuring the recommended gaps between combustion chamber and pot.
We intrigued many of the locals, who frequent the bar that is on the property, and even said the pizza was quite delicious as we of course shared. It was a great way to end the day and to hear people talking about different design projects they are apart of. We are very grateful to all who participated and shared in this creative process.
There is still some work to do, even after the next days cleanup of cutting off excess cob from the undesirable bulging from cobbing when the mix is slightly too wet. We also finalized the rocket stove to a certain degree as we added the insulation and plastered the outside. The insulator was perlite covered in clay slip, which should make the burns even more efficient as we look to gain greater energy independence as this project unfolds. Moreover, I began the process of cutting metal to create the draft chamber but feel I need to read a bit more on how exactly to fix it. That’s the fun part of this all: some things you just have to figure out with a bit of research and trial and error.
Finally, in the fall and into next year, we will be building up the bench back, sculpting and plastering, and then getting into our next elements to add. Those include a grill –parilla– for charcoal cooking, benches with no backs, and counter space. We may add a griddle rocket stove but let’s see how the design unfolds. We hope to integrate solar cooking in varying forms to compliment this, as the important function of energy for cooking should be supported by many elements!!!!!! Thanks so much to everyone who helped along the way.