News from the Nemenhah Church!

The Lodge walls are constructed of Oak Posts with Light Clay/Straw Panels betweent hem. The beams are Oak and Cedar. The walls are built a foundation of Ruble Trench topped with Urbanite, effectively raising the earthen panels above grade.

Between the posts, Bamboo uprights are used, along with Bamboo woven between them every foot or so on the horizontal. Into this, Straw which has been coated with sticky, clay/sand Slip is packed.

In this photograph (above), you can see that we’ve loaded a whole lot of grave onto the sight.

What you don’t see is that between the posts there’s actually a deep trench also filled with gravel and packed in tight. The rest of the gravel was added after the trench was filled and the posts were set.

The Urbanite atop the trench is visible in this view. Also, between the posts, Bamboo uprights are set and with each layer of Light Clay/Straw Infill, additional Bamboo is set in horizontally. The effect is an eight-inch, insulated, reinforced sort of Straw/Particle Wall.

With the walls all in, except one section we left open so that we can get the wheel barrel and tools in easily, it’s time to begin the clay Render. A Render is what you call a plaster you put on the outside of a wall. The term “plaster” is only used for the inside, even if the material used is the same – just a little Earthen Construction trivia for you.

You can see how the walls went up in “Runs” – too high and they slump, too “short” and they take a longer time to go up.

Now we work thicker Clay Sip right into the Straw. It penetrates to about two inches, and also into any existing gaps or holes. When this is complete on both sides of the wall, you end up with a Monolithic Wall completely insulated with Mud-Coated Straw. Coating the straw is important because it makes it fireproof. Covering the whole thing with a Clay/Sand mixture is equally important, as, even if a fire were to start in the straw, the available air is used up so quickly that it puts itself out before any damage is done. Ingenious!

We did all this work in Late Winter and Early Spring. This is the driest time of the year where we live, and also, it’s really smart to do the muddiest, dirtiest work before the bugs (ticks and chiggers) come out!

I placed my folding chair here to demonstrate how high the Cob Bench will be.

We will sit on a bench that goes all the way around the wall on the interior. This bench will actually be a Thermal Mass Heater, in that, the exhaust from the Cob Oven, which is built on the outside of the Lodge, can be directed either out its own exterior chimney, or down-drafted through chimney pipes embedded within the Bench Mass Heater.

This is the base of the Cob Oven. It’s a large, flat Sandstone that will actually serve as the floor of the oven itself. We’ll bake our bread right on this native rock which was found right here on the property!

At the back, near the wall, you’ll not that there’s a stainless steel duct passing through the wall. This is the “Downdraft” through which the heat of the oven will be directed through the Bench Mass Heater. Right in front of the Downdraft Duct, there’s a Firewall of Fired Clay Brick. This will prevent the intense heat of the Primary Burn from totally destroying our Downdraft System.

The bricks are mortared in with standard Cob with Straw to reinforce it, and the duct is completely protected with four or more inches of cob. This will bake hard with the first and subsequent firings.

You can’t see it in this picture, but the brick is left exposed as you see it here, while the surround is built up to top of the metal ductwork. Three stones were set in the cob surround providing space equal to the actual dimensions of the duct opening. Then a flat stone was placed atop that to further protect the duct. It’s pretty thin stainless and it’s been our experience that this material will degrade to a paper-thin carbon over time. This way, even if it does degrade, the cob and stone will continue to function as the downdraft.

We poured the rest of the floor in Aircrete (insulative concrete with lots and lots of air bubbles in it) to totally stabilize the stone. The form that held the Aircrete in place was broken Lava Rock from the previous Itsipi Lodge. It forms the foundation for the Oven Walls.

Now, I neglected to take a picture of this (dumb), but we then took wet sand an formed the shape of the inside of the oven. This was tricky to do around the Downdraft because in the end the heated air and exhaust has to be able to pass down into the duct. Anyway, the big, double/domed sand castle is designed to hold up the clay exterior walls as they set. Once the walls are “leather firm,” the sand is removed, leaving a cavity in the shape of the domes.

The Double-Chambered Oven is a real improvement over the original, Single-Chambered designs you see all over YouTube. The back Dome is quarter higher than the front Dome. The Primary Burn is used to heat the Thermal Mass of the Oven, and this takes place in the back. When the Front Chimney is not stopped, the flame rises up and runs along the interior of the dome. This cools the combustion gasses ever so slightly and prevents their most efficient use. That’s why when you look at Cob Ovens that have been in use, they will almost always have soot build up above the door – unsightly, and an indication of lots of fuel actually leaving the oven. These gasses enter the Front Chamber, into which oxygen is entering through an appropriately – sized orifice in the door, and they re-ignite. The result is that nearly all the combustion gasses are burnt within the oven and very little smoke emerges through the chimney. This is much more efficient use of available fuel, and it is not polluting the environment.

Now that the Sand Form is in place, it’s time to move on to the Thermal Layer of the Cob Walls. This layer is Cob with a lower amount of sand. The usual ratio is 70% Sand to 30% Clay, into which I always add grass or other seed hulls. We have a Fescue Seed House in our town which throws away copious amounts of the fibrous seed husks when they clean the seed the harvest and sell to golf courses around the country. This fiber is strengthening to the Cob, but even better, there’s still always a lot of viable seed left in these castaways which sprout and grow. Their roots spread out in the cob wall, which is rapidly setting and drying. Little sprouts of grass appear and make the Cob look like a Chia Pet. Soon enough, however, there’s not enough moisture in the wall and the roots die. These become embedded and act like chicken wire within the wall.

The inner “Thermal” layer is made with less straw in the mix as well. This ensures that this layer heats up and holds the heat from the Primary Burn. We don’t leave this layer exposed, as it really does get hot, but without this inner, Thermal Mass, the whole dynamic would break down and bread simply wouldn’t cook. In a Cob Oven, you burn your fuel to heat the Mass. When the Heat has “Sunk In,” you remove the cinders and ash, and it is actually the heat of the oven, not the fire, that cooks the bread.
We built the oven with multi-tasking in mind, though. In our oven, there’s space at the back where the hot coals can be pushed, so that we can use it as a wood-fired bread or pizza oven, which works on principles of radiant heat from the burning fuel itself. Two different ovens in one!

The Thermal Layer averages three inches thick and you can see how there is a high dome in the back and a lower dome in the front. The chimney rises out of the lower, front edge of the front dome.

You can imagine how the flames must travel over the dome at the back and downward, crossing a ridge dividing the two domes. The door will have a space for air to enter that is the same dimensions as the chimney outlet, and the combustion gasses meet new oxygen in the front dome, but are still traveling downward when they re-ignite. All this clay heats and becomes the “Sink” which is what cooks the bread.

We then added another three-inch layer, this time containing a great deal more straw, making the cob itself more insulating. We also embedded Lava Rocks – the broken pieces that result from constant use in the Itsipi – and completely covered the inner Thermal Layer. Now the intense heat will not be a problem.

Should anyone touch the oven, or lean on it, or accidently stumble against it, they won’t be burned.
Note that I’ve supported the door with bricks. There’s a rod of Bamboo embedded in the door frame to help it keep its shape, but when you’re adding the Insulative Layer on top of a Thermal Layer, and it’s a big oven like this one, water tends to settle into the lower areas. The result is, especially when you are adding rock to the design, is that the purely cob elements will try to distort. To prevent that, and to allow the cob to set in the more or less square shape I wanted in the door, I created an “Armature” to preserve its shape and dimensions.

Armatures are important wherever slumping might be a problem. You want your cob to go up quickly so that it all generally sets at the same rate. This helps to prevent serious cracking. But when you try to raise a chimney, for example, there can be slumping if you don’t support the mass. You can see Bamboo sticking out the top of the chimney. The whole chimney is built with the bamboo supports, so that I could get the height I wanted without the base slumping. The Bamboo still visible will all be trimmed away.

Now, the Cob Oven is also a Mass Heating System for the Itsipi Lodge. We can stop the heat from escaping the oven simply by placing our very special, very round, Lava Rock on top of the chimney. The heat will not travel down into the bench that runs along the walls of the interior of the Lodge. It passes through the wall.

What you see in this picture will be embedded in the Bench Mass Heater. The only part that will be visible is the cleanout, which you can see is capped. This will actually be inset so that anyone seated in that particular space will not make skin contact with any heated metal.

The heat turns ninety degrees and downhill from the pass through point. This downhill is important, as once the draft begins it is the lower barometric pressure in the “downdraft” that moves the heat through and actually creates a “suction.” It turns ninety degrees again and lays under the poured floor. There’s a pass through from the main room, through a curtain into a secondary (cooler) space where folks with specific health concerns that prevent them from participating in the normally very hot ceremony, may sit and enjoy the ceremony without risk. The duck passes underfoot and is not at risk of puncture or other damage as people go from one room to another. On the other side of this pass through arch, the pipe now begins a gradual incline within the Bench Mass Heater. Finally, it will pass through the wall again and exit the Lodge. By that time, however, so much of the heat will have transferred to the Thermal Mass of the Bench that the exhaust will really only be some cooling steam with a very small amount (about 10% to 4%) of combustion gases and smoke.

This stove pipe system is laid atop a trench filled with Aircrete. I like Aircrete because it is solid and also insulated. We want the heat to transmit into the Thermal Mass of the Cob Bench, and thereafter into the air of the room, not downward into the earth beneath the Lodge. Part of the problem of the large, Tlenescal-type Itsipi is that there is so much mass to heat in the room. Usually, it takes the first two, and even the third session to get a good heat in the ceremony. This is especially true in the winter. Where I want to use a whole lot of stone in the design – in the bench and in the floor – and this stone cools between our ceremony days, all this cold Thermal Mass must be heated. By using the heat from the Cob Oven to heat this mass prior to the commencement of the ceremony, we don’t use up the heat of the Itsipi Stones.

Obviously, to get the heat to actually pass through the bench mass, a small hearth at the far end will need to be built – something like a very small, very simple single cob dome with a chimney right out the top will do. This will not be used for cooking. It’s only purpose is to start the convective draft that will draw the surplus heat from the oven all the way through the bench. When the bench, and therefore the interior space of the Lodge, is sufficiently heated, the stone is removed from the Oven Chimney.

While the primary purpose of the system was originally intended to heat the bench and provide for our comfort, building the system as a Cob Oven, simultaneously gives us heated Thermal Mass in which to cook the feast to be shared after the Ceremony. Here is an ages-old tradition that we’ve not been observing very much in recent years, mainly because of how our Itsipi was designed. In the New Itsipi, the Ceremonial Meal (Wahtsaht Ceremony) can be accomplished right along with our Itsipi Sacrifice Ceremony.

Next Steps: Stay tuned. The next article will follow the Bench Mass Heater Build, the small Hearth Build, the Aircrete Floor Pour, and then the Roof Build.

Heads up! The roof is a very special innovation. We will start with Cedar Rafters, which we’ve salvaged from the previous Itsipi. Atop this we’ll lay on a tight spiral of Bamboo, which will be tightly bound together and form a solid roof. We will lay a waterproof layer of two woven vinyl tarps over this, which will not be visible from the inside or the outside. When you sit inside the Lodge and look up, you’ll see Cedar Rafters and a tight Bamboo Spiral Basketwork – Beautiful!

On top of the water-tight membrane will go Long Straw Bundles soaked in Clay Slip, set in the manner of shingles – beginning at the eaves and the next row overlapping. This will provide us with a very thick, very insulated roof! To finally seal this and protect it from the elements, we’ll pour Aircrete over this “Mud Thatch” surface and let it run down from the center of the Lodge. The Aircrete is very loose and runs nicely, filling in every gap and sealing it tightly. It’s very light weight, but because it is actually concrete with a closed-cell structure, it will protect the clay/straw from our heavy rain.

Our plan is to celebrate the completion of the New Itsipi on Saturday, June 30^th (my birthday actually), and this will be special Ceremony, as two new Ministers will take Orders at that time! Come out and participate in this beautiful part of Nemenhah Observance of Ceremonial Healing!