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Building an Earth Oven, Part II: Insulation, Finish Plaster, and Cob Mosaic

Friends enjoying the hot oven

Friends enjoying the hot oven

In last week’s post <LINK>, we began exploring the build of an earth oven.  An Earth Oven is a simple structure, made of clay, sand, straw, stone, and fire brick, that you can use to cook foods in a traditional way.  Last week’s post walked you through the first set of steps for building your oven.  In this post, we’ll finish the build, troubleshoot, and talk about how to bake in your oven.  When we last left off, the oven was drying after building the dome.   What is left to do is to add a layer of insulation and a finish plaster, and then offer the oven protection from the elements (an upcoming post cause I don’t have that last part done yet!)

Insulating Your Oven!

Mixing cob insulation layer--keep on adding straw until it barely stick together!

Mixing cob insulation layer–keep on adding straw until it barely stick together!

Once your oven is fairly dry, you will need to add an additional layer of insulation to the oven.  Insulation is critical for the success of your oven, as this determines how quickly the oven heats up and how long it holds heat.  If you want to bake 10 pizzas in a row in the oven, an insulated oven may be able to do it, while an oven with less insulation wouldn’t hold the high temperature long enough and you would have to repeatedly build fires. There are a few things that work and, as I discovered, some things that don’t work, for insulation.

One of the tried and true methods for insulation is to mix your cob with as much straw as possible so that it just barely is holding together. Straw itself has a lot of holes that trap air, so a layer of mostly straw will trap air, creating insulation. You want STRAW here and not hay (straw has many long and thin shafts with air in the middle; hay is basically dried grass).  If you get creative, you can also add lots of glass little bottles to your oven to get even more insulation.  I had read online somewhere that sawdust also makes a good insulation layer–this did not hold true in my experience.  I added a layer of sawdust-cob mix and it had very little insulating properties, so I had to add a second insulation layer.  So let’s add that layer!

To do this, you will mix up your cob, keeping it a little wetter than normal.  Take clean straw and, if you can, use scissors to cut it up if it’s really long (anything over about 12″ in length you can cut down a bit).  This makes it easier to cut it.  Then you mix it in and get ready to add it all over your entire oven.

My big mistake here is that I thought sawdust would be insulating enough, so my friends and I put on a layer of sawdust (and artwork) that we ended up having to cover up.  Ah well!

For extra insulation, I also added some small bottles; these created bigger pockets of air for extra insulation.  You don’t have to do this.  I had a bunch of bottles that I was having difficulty cleaning after they had tinctures in them for a long time, so I decided to put them to use in my earth oven.  You can see that in-progress shot above–the straw insulation with the extra bottles.

Goose helpers help to mix up some cob!

Finish Plaster and Decoration

At this point, you have a fully functional, very well insulated, earth oven. Now you can turn your attention to the decoration of your earth oven, the finish plaster, and figuring out how to put a good “hat” or roof on your oven. The reason you need to think about plaster and a roof is to protect it from the elements. This is an oven made of mud, and thus, exposure to the elements for any amount of time will damage it. Until you get your finishes on, you can put a tarp over it!

You have a lot of options for finish plasters and thinking about how to protect your oven.  Lime plasters are one option–here is a good introduction to lime plaster. If you do a lime plaster, you will have a nice breathable finish that is also very protective of rain and snow.

I made a cob-based finish plaster using a higher ratio of sand to prevent cracking. You will want to mix your plaster in advance and then do a test piece on your plaster to see if it’s cracking or not.  If it cracks, adjust your ratios (particularly see if you need more sand). You will also want to include a short fiber that is very strong. A lot of people use cattail fluff for this; but, I had an abundance of milkweed pods on the property (and I was already using the seeds for seed balls), so I decided to use the milkweed fluff and that worked great.

Plaster can be applied in a thin layer. What I did was to briefly wet down the outer layer (so that the plaster sticks) and then use a trowel and my hands to spread the plaster, about 1″ thick and smooth it out nicely. Here are a few steps:

Mixing my milkweed-based finish plaster–I felt like a frolicking fairy!

Wetting down for finish plaster

Wetting down for finish plaster

After I have started my final plaster–you can see the consistency of the milkweed plaster (a cattail plaster would look pretty similar).

Because I also wanted some artwork and decoration on my cob, I used the cob plaster to shape some nice spirals.  I saved up broken plates, cups, and bowls that had broken during regular use, and then I used a hammer to smash them up and give me smaller pieces.  I embedded these in the cob plaster and used a small sponge to wipe away excess.  When the plaster dried, I went back in and wiped it away again to clean up the mosaic pieces.

I’ll show a few detailed photos of the mosaic:

In this first photo, you can see how I shaped the finish plaster and added the spirals.  The finish plaster below this is still wet; if it wasn’t, I would have wetted it and also scored it with a stick or a butter knife to give the new plaster a bit to hold onto (just like you would do in pottery).  I added cob glue/grout to the inner area and kept adding a few pieces at a time. I did this with extra cob so that things would hold firmly.

Here you can see it as the mosaic progresses.

Now I’m going in and taking a wet sponge and sponging off most of the excess cob.  If there are areas that need more cob, I add it.  The idea is a smooth presentation.

Here’s what the finished mosaic and oven looks like!

The completed earth oven

The completed earth oven

Despite my best efforts, I still had a little cracking on my earth plaster, but I’m ok with that.  I needed to do a second test, and I didn’t, primarily because it was starting to get cold and I was running out of time to complete the build!

Sheltering your Earth oven

The final step for your earth oven is to create a shelter for it.  You either need a shelter or a finish plaster( lime plaster).  In temperate ecosystems with lots of rain and snow, a shelter is your best bet.  I am working on that final step this spring,  so I’ll share more about it once my friends and I finish that part.  It has taken some time because I’ve been harvesting lumber from the property–as trees fall down or are blown down by storms, I am gathering them up to use for my shelter.  This takes more time, but it’s also in reverence and respect for this land that had been logged before I came.

Final Thoughts and Troubleshooting

My oven has a crack! Nearly all earth ovens will develop a crack somewhere. That’s ok, and honestly, the crack can tell you a lot about the oven–as you learn about your oven, you will learn to read the crack to understand the temperature, etc.  This isn’t usually anything to worry about as long as you have built a strong structure.

Shrine on the path to the cob oven (that stone looks precariously placed but it’s actually quite stable! Kind of a cool optical illusion.

My oven takes a while to heat! Yes, it does.  This is not like turning on your fossil-fuel-driven oven.  Earth ovens take time and are absolutely ‘slow food’.  Because of this, you have to spend time tending the fire before you can cook.  To get pizzas, I start my oven about 4-4.5 hours before I want to bake.  If it’s below 40, I start it 5 hours before I want to bake.  This means every 30 min, I am going to tend my fire.  That’s part of the experience.  If you aren’t achieving baking temperatures, you probably need a longer fire.

My oven doesn’t seem hot enough. Get yourself an oven thermometer (the stand-up kind) and see what your internal temperature is.

I will be sharing more details about baking in the earth oven and some cool recipes to try in my 3rd post in this series!  Stay tuned.  In the meantime, I hope that this series has inspired you to get your hands in the mud and maybe build something or help someone build something.  Blessings!

Building an Earth Oven Part I: Foundation, Dome, and Structure

An earth oven is an oven made of cob (a mixture of clay, sand, and straw) with insulating features (firebricks, bottles).  It is an extremely efficient and sustainable method of doing any baking you might need to do. One firing of your earth oven can allow you to bake different things for hours (pizzas, breads, casseroles, vegetables, etc), and it takes only a small amount of wood to heat.  We fire ours by simply picking up deadfall sticks and branches, cutting them up, and that’s all we need. An Earth Oven is fully sustainable to build and to cook with, and you can locally source literally all of the materials for the oven (and in fact, minus fire bricks, you can probably harvest everything you need from your own land or the land around you).

The completed earth oven

The completed earth oven

An Earth Oven allows you to connect deeply with the earth itself, encouraging you to slow down, root, and ground.  It is certainly a nice example of “slow time” and “slow food”, as the oven takes a few hours to fire before you can bake in it, and it requires some learning.  With that said, the rewards of this approach way outweigh any challenges you might experience as you learn and grow.

 

The other thing about your oven that is rarely discussed is that it is truly a sensory experience.  Your earth oven will allow you to bake any number of delicious creations–and when you bake in it, the smell of the bread permeates the clay itself, and it has this incredible smell, unlike anything you’ve ever experienced.  Even on cold days, being near your oven will keep you warm (and your oven will stay warm for literally hours–possibly all night).  It is just such a wonderful thing.

Fire in the near-complete earth oven!

Fire in the near-complete earth oven!

Earth ovens are a wonderful kind of “hearthspace” where we can cook foods for ourselves and loved ones, use natural materials to build from the land and honor the land, and create a very sustainable and low-input cooking method that is a joy to make and a joy to bake in.  In this new series, I’ll offer full details about how to build an earth oven step by step!  This series will have three posts–today’s post covers materials, preparing the foundation, preparing the base, and creating the dome.  Next week’s post will explore insulating the oven and finishing the oven through a mosaic/cob, finish plaster, and options for doors.  The final post will explore how to cook in your earth oven and some tips and tricks I’ve learned in my first year with the earth oven.

 

Preparation: Materials

In order to build your earth oven, you will need to prepare some materials and do some prep work.  Earth ovens are not expensive to build–most of the investment is in your own time and labor.

Materials for building:

  • Stone and urbanite: You will need some kind of base for your oven; most people use local stone or even urbanite for a strong foundation.  Urbanite refers to waste materials like broken bricks, broken concrete blocks, etc.  You can use urbanite to “fill” the inside of your base and create a stable foundation.  I have also seen people build ovens on old large stumps or platforms.
  • Subsoil / cob: First, you will need access to your subsoil (that’s the soil that is not full of organic matter, but the soil below it). You will need quite a bit of subsoil, so make sure you have easy access. Once you have access to the subsoil, you will want to do some soil testing (which I explain in the link) so that you can be sure you have good subsoil to work with.  To access subsoil here, I found a tree that had gone down and uprooted itself–the roots and ground below it was full of all of the subsoil I needed.
  • Straw:  You will need a bale of straw for your cob.  Straw adds strength, can provide insulation, and can help hold your structure together.
  • Sharp sand. You may also need some sharp sand (known as builder’s sand) depending on what your cob tests reveal. You can get this from a landscape supply or building supply place.
  • Sand: In addition to the sharp sand as an additive, you will need sand to build your sand dome.
  • Newspaper: You will need 3-4 newspapers for your dome.
  • Bottles: You will need at least 20 wine bottles for insulating your base. These can be foraged from recycling bins, saved by friends, or even found at local restaurants. Depending on your structure, you can also use smaller recycled bottles to help with insulation (I did this, but some people use an only straw).

Tools for building:

  • Wheelbarrow or cart: You need something to move materials around your site.
  • Shovel: A shovel for digging subsoil and moving cob around.
  • Screen.  To prepare your subsoil, you will need to screen it of larger items (stones, debris, etc).  For this, you can build a simple soil screener (this also works great for screening compost!).  Make your soil screener large enough that it will sit over your wheelbarrow or cart that you will be using to move it.  I built mine with scrap lumber and 1/2″ hardware cloth.
  • 5-gallon buckets: A few buckets are super helpful.  They can move cob from where you mix it to your oven.  You can fill some with water to rinse your feet.
  • Tarps:  A small tarp will allow you to mix your cob.  You might want several, especially if you are doing the work yourself (I found that when I was doing the work myself, I would gather materials – screen cob, gather rocks, etc, on one day and then build on the next, so tarps were able to keep my cob screened and protect it from the elements).  You also will need a tarp to cover your cob oven until you can have a structure built for it.
Source of clay / subsoil - a tree that uprooted during a storm

Source of clay / subsoil – a tree that uprooted during a storm

Cob screen in action - this was built with scrap lumber and 1/2" hardware cloth

Cob screen in action – this was built with scrap lumber and 1/2″ hardware cloth

Other Tools and Materials:

  • Pizza peel (I created one from an old aluminum pan and an old rake handle)
  • Firing door and baking doors (more on this in an upcoming post)
  • Shelter structure

We’ll cover these last three in an upcoming post.

Preparation: Oven Size

You can decide how large of an earth oven you want to build.  There are many measurements in the Build Your Own Earth Oven which I used as a reference.  Here’s a simple diagram of the oven and dimensions that I used.  These allow you to figure out how large of a foundation and base you need and will determine the overall structure.

For example, to get good airflow, I created an oven that was 27″ in diameter, which included an 18″ high dome.  Your door should be 63% the height of the oven, or 11.5″ high.

Your oven can be larger or smaller, of course, depending on your needs.

Preparation: Selecting a site

I think it is really important to spend time selecting the right space.  Your space needs to drain well (especially if you are in a temperate climate that has snow/ice).  Your space also needs to be protected from the elements as cob is a natural material that will weather quickly if left without protection.  Your space should also align with your landscape (see setting intentions with nature).

Your oven should be somewhere easily accessible.  You will need to tend a fire every 20-30 minutes for four hours in order to have an earth oven hot enough for pizzas or other baked goods.  Thus, you don’t want to put it so far away from your house that its hard to tend the fire (but not close enough to cause any insurance issues!)

For my earth oven, I decided to build in a little nook on the edge of the property that leads into forest.  That provided both shelter from the elements (and it will get a permanent roof this year) as well as being pretty close

Preparation: Clearing and Foundation

To build your earth oven, it begins with a good foundation. Any cob structure should have “a good hat and feet”, and the foundation is the “feet” part of that equation.  Here is step by step how I built my foundation.

I began by measuring out my foundation – 46″ based on the height of my oven.   Then I removed all of the plant material (as described in this post); I worked to replant any material that needed to be replanted, etc.

Clearing the space

After clearing, I dug down 1.5 feet and added a gravel base for drainage.  Its hard to tell from these photos, but we are on a slight incline, so I made a drainage area to the left of what you see here.

Foundation of gravel

Foundation

Preparing and Mixing Cob

The next step is to screen and create your cob.   I went to my site with my wheelbarrow and put a 5 gallon bucket at a time in my screen.  Using a rock, I worked the cob through the screen. (More details about making cob here).

Screening cob

Screening cob

After that, I moved it to my building site and prepared to mix the cob.

Subsoil screened and ready to mix!

Subsoil screened and ready to mix!

To mix the cob, you will need an old tarp, two or more buckets of water (I like to use warm water!), and some happy feet.  First create a well in the center of your cob and, just like making noodles or dough by hand, then start mixing the cob with your feet.  You can use the tarp to flip the cob and keep working it.

For building, you will want to also add handfuls of straw (I cut the straw up so it’s a little shorter) and work that in.  Ideally, you want something with a good consistency that sticks together and isn’t too wet and crumbly.  You can add more water or more soil as you mix.  I have more detailed instructions on mixing cob in an earlier post.

Mixing cob

Mixing cob

You can also get others to help you–friends, children, or even geese.

Goose helpers

Goose helpers

Building your base

In addition to the cob, you will also need something to build your base up that is fireproof and stable–rock or brick is a very good choice for you. For my foundation, I used a mixture of cob along with locally foraged stones and urbanite (old concrete bricks that were broken and strewn about the property.) A good foundation and good base are critical to the success of your oven. You want to build your base high enough that it’s comfortable for you to fire and use the oven.  I kept mine pretty low cause I like to sit on the ground when I work!

I began by mapping out a circle (using a string and some chalk) and building the outside of the circle up using the cob as a mortar.  On the inside, I added my urbanite brick pieces and filled in all holes with smaller stones and cob.  Here’s the first layer.

Building the base.

Building the base.

As I worked, I continued to build up the stones on the outside.  Since I also planned some decoration, I had stones I had already added mosaic to that I wanted to include.  These pieces were made of mosaic materials leftover from both from doing my mosaic bathtub a few years ago + broken pottery and plates that I save.

My mosaic stones

My mosaic stones

It took me two building sessions, but the base continued to grow.

Base after adding mosaic stones

Base after adding mosaic stones

You can see that I’m building up the inside of the base as I build up the outside of the base.

Base before insulation layer

Base before insulation layer

At this stage, I have the base at the top level and as high as I want it.  You can see I am using a piece of wood and a level to check to make sure everything is level as I work. The next step is to add the insulation layer to the base.  The insulation layer is made up of a straw-rich cob combined with wine bottles.  Bottles offer insulation, which keeps heat from getting absorbed by the stone below.  Insulation is really an important feature of these ovens–investing the time to do insulation will allow your oven to be used in colder temperatures, hold heat longer, and heat up sooner (meaning you use less wood to make that happen).

Thick layer of cob in base

Thick layer of cob in base

I started this with a thick layer of straw-rich cob. Straw itself is insulating as it traps small amounts of air in it as it is worked into the cob.

Next, I layered the bottles with more cob in between each to create a solid foundation.

Bottle insulation

Bottle insulation

Here’s the bottles with more cob added

Bottles getting covered

Bottles getting covered in cob

After the bottle layer, I used the board to smooth out the layer and wait for the base to dry about a week before continuing.

The base is done!

The base is done!

Except that we have powerful raccoon activity, and that night, someone tried to dig up my base to see what was in the bottles!

Coon activity

Coon activity

I repaired the cob and then started putting a tarp over it at night to deter the raccoons until my base was a bit more dry.

Laying your firebrick

Firebrick layout

Firebrick layout

To start your hearth, you want to put down a fresh layer of cob so that you can set the bricks in carefully.  Slide the bricks against each other and make everything perfectly level.  To make an oven that is XXX” inside (which is enough to cook a few breads and two small pizzas, perfect for small groups or families) you can use fifteen firebricks in the following pattern (the two firebricks in the back were redundant and I removed them later).

Notice here that I’m also planning a lip to pull my pizzas in and out of the oven.

Circle for dome

Using a string, I made a circle to show me where to build the sand dome for the oven itself.   Now I’m ready to build the actual oven.

Creating Your Sand Dome

I think the most labor-intensive part of this entire process is building the dome and cobbing the dome. Everything else can be done in stages, but this really has to be done all at once. This part is a great time to invite some friends or family to help you if you are doing this on your own.

Start by mixing 1-2 large batches of cob (with straw reinforcement) and tarping that while you build the dome.

To build the dome, you will want a ruler (to test the height of the dome), newspaper, and a few wheelbarrows of sand.  I mixed my sand right in the wheel barrow and got it to a consistency where it would build up well.

Mixing the sand

Mixing the sand

Building the dome

Building the dome

So then, start building the dome, using the guide you drew.  I stuck a metal art ruler down the center of the dome so I would know exactly how tall it was (with a goal of 18″ tall).

As you get further along, you can take a small board and smooth and shape the sand dome.  PUll out the ruler, and you are ready to build!

The completed dome

The completed dome

Go head and coat the whole sand dome with a layer of thick wet newspaper (this creates a barrier both to keep the cob from sticking to the sand and gives you a sense of where to dig out later.

Now, you want at least a 2-3″ thick layer of cob all around the dome.  You dont’ want to press the cob into the dome, but rather, shape the walls downward with your hands.

Building the oven

Building the oven

Keep working your way up.

Oven build continued

Oven build continued

A lot of ovens have some kind of door area. We used old bricks to build our door area (planned out in advanced).  To keep the door balanced, we added two pieces of packing foam that we cut to the right size.  These were later pulled out when the structure was dry.

Building the arch

Building the arch

The arch proved a bit tricky–we layered sticks in between the sand dome and the foam arches and that provided enough stability until the oven dried.

Here is our completed first layer of the cob oven.

first layer of cob finished!

first layer of cob finished!

At this point, you will want to give your oven some time to dry.  We put a little pavilion over it and allowed the summer sun to dry it out.

Digging out the oven

The next step is to dig out your oven and light a few small fires to help dry out the inside of the oven. You can just use your hands, a small trowel, or a stick.  You want to be careful as you dig out so that you are not digging into the cob itself (hence why the newspaper barrier is so useful).

Digging out the oven

Digging out the oven

I used my shovel to remove the bulk of the sand and then got in there with my hands as I got closer to the walls. I let the oven sit another week after I pulled out the sand, and then I lit a small fire for a few days to get the inside dried out.  Here’s the very first fire.

First fire

First fire

Alright! That’s over half of the oven build.  In my next post, I’ll show how I added layers of insulation, a final plaster, and also decorated it with more mosaic pieces that were salvaged from broken pottery.

Goose helpers and the druid builder!

Goose helpers and the druid builder!

One final thing I want to say now is this is an incredibly good way to connect with the element of earth.  There is nothing more grounding than having your feet and hands directly in the soil, shaping it, honoring it, and getting to know it.  I really enjoyed my time building this and felt incredibly grounded afterward!

Building with Cob, Part I: Project ideas and Honoring Earth

Making some cob!

Connecting with the earth can mean a lot of things–and today, I want to talk through how to create a simple building material that can be used for a wide variety of purposes: cob.  Cob is an ancient building material that is a combination of sand, clay, and straw (or other strengthening materials) mixed with water. Cob, the synthesis of water and earth, becomes the passive forms through which we shape anything from a small earth oven to a whole living space.  In this post, I’ll introduce cob and offer some different kinds of projects that you can do with it. This post compliments last week’s post, where I shared how to make ecobricks from waste plastic materials.  Cob is certainly one of the more sustainable and local construction materials to use in conjunction with ecobricks, so I thought it would be a nice time to introduce this as well.  I’m also going to be doing a variety of cob projects on the homestead in the next few years that I will share about, and thus, it is useful to have this introduction first!

 

For many years, when I was studying natural building and various kinds of sustainable living at Strawbale Studio in Michigan, I offered a series of posts on natural building topics and rocket stoves. This post continues that series, and I am delighted to revisit some of these construction techniques. This post will serve as a basic introduction to natural building with cob–for more resources, there are books and classes (I’d highly suggest one of the internships at Strawbale Studio for a hands on experience!) Today’s post covers the preliminaries for cob building – what cob is, the kinds of projects you can make with cob, and the spiritual implications of learning to work with this amazing material. Next week’s post will show you how to test your soil and make cob.  Once I finish it in a month or so, I will also show the cob/cobblestone build a simple passive solar greenhouse heatsink wall.

 

Connecting to the Earth

Cob is the combination of sand, clay, and straw that has been used as a building material throughout the ages.  It is a most ancient building material, an ancestral building material.  It is always a local resource that reflects the different qualities of the earth in that location. It has been created by humans for thousands of years (if not longer), and is used in a number of building techniques, including adobe construction, waddle and daub construction, strawbale construction, and much more. In fact, nearly every temperate or tropical non-industrial culture has created their own version of cob in some capacity. This is a building material that is right from the land, created with our bodies in perfect harmony with the living earth.

 

In modern industrialized cultures, we often live in and build structures in opposition to the land. These structures almost always ignore basic things like sunlight, wind, or other weather patterns that would make heating and cooling them more effective and instead, rely on unsustainable fossil fuel burning to make them comfortable.  We live in houses full of toxic substances: the materials were toxic to the land and her peoples (human or otherwise) during extraction, toxic during their production, and they will be toxic when they are destroyed and put in a landfill. Our homes, structures, and building materials are thus in a constant state of disconnection from the living earth.  I think its hard to live that way, even subconsciously, and not experience some disconnection as well.

 

Cob offers us one path, of many, back to more nature connection.  Learning some cobbing and other natural building skills can help us connect with the earth, honor the earth, and learn some of the deeper mysteries of the land.  We can reconnect with the wisdom of our ancestors, who built shelters and homes right from the land aroudn them.  Learning to make cob, even through small things like making cob candleholders, allows for that deep, ancestral connection.  There is nothing as satisfying as communing with the earth, digging up some of her subsoil, sifting it, and stomping it with your bare feet to mix it into something that you can use to create virtually anything!   The mud between your toes, the weight of the earth, the shape of it in your hands–it is empowering, it is connective, and it is soul-filled.

 

Making cob and building with cob (also known as “cobbing”) also offers powerfully to the druid elements (which are explained here): particularly, the synthesis of gwyar and calas. You can also think of cob through the classical elements: the passive elements of water and earth are combined to build structures which heat, shelter, and allow us to cook meals, and so on.  It is an incredible and beautiful way to learn to live more in harmony with nature.

 

In the 21st century and the age of the Anthropocene, I think we need multiple pathways to find our way back to the cradle of the earth.  To a place of connection, or re-connection. Of learning that the earth, right under our feet, and the living things around us can truly provide all of our basic necessities for life.  This is a lesson that humanity has forgotten in the century+ past industrialization, but it is time that we begin to learn this lesson anew.  And for some of us, this lesson comes in the form of learning to build as our ancestors did–of using materials right from our land.

 

What are the benefits of working with Cob?

The Strawbale Studio - Cob/Strawbale with Thatched Roof

The Strawbale Studio – Cob/Strawbale with Thatched Roof

Local and sustainable sourcing, ethical building material. Because cob is locally sourced, it is an extremely sustainable building material. If you have the right kind of sub-soil, you can literally dig it out of your land and make it right there. Some sub-soil may require off-site amendments, depending on the nature of your soil (see soil tests, next week’s post). Cob comes right from the earth, and can return right to the earth, with minimal to no ecological impact. For example, in digging my hugelkultur beds, I replaced hard packed clay with large amounts of wood, plant matter, and compost–and the clay that was removed from those beds was piled up nearby, ready to be turned into cob.  Now I have a giant pile of subsoil that I am slowly using for new cob projects.

 

By comparison, modern construction materials are just awful from an environmental perspective. For example, the production of concrete is the *third largest* producer of C02 in the world! The link in the last sentence shows at how many different stages the production of concrete is linked to C02. Yes, concrete is more permanent than cob, but it comes with serious disadvantages.

 

Endless possibilities for construction. The possibilities of building with cob are endless! You can build earth ovens, chicken coops, candleholders, and even whole living structures. About 10 years ago, strawbale/cob construction was listed in the International Building Code, which makes it easier to secure the necessary permits in places that require them. Most of the “finished” photos in this post are from the Strawbale Studio, built by my natural building mentor, Deanne Bednar.  In addition, unlike many conventional building materials that require squares and rectangles, cob also allows for amazing amounts of versatility and creativity.  Unlike regular structures built with straight lines, cob allows for flowing curves, circles, spirals, and many unique features. Thus, many natural building projects are flowing, curvy, and fun.

 

Accessible to everyone. If you didn’t grow up “handy” or had someone to teach you, traditional construction may be inaccessible–both because it requires a lot of specialized knowledge and also because it requires multiple kinds of expensive tools and supplies. By comparison, cob construction can be taught to anyone, including children. In fact, cob allows us to build things right from the land, on the land, with minimal hand tools and no fossil fuel demands. It is perfect for group settings, schools, and other places where people want to join together to do something fun.

 

The inside of Strawbale studio with curves and beautiful features

The inside of Strawbale studio with curves and beautiful feature

Building with cob is “slow” and “meditative.”  Taking fossil fuels out of the equation requires a different kind of time commitment. Fossil fuels allow us to radically increase the speed at which things are done, but not the quality by which they are done.  Cobbing allows us to slow down, to re-attune with earth’s rhythms, and to have fun making something magical with our own hands and feet!  This is “earth time” and requires us to simply embrace the experience. Creating and working with cob is not done on “fast time” but represents a very slow and meditative process.  I list this as a benefit because I truly believe it to be so–by attuning with the earth and her building materials, we are forced to slow down, breathe, and be a participant in the process.

 

Can be combined with other sustainable practices. Cob is but one of many different techniques that can be used to build material. Timber framing, ecobricks, thatching, passive solar, rocket stoves/energy efficient heating, and shingle making from wood are just some of the strategies that align with these approaches. A rich universe of knowledge awaits you down this path!

 

Example Cob Projects: Rocket Stoves, Ovens, and Structures

One of the first considerations when thinking about a cob building project is matching the cob project to your climate. In arid climates where there is little rain, cob can be out in the sun and elements unprotected with minimal damage. In temperate climate with lots of rain, sleet, hail, and snow, special considerations are needed to protect the cob from the elements. In particular, cob designs need to have a “good hat” and “good feet.” That is cob projects are required to have some kind of protective structure that prevents the cob from getting wet–even with a finish plaster, it cannot stand up to the regular elements for extended periods.  A good footer,  usually made of stone, is what you rest cob on (so that it can’t wash away). This is one of the big differences between concrete and cob. Concrete is designed to stand up to the elements for years–but it also means that it will not return easily to the earth. Cob requires more TLC with regards to the elements, but is perfectly fine when designed correctly. As you see some of the examples of cob projects, you will see the use of the good hat/good foot design!  With this in mind, let’s explore some of the wonderful projects you can do with Cob!

 

Cob Ovens for Pizza and Baking. A staple in the cob world and a project that can be complete over several weekends is a cob baking oven for pizzas.  This is a good beginner project for cob, and there are lots of designs and resources online and in print.  I’ve built a few of these and have also had the pleasure in cooking in them!  The pizza that comes forth from them is amazing.

A cov oven at Sirius Ecovillage

This first photo is of the cob oven at Sirius Ecovillage (where I was blessed enough to do my permaculture design certificate in 2015!).  I love this oven because it has a well-designed structure that lets light in, it has beautiful artistry of the oven outside, and it produces quite tasty food!

 

Cob oven with fresh mushroom pizza

Earth Oven at Strawbale

This second oven is located at Strawbale studio.  While this oven was built before my time there, I was able to help repair cracks in this oven and bake in it on several occasions.  This oven did not have the optional stove pipe (like the first one did) but it still worked great.  In this case, the venting of the heat and smoke just come out the front. Notice the “hat” and ‘feet” of this design. The first photo shows some handmade pizzas with fresh foraged mushrooms we made and enjoyed as part of a workshop!

 

A Cob Rocket Stove or Rocket Mass Heater: Cob is excellent at transmitting heat (or cold) and because of that, it makes an excellent material for a rocket stove or rocket mass heater. There are lots of different designs for these; some years ago I detailed one rocket stove using a cob mortar here that I built with a group of others at Strawbale Studio. Other designs include indoor ones that are designed to heat larger spaces, like this other indoor heater at Strawbale.  This cob bench works on the principle of heating bodies, not spaces, so it radiates heat out.  It takes a long time to heat up (about 4 hours, as the cob is 4″ thick in most places) but even after the fire dies out, it will stay warm for many hours.

Indoor rocket mass heater

Indoor rocket mass heater at Strawbale Studio

Rocket stove with cob mortar

Rocket stove with cob mortar

Larger Structures: Buildings, Walls, and More: Cob projects can become any size you are willing to work on–up to full size houses, saunas, chicken coops, and more. Strawbale Studio has a lot of such examples of these kinds of structures. One of the keys to thinking about larger structures is that cob transmits heat or cold really well–this means that a stove will move heat outward. However, uninsulated cob walls will quickly turn into a freezer in winter–this is why cob is often combined wtih strawbale construction for strawbale’s insulation properties in temperate climates.  Cob on its own has no insulation and will move heat or cold through it.

Hobbit Sauna

Hobbit Sauna tree (this is a tree I designed and created for the sauna with help from my friends!  Here, the tree is drying after working on it for two days. This was done during my last visit to Strawbale Studio in 2017!)

 

In Greenhouses and as Heat Sinks.  My current in-progress cob project (which I should finish by the end of Fall 2019) is a cob/stone wall for the back of my greenhouse.  I am doing this project in my small repurposed carport greenhouse. All greenhouses have three sides that allow for light and heat to enter (east, south, and west).  The other side of the greenhouse, north, never has direct light or heat coming through it, and thus, it is better to insulate it than to treat it like the other three walls. Because cob is an excellent conductor of heat, I am using the wall as a heatsink. This will be useful for any sunny day in fall, winter, or spring where the sun heats the greenhouse up considerably but the temperature drops a lot in the night (in summer, sinking heat isn’t a problem!).  I’ll share this design in a future post.

 

Cob benches and smaller structures. Cob is also used for a variety of smaller structures, such as cob benches. These can be done indoors or out. I haven’t yet worked on one of these projects, but you can see nice examples here.

 

That’s it for today–in my next post, we’ll look how to test your soil for an appropriate mix of clay and sand, mixing cob, and doing some basic construction (in this case, my cob greenhouse wall). May your hands ever be in the earth, may your heart ever be full, and may your spirit ever be inspired!

Natural Building I: The Strawbale Studio

Yesterday, I attended a rocket stove building workshop at the Strawbale Studio and the sustainability-focused work of Deanne Bednar. In this post, I want to spend time highlighting the Strawbale Studio and Deanne Bandar’s work as an excellent example of permaculture and sustainable living.  In this first post, I’ll highlight some of the Strawbale Studio and other projects; in a later post this week, I will talk specifically about the rocket stove concept and what we learned and built!

I want to start by saying that site visits to places like the Strawbale Studio are really important and inspirational for anyone who is interested in natural building/sustainability/permaculture.  These places can bring us inspiration, joy, and ideas for transforming our own landscapes.  I’ve read about all of this in books and spoken to people, watched videos on Youtube, etc.  But its not till you really get to see it, and build it, that you really understand its power.  Its through being able to put your hands on the cool cob, or see the thatched roof from different angles, that you really appreciate the value of natural building skills.  I have been inspired by the Strawbale Studio and Deanne’s positive energy, and I can’t wait to get started on some of my own projects.

The Strawbale Studio

Deanne runs the Strawbale Studio on her rural property outside of Oxford, Michigan (in South-East Michigan).  Deanne runs regular monthly workshops, full moon potlucks, and regular volunteer days on natural building.  She has learned from a number of excellent teachers, including Ianto Evans. I feel incredibly fortunate to live so close to someone with such expertise on natural building–she is truly a wealth of knowledge and an inspiration.

I didn’t get to take pictures of everything because we had quite a rainy day, however, I did get some photos to share and will return for more when the weather is nice!

The Strawbale Studio

 

Strawbale Studio Back

The first two photos are of the strawbale studio.  Its a fully functional living space built out of natural materials–namely, cob (which is a mixture of clay, sand, and usually straw) and strawbales.  It also features natural thatching from phragmites (which are what many consider an invasive species in the area; its nice to see what Deanne was able to do with these reeds!).  These next three photos are of the inside of the strawbale studio. One of the things I really like about cob building is how you are able to be so creative with it!

Strawbale Studio Tree!

 

Inside the Studio #1

 

Strawbale Studio Loft

Sleeping Spaces, Living Roofs,  & Building Materials

Deanne brings in interns from all over the world to live and work at the site, learning natural building along the way.  They get to sleep in really neat places, like this natural lean-to and the strawbale studio!  And in the house… if they really want to. (But seriously, who would want to when you can sleep in these kinds of places?)

Thatched Lean-To

 

Living Roof – In progress

 

Natural Building Materials

Cob / Earth Oven

The next photos are of Deanne’s earth oven.  I’ve been planning to make my own for some time, so seeing a live one and being able to look at it and talk to her about the process was super helpful!

Small oven mockup!

 

Earth Oven!

 

Awesome Stick Spiral above Oven

Cob as a natural building material has so much potential. In Michigan, we have a really nice balance of sand to clay (which is about 75/80% – 25-20%) so we have great materials for cob here.  I am looking forward to making some of my own here next year :). Here are two more shots of what you can do with cob–as a decorative feature and as a building block:

Cob spiral

 

Brick of Cob

Food Forests

Deanne also uses permaculture principles to grow food and medicinals. Here’s a photo of her front “lawn”.  Love it!  This is a front yard that produces rather than consumes. And in the fall, its so beautiful with all of the colors and plants!

Food Forest!

 

Food Forest!

I am truly inspired by Deanne’s property and all of the projects happening. I think its important to remember that this  is the product of thousands of hours of work, many helping hands, and a woman with a clear vision for a sustainable future.  Her projects and presence in this community is something worth aspiring to. This is the power of community, knowledge, and action!