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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!

Earthen Nature Spirit Statues with Cob

An earth spirit statue in my greenhouse, freshly made with sticks and an oak gall

A lifetime ago, myself and a dear friend dug some clay out of a hillside.  We each took half of it.  My half of the clay was used to form an earthen statue, a guardian statue, for that same friend who was struggling with terminal cancer while still in his early 20’s. It had a wooden tree knot head, stones for its belly, a stick staff, and an earthen body.  My friend accepted it reverently, and it went with him everywhere, even till the end. As he struggled with his battle with cancer, it grew nicked and chipped.  The wooden head fell off, just as my friend’s brain cancer grew more serious. When he passed on, the earthen statue passed on with him, returning to the earth. This statue was an impermanent being; fashioned of unfired clay. It was brittle, yet, in its own way, full of strength. It was ephemeral, and yet perfect in its lack of permanence.  It was a spirit statue, channeled from nature, with a bit of spirit within it, there to help my friend on his journey.

 

I had forgotten about this small statue until quite recently.  I’ve been cobbing several times a week, working to get my back greenhouse cobblestone/cob heatsink wall done.  One day, I had just a little cob left over. Not enough to set more stones on the wall, but enough to play with.  I started to shape it and felt the power of the Awen and of spirit flowing through me.  I saw a vision of all of these earthen statues, shaped, with sticks, shells formed and strong. I saw them left, to break down quietly in the elements and return to the earth with her blessing. And then, I remembered that earthen statue that I made all those years ago to try to provide healing and strength for my friend. And so, I’ve been experimenting working with such earth spirit statues. After sharing a few of my photos with friends, several suggested that I write about how I make these and how I use them ceremonially.  So today’s post, part of my cob building series, looks at the process of making earthen nature spirit statues all from simple materials found in your local landscape.  This is something that ANYONE can do, regardless of artistic skill.  So let’s get muddy!

 

Ephemeral Sacred Objects

In earlier posts on this blog, I worked with the idea of building nature shrines and sacred spaces of all kinds.  One of the things I often stressed as part of that work was not bringing things into those spaces that might be harmful or damaging to the land.  So I suggested natural things, things like shells, stones, wood, bones–things that you gather yourself, from the land, and allow to return to the land.  Or I suggested things that would easily return to the land, like wood burned object, hand-dyed natural fibers, etc. These will break down quickly due to the elements, but that’s exactly the point.

 

Many earth spirit statues

As I have talked about over the last few weeks, Cob is a natural building material made of clay, sand, and straw.  When you make something from Cob, it’s not fired.  It will not hold up to water. It will break down in the snow, wind, rain, and ice. Why, then, would you make statues out of cob if you know they will break down? First, because there is a magic in impermanence, magic in the making.  When you know something is only going to be a certain way only for a short period of time, it holds additional value.  For example, when my strawberry patch starts to produce the best-tasting strawberries, I know there is a short window, maybe 2 weeks, where I get to enjoy them fresh from the plant.  The rest of the year, I might enjoy preserves, but never that fresh succulent strawberry right from the vine.  Sacred objects can be like that too–an object you carefully construct, with the full knowledge that it will be broken down, creates a different kind of relationship. A sacred relationship based on the immediate moment. Creating these statues asks you to be in a place for this moment in time, to simply be present, making these, working with the cob between your hands. Letting the natural objects find their own shape and in their own time.  And not rushing it.   For there is much magic in the making.

 

There is magic in the making, and there is magic in the placing. An earthen spirit statue’s goal is to return gracefully to the land.  If you want, you can work slow magic with these, on nature’s time and at nature’s pace, as part of this work.  Almost all of my earthen spirit statues are used for the purposes of land healing.  As I shape them, I speak my healing words into them, I work healing energies through my fingertips. I sing, I chant, I smile, I laugh. I put the energy of life and light into my statues. And maybe when they are done, I put some more into them ritually, adding the powers of the elements and the sacred animals of the druid tradition.  Then, they become like little healing shrines all to themselves.  Carefully wrap one and put it in your backpack while you are on a hike, leaving it in the nook of a tree.  Place one on a stone in a stream, knowing the floods will carry it away.  Bury one in a snowdrift in a logged forest to offer peace to the survivors.  Offer one to your local lady of the lake.  Place one in your garden to nurture your plants to grow, letting it become soil you will plant in.

Gathering Materials and Decorations

There are two parts to an earthen spirit statue.  Natural items, such as feathers, leaves, sticks, stones, nuts, roots, seeds, and more are one of those parts. Take a small basket into the woods, beach, bog, desert or whatever is near you.  Walk intentionally and slowly, letting small bits of nature speak to you.  If they call out, pick them up, and leave an offering in thanks.  Once you have a good selection to work with, its time to make your cob!

 

Making Cob

And so, let us put our feet and hands into the earth and make our cob! For an introduction to our delightful material, you should look at the introduction to cob construction here, and how to make cob here. I will also offer basic instructions here, as they differ slightly from the instructions on my introduction to cob page. In a nutshell, cob is a combination of clay, sand, and straw.  This combination, in the right amount (1 part clay/silt to 2 parts sand) makes a perfect material for building earthen spirit statues.

To make your cob:

  • Dig down to the subsoil (see here for more details).  Fill up part of a wheelbarrow (1/2 or so).  Screen it, removing any rocks, sticks, or other debris.  The goal is to have just clay, sand, and straw.
  • Put your material on a tarp.  Make a well in the center of the soil, and then, add water.  Mix with your feet, putting your prayers, energy, and love into that material.  Dance with the spirits as you dance on your cob.  Take a side of your tarp and flip the cob, adding more water to make a good firm dough consistency.
  • If you want extra strength, you can add a bit of fine straw.  To add straw, take your scissors and carefully cut the straw up into 1/2 in pieces or less.  then sprinkle it through, working it in with your feet.
  • Pick up some of your cob.  It should hold its shape well and you should be able to work it.  Add more soil if its too wet and more water if it’s too dry and crumbly.
  • The goal is a nice firm but doughy texture that will hold its shape and that you can form.

 

Goose blessing of my cob

Make Your Statues

Make your statues however you see fit.  the easiest way is to create a cylinder by rolling the cob in your hands or on a solid surface. Then, find the natural objects you want to include.  Press them into the cob, shaping it as you go.  Stick some sticks coming out of it, shells, or dried turkey tail mushrooms (or similar small polypore mushroom). Let the objects speak to you, and let the clay speak to you. Make no thought if it is “good” or “right”; refrain from any value judgments. Your goal is to channel the spirits of nature, and they are not concerned with the physical vessel you are creating.  Don’t fuss over it.  Let it be complete, and make another.  And another, and another, until you feel you are done.  As you make, laugh. Get muddy. Sing to the statues, drum.  Call for the sacred powers of nature who might aid you.  Put happy, healing, and light energy into your work.  Let go.

 

Bless your statues

If you feel the need, you can do an additional blessing for your statues.  Draw upon the power of earth, air, fire, and water, and give a blessing to them–smudge them with incense, drip some beeswax on them or hold them to the flame.  Give them some water drips, smear them with soil.

 

More earth spirit statues!

Place your statues

Find a home for your statues in the nooks and crannies of the landscape.  They want to travel, go somewhere, send their healing energy out as they begin to break down. Put them in unconventional places.  Put the in places in need of light and healing.  Put them on nature shrines.  Put them in your druid’s anchor spot. Visit them and watch them break down, or leave them never to return. You can put one on your altar for a while, but make an agreement between the two of you how long it will be there so that you can return it at the right time (these energies are meant to move between you and the land freely). There is no right or wrong path, just you, the spirits of nature, and how spirit moves through you.