Introduction: MINI WOOD-FIRED PIZZA EARTH OVEN!
Grand Prize in the
Fire Challenge 2017
Wood-fired pizza! Fresh baked bread! Roasted chicken and vegetables! Pies! Soups! Stews! Slightly charred oven mitts! That awesome smoky smell to your clothes! Sound good? You can have all this in your very own backyard, and it can be built in a few days (mostly waiting time) with materials that are very easily sourced, possibly all from your own backyard.
SAFETY: Please use the normal precautions when working with any tools, and especially after you build the oven and start lighting fires. Fire is hot. Make sure you aren't near anything that is a fire hazard, etc.
The short story: This instructable will show you how to build your very own MINI earth oven so you can enjoy cooking and baking small items in your own backyard.
Also known as a cob oven, clay oven, mud oven, or horno (and more!), a wood fire is burned inside of the earth oven, removed after it is down to coals, and all that precious heat from the fire is retained in the clay walls and in your brick hearth, slowly radiating back out into the oven, cooking/baking your food. The temperatures start around 500-600 degrees F, and slowly come down over a long period of time, usually around 24-36 hours in total. It is during this time that you can cook/bake many different foods, starting with higher-temperature foods like pizza and bread, and ending with lower-temperature cooked foods like stews or baked goods. Even when your oven is down to 200 degrees F, it's nice to put some wood in the oven to help further dry it out for your next firing.
The longer story: About 7 years ago, I built a full size earth oven (22.5" cooking floor diameter) that still stands today. I was inspired by and took instruction from Kiko Denzer's book 'Build Your Own Earth Oven'. I built it all on my own over a period of 1-2 weeks with all locally-sourced materials and we've enjoyed countless evenings full of wood-fired pizza, fresh bread with a delicious golden crust and chewy interior, free-form blueberry pies, roasted chicken, roasted veggies, and they all come with a certain earthy scent that is almost sweet, it's difficult to describe, but you know it when you taste it and it's FANTASTIC! As a bonus, after cooking, it's so nice to lean back onto the outside curve of the hot oven and get a hot rock massage with the heat radiating out through your back. :)
I have two young children who love great food, and they both have a certain fascination with watching their dad (me!) fire up our earth oven, tending the fire, pulling hot coals out (yes,they are safely at a distance), putting the door on and letting the oven rest for 20 minutes, then popping in a pizza and only a short TWO MINUTES later seeing it come out of the oven fully cooked, cheese bubbling and golden brown!
The full size oven takes 2 hours of fire to get up to pizza-cooking temperatures. From the time I light the fire to the time lunch or dinner gets on the table is always right around 3 hours. Kids can get impatient, and it also seems like a lot of time, energy, and resources to fire up the big oven if we just want to cook or bake something small.
Voila! Our MINI-earth oven idea was born, as I remembered that in Kiko's book he does feature a 'muffin oven'. It's a very small earth oven built around a few bricks, but has no insulation whatsoever, and as a result, loses heat quickly. I decided to build this 'muffin oven', but add in the features of our bigger oven which includes a nice-looking base, a layer of insulation, a second layer of "mud", and a finish/plaster layer.
My kids and I will cook mini pizzas, muffins and cupcakes (full size), small breads, mini pies, and more! It won't take nearly as much time to fire it up and heat it, and it will retain heat for enough time to cook a few batches.
Get your kids to help you build and cook in it! Get your friends to come over and pitch in! You can absolutely build this yourself but having help is better (and more fun!). My kids and I are very close, and doing this project together bonded us even closer in a whole new way, one I could never imagine.
Step 1: Gather Your Materials and Tools
First, I highly recommend purchasing or borrowing from your local library a copy of Kiko Denzer's book 'Build Your Own Earth Oven'. It is very comprehensive (yet simple!) and covers every facet of building an oven with earth in such wonderful detail, especially if you plan on building a full-size oven. It also instructs on how to make your own sourdough bread! Bonus! The book can be purchased through his publisher here: http://www.handprintpress.com/bookstore/cob-oven-...
Having said that, off we go..........
- Bedding (essentially pine shavings, such as for pet hamsters or chickens)
- Small bottles (vanilla extract size, or small essential oil bottles)
- Newspaper or big leaves
- Wood (for oven door)
- Measuring tape
- Yogurt lid (could be sour cream, butter, or any similar type of plastic lid)
- Old spoon or spatula
- Clay - Finding clay may be the toughest part. Dig down into your soil about a FOOT down or more. That's where clay is. It's not the growing soil in the top 6 inches. Below that is usually silt. Clay almost has a "shine" to it. Where I live, we have so many rocks and boulders to dig through that it isn't worth trying to get down to the clay. Luckily, we live in the mountains and I found a few nice veins of clay during a rainstorm on my hike. That was the good news. The bad news is that I had to carry all that clay back to my car. I made many, MANY trips, digging up the clay and putting it into buckets and backpacks. From all the research I've done on other people building these ovens, most have clay in their own backyards, or close by on a construction site or where road construction is being done. Other places you might find it are at old quarries, riverbanks, ponds, or ask a friendly neighbor if they have clay on their land that you can have. If after all that you can't find any, you can buy pure "fireclay" which comes dry and powdered from your local building supplier.
- Sand - you want coarse sand, not beach sand.
- Straw - not hay.
- Rocks - As I wrote, we have an abundance of rocks so I used that as the base for this oven. For our large oven, we used broken up pieces of driveway that someone was throwing away. You can use whatever you'd like: bricks, rocks, old concrete, etc. Since this is a very small oven, I went with rocks. As Forrest Gump said, "Sometimes I guess there just aren't enough rocks."....... unless you're in my backyard.
- Firebrick - I've heard of using regular brick, but to be safe, choose firebrick. It's made specifically for use in fireplaces and stoves. You can get them from most suppliers of masonry materials. I bought mine here:
- Tarp - just a standard blue or green 6' x 8' tarp. You'll mix your "mud" on this using your feet!
- Small bottles - if you don't have any, you can use garden perlite from your local gardening center. This works fine. I like using the bottles that are just sitting in our pantry cabinet. They finally have a use.
Step 2: Foundation/base
Find your spot where you want your mini earth oven to be. It's small so it can fit pretty much anywhere. I put ours on the wide ledge of a wall.
I had a large 16" x 16" paving stone that wasn't being used so I put that on the wall, supporting it with another paving stone underneath it (see picture).
Your foundation has to support the weight of the oven, protect against ground moisture, be rigid and strong, and at the height you want it. For obvious reasons, don't use a plastic foundation, or even a wood foundation. You're working with fire after it's built and heat can melt or burn these materials.
After deciding on your foundation, put down a thin layer of sand. This helps stabilize your first layer of rock. Start laying down your first ring of rock or other chosen material until you have a full circle. With rocks, you have to play with the different shapes and sizes. I tried to use mostly flat rocks but that wasn't always possible, so you have to 'puzzle' it together until it is sturdy.
Then lay your next ring of rocks (or chosen material) "one over two". Each rock in your second ring should not be right on top of another rock. It should be on top of TWO rocks. This helps stabilize your base as you build it up. Think of a brick wall and how each row is laid on top of each other. I've included a photo of a rock wall to give you an idea.
You can build up 2 or 3 or 4 rows of rock, your choice. I did 3. Once done, fill it with your gravel (this insures that water won't wick up into the oven) up to about 3-4 inches below the top of your rock foundation/base.
Step 3: Make Rings to Hold the Subfloor Insulation
After building your foundation and filling it with gravel, it's time to make a ring that will hold the insulation that makes up your sub floor (under your firebricks). You can use more rocks OR get down and dirty and start making some "mud". This earth oven is made of something referred to as "cob". Cob is the mixture of clay, sand, water, and straw.
Take your clay, and if it's dry, soak it overnight, and it will become soft. Fill a bucket half full of water, add dry clay to it until it's full, and wait until it's soft. Pour off any excess water before using it.
TIP: Since you'll be mixing this with your feet, you'll water to make sure the clay is free from rocks and pebbles. There might even be nails or glass. TRUST ME, IT HURTS IF YOU STEP ON ONE. You can screen your clay through a wooden frame lined with heavy wire cloth (hardware cloth), usually 1/4" or 1/2" is enough to screen out the pebbles and rocks. If you want to skip this step, I recommend mixing up the cob while wearing old shoes/boots. Save your feet!
After getting your clay ready, it's time to lay out your tarp on flat ground. Clear the ground as best you can of pebbles and stones. Even if they aren't in your clay, you'll still feel them on your feet if they are under your tarp.
Here is the basic recipe for making cob:
- One part clay
- Two to four parts coarse or sharp sand
You can skip the straw at this point if you want, but you'll be adding it later for the outer part of the oven. I saved a step and just mixed the straw in too. It won't hurt a bit and actually makes everything that much stronger.
For this project, I used ONE 5-gallon bucket of clay, TWO 5-gallon buckets of sand, about TWO-THIRDS of a 5-gallon bucket of straw, and enough water to mix it together without it being too wet or too dry. More on that in a bit.
Back to your tarp!
Pour your sand in a circle in the center of the tarp, like a donut. Put your clay in the middle, add a little water if you need to, and start a'steppin'! Get your feet in there, pull some sand into the clay, step on it, twist in it, do your 'cob dance'. You'll quickly get a feel as to whether you need more water or not. If you put in too much, not to worry, you can always let the mixture dry out a bit over the course of a day or two. This is where I got my kids to join in, and we got all nice and muddy, laughing, playing, singing, and it helps get their energy out! Keep working all the sand into the clay. At times, you can pull the sides of the tarp towards yourself which helps pull some of the mud over onto itself. Keep it all on the tarp! Then start stepping on it again. You want a nice homogeneous mix. It's easier to do this first before adding the straw. Once you have a nice mix, put in your straw and start your footwork again until the straw is nicely mixed in. There you have it........COB!!
This is what your earth oven is made of!
Grab a handful of your mixture and start kneading it with your hands. Squeeze it and squish it 20-30 times. Make a firm ball with it, and test it. How? Drop it onto the ground. If it crumbles, it either needs more mixing, more water, or more clay. If it's 'splooshes' onto the ground, it's too wet. If the ball maintains most of its shape, flattening only on the bottom of the ball, it's just right, Goldilocks!
Once you have the right mix, start making MANY balls. You will form a ring of cob on top of your foundation rocks. (see pictures) You will want to make the ring high enough to hold your insulation mix (next step) and your bottles (tipped on their side).
You can also use some of the cob mixture as mortar to secure any wobbly rocks in your foundation.
Step 4: Insulating the Floor of the Oven
Cooking and baking require heat, oh precious heat, but if we lose that heat, your culinary treats won't turn out well. How do we preserve that heat? INSULATION!
Before building the actual oven, we will want to insulate below the floor of the oven to help keep all the precious heat from being sucked out of the hot firebricks down into the cool gravel, rocks, and foundation below. This is where this project differs from the "muffin oven" listed in Kiko's book. That one doesn't have any insulation, and as a result, heat is lost quickly.
We will clay, water, bedding material (pine shavings), and little glass bottles.
Mix together some clay and water in a bucket or other vessel until it becomes a heavy cream consistency. This is called 'clay slip'. If you have dry clay, break it up until it is the texture of coarse gravel, put it into a bucket that is 1/3 full of water. Pour off any excess water after putting the clay in. Let it soak overnight. The next day, stir and stir and you should have a nice heavy cream like consistency ............. clay slip!
Mix handfuls of bedding with just enough clay slip to make a firm dough. You should be able to pack the 'dough' into a ball. If you use too much clay slip it will drip. If you use too little clay slip, it will crumble.
Put a 1" layer of your insulation mixture on top of your gravel. Then lay your bottles down and nestle them gently into the insulation mixture (you are not burying them). Leave a 1/2"-1" gap in between bottles. Then fill in those gaps and cover the bottles with more insulation mix. You should just be able to see the top side of the bottles (see pictures).
You can either let that dry, or continue. The next insulation step is to put a layer of cob (EARTH/MUD/CLAY MIX) on top of the insulation mix you just covered the bottles with. Since you've already made your cob, it's time to make more cob balls and make an earth floor with it. (see pictures) Make plenty of balls and start putting them on top of the bottle/insulation mix. The cob should be soft enough to work all the balls together so it ends up as one uniform floor piece. (see the pictures)
You can let this dry, or continue. It's a good time for a little break, even a day or two if you want. The more each layer dries out, the quicker you can fire up the oven and actually use it.
Step 5: The Hearth!
You're getting closer! Your oven is about to really start to take shape, so keep at it!
It's time to lay down your firebrick. This is what you'll be cooking on so we want to make sure your bricks are even, flat, and clean (if using used bricks). Your cob sub floor should be nice and flat, and quite firm, well on its way to being dry. Smooth out a very shallow layer of sand on the sub floor and do a practice run of where you'll lay your bricks. Take a look at your oven so far from the top down and try to center your bricks. You'll also want to see if the tongue is where you want it (this is the part of the bricks that will be outside of your oven door. (see picture)
Once you're satisfied, mark either a center point or even a corner where you will lay your bricks, remove the bricks and then carefully reset the first one back to your marked point. Take your next brick and starting about an inch above the surface of your first brick, gently "kiss" the long side of the brick you're holding and slide it down the long side of the first brick that is already on the oven floor. It should fit nice and snug against the first brick with no gaps. Take the handle end of a hammeror similar tool and tap tap tap the brick down firm. Once the brick is set, don't touch it! You don't want sand in between the bricks. I ended up with a slight gap in between my two front bricks (sort of like David Letterman) because of the way the bricks were cut, and I ended up filling the gap with some cob material. If yours don't sit flush, take them off and redo them. It's quick and easy and in the long run, very worth it.
Once done, take a string and tie it to a pencil close to the writing side, not the eraser. You will be holding the other end of the string down at the center of your SUB FLOOR and drawing a perfect circle on the bricks so that the sides of the circle "kiss" the edges of the bricks. (see picture)
This is where you will be building your sand mound (next step) and eventually will be your oven cavity where you'll build your fire and cook your fine food!
Step 6: Make the Interior of Your Oven
Now it gets super fun! It's time to make the inside of your oven. How? You build a mound out of sand that will be built upon with your cob material, and later remove the sand leaving a beautifully curvy dome inside.
This part is critical: You'll want to have enough time to make your sand dome AND cover it with the first layer of cob material all in one go. If you don't finish the layer of cob and have to start on it again at a later time, you end up with a 'cold joint' that makes for easy cracking and damage when you light up your oven. With a small oven like this, it's pretty easy to get it done in a few hours (if by yourself). When I made my large oven, I worked from 8am until 1am to get it done (again, by myself) and it was NOT fun. I was almost crying by the end. (So make a note that if you decide to make a larger oven, get your family and/or friends to help!)
Get your sand and get it damp, like you're at the beach building a sandcastle. If it's too wet, it will slump. Too dry, it'll fall apart on itself. Just like coloring back in kindergarten, stay inside the lines of your circle! Start to build up until you have a dome shape. The sides of your dome should go straight up vertically from the bricks for about 2-3 inches before it starts to arc inward. Kiko's book put it best: "Imagine a hemisphere sitting on a 2-3 inch disk". (see picture for an example.
Keep the edge of your circle very defined (stay inside the lines!). I built my sand dome up to a height of 9". Hold a straight stick across the top of the dome and measure down to the bricks.
Your dome should be even, solid, and hard-packed. To make it easy to remove the sand later, cover your dome with wet newspaper, either in a big sheet, or think strips if the big sheet is tough to work with. Smooth the paper down flat so any edges won't get caught in your cob and make a crack later. (see pics)
NO REST YET!
It's time to start building your cob around your dome. This is it! You're about to make your oven!
Take handfuls of your cob, make them into balls (squeezing and kneading) and start pressing handfuls of it around the base of your sand dome. This is what will be holding your bricks in place AND will form the shell of your oven.
IMPORTANT: Press the cob mixture down onto itself and NOT IN towards the sand dome. If you do, it will damage your sand dome and that will be that. Always work each next handful of cob onto itself, pressing down, using one hand as a guide to keep the thickness even, and the other hand to press down.
Keep going until you've covered the entire sand dome. Look at it. Are there flat spots? Low spots? Hills and valleys? You can use a small flat board to blend all the irregular spots together until it's one nice looking smooth shape, sort of like an egg. (I neglected to do this, and while I was able to fix it later, it wasn't easy, so do it right the first time).
Once done, take that same board (a 2 x 4 works great) and whack the clay dome firmly to help consolidate all of the material. It should sound solid. If it's slumping or sticks to your board, it's too wet. Let it dry a bit a come back later to try again.
CONGRATULATIONS! The hardest part (in my opinion) is over! Well done! Go rest!
Step 7: Knock Knock! Who's There? Nobody, Because You Don't Have a Door.
Cool, your oven has dried out a bit, hopefully not too much where it's hard. It's time to cut a doorway and remove your sand. Exciting!
Ok, so for a normal size oven, the door height should ALWAYS be 63% of the INTERIOR height (the height of your sand dome). So for mine with a sand dome height of 9", the height of my doorway should be 9 x .63 which equals 5.67". The width is typically half of your oven floor width (which in this case is the width of one full brick or 9"), so my door width should be 4.5".
Kiko recommended in his book to make the doorway height about 2/3 as high as the oven (67%) and nearly as wide as the brick floor. Based on my 9" dome height, this would make the door height at 6" and the width of the door at 9" (my brick floor width). I didn't listen to him and made the door height 5" and the door width also 5". It was my instinct that I would lose too much heat with a wider door.
I drew a rough door shape with a knife, or you can use the edge of a spoon or a stick. Start cutting out your door and make sure you cut down at an angle into the cob material, Pretend you're cutting the top off a pumpkin for Halloween. If you cut straight in, the door will fall into the oven. See the angle of my knife in the picture? That's what you want. This makes the INSIDE of the cut lower than the OUTSIDE of the cut.
IMPORTANT: Your door height should be measured from the LOW POINT (the inside cut).
Once done, pull your cut piece off and what do you see? Your newspaper and sand! Hello old friends!
I measured the door height from the inside cut and was too low, so I cut some more to make the height just the way I wanted it. You can see the difference between the 3rd and 4th pictures.
Step 8: Remove Your Sand and Say Hello to Your Oven Up Close! Echo! Echo!
Take your spoon or just your hand and start scooping out sand. What was all that newspaper for? So you know when you've reached the inside of your EARTH OVEN. You don't want to scrape through the newspaper and gouge your beautifully smooth interior. I used a spoon at the beginning near the middle of the oven and even let my kids have a go at it (see videos), but always switch to using my hands as I reach the edges so I can feel for the newspaper. It's very satisfying to pull a piece of the newspaper off, revealing the inside of your dome. I used a flashlight to see inside as I get near the end so I can really tell what I'm doing. It's dark in there! If you have some rough or loose spots inside (I sure did!), don't worry. Take the back of a spoon and smooth, polish, and compact it. It's a good time to take a break, and also fun to say hello to your oven interior right up at the mouth of your doorway. The echo is quite pleasing! (or I'm very easily amused)
You know what? You have a basic oven! Once the oven completely dries out, you can start baking and cooking.
It won't hold heat for very long, but you could use it.
This is where Kiko's book stopped for the 'muffin oven' but I continued with insulation. It's up to you. :)
I also built an "arch" at the front of my doorway using long pieces of cob that had longer pieces of straw mixed in, but is not necessary to use or build the oven. It's just for aesthetics BUT is an EXCELLENT way to get a tight-fitting door.
Yes, you cut the doorway, but you still need an actual door! You could use what you cut out but it doesn't always fit well, nor does it last very long if it's crumbling. Take a piece of paper and trace over the door opening, put the paper against a piece of wood (I used redwood since it's somewhat impervious to heat) and cut out a door. Smooth out the edges with sandpaper, put some type of handle on the front (I used a plain ol' stick with a couple of nails!), and then put it up against the front of your oven. Do not fret if it doesn't fit, because you're going to use your cob mix to build an arch up and around the doorway and your DOOR. This insures that your door will fit perfectly!
Step 9: More Insulation, But It's Quick!
Ok, you're well-rested and ready to finish this thing off.
Did you run out of clay slip/bedding mixture or did it dry out? Make some more, because you'll be packing a 1" or so layer around the outside of your oven dome. This is pretty quick and fun. Make sure it's not too wet or dry, it should form into a ball. You can definitely press this against the oven at this point (don't push it too hard). Just pack it around and think of all that heat that will be kept inside your oven.
Step 10: Another Outer Layer of Cob, But Thinner!
It's best to let your insulation layer dry somewhat or fully, but it's not a necessity. I didn't let mine dry out, as I wanted to finish this oven fairly quickly, BUT it does mean that it will take the oven longer to fully dry out completely.
Still have some cob mixture left? Great! Make more balls and cover the insulation layer with about a 1/2" or 1" layer. You're almost DONE! Your hands are feeling a little raw, I know, but really, you're in the home stretch. Lotion for your hands awaits, and delicious wood-fired food is right around the corner!
Once fully covered with your final layer of cob, let it fully dry, and you're good to go!
You COULD cover it with a final plaster layer which makes it look all smooth and pretty on the outside, along with helping to protect it from rain, but this baby is fully insulated and ready for cooking!
NOTE: Speaking of rain (or snow I imagine), this is clay and sand. It WILL "melt" if water gets to it. A light drizzle won't harm it but I've been caught in a summertime rainstorm without having covered my big oven, and lost a good chunk of it. The repair is not always easy or doable, so use that tarp again and cover it when inclement weather is expected, or build a roof structure over it.
Step 11: FIRE IT UP AND COOK!
Congratulations! You've arrived and have completed making your very own earth oven! Well done! Now it's time to enjoy the spoils! I won't go into fire-making here, but will offer a few tips:
- Start your fire on the outer part of your brick tongue, and as it builds, slowly push it further back into the center of your oven. This may take a while. And please use a tool or stick or something to push the fire back, not your hands.
- I fired mine up for the first time before EVERYTHING had a chance to dry out and it took close to an hour to get the interior hot enough for the fire to be pushed into it. Be patient. Get to know your fire. More importantly, get to know your oven! This takes time and practice, and is well worth it!
- After getting your fire into the center of your oven, you will need to keep feeding it with small pieces of wood because it's such a small oven. Have your wood ready.
- Once your fire has been burning for a good hour and has burned down to coals (you've decided to stop feeding it wood), you will rake the coals out using some sort of tool like a mini hoe or rake. I used a stick with a curved end and it worked great. Make sure you rake the coals onto something safe. I had a lot of sand underneath the oven which worked great. You can rake it into a bucket or other metal container, just be aware of HOT COALS coming out of the oven towards you.
- You'll still have ash on the oven floor. You'll want to have a stick with a wringed out (wrung?) cotton rag attached to the end of it, perhaps with a nail through it. Essentially you want something like a mini-mop to clean off the oven floor. This takes just a few sweeps of the oven floor.
- Place your oven door on and let the oven "soak" for a few minutes. This will help even out the temperature of your oven floor. For such a small floor, it may not even be necessary.
- I purchased a laser temperature gun to use with my large oven, and came up with a temperature of around 250 degrees F, lower than I would have liked, BUT, the oven is definitely still wet in parts, so I'll try again in a few days after letting it dry out more.
- You can try cooking muffins, cupcakes, small breads, pies, pizzas and more! Experiment! Learn! And yes, you cook right on the oven floor!!!
BAKE! COOK! EAT! SHARE! After eating, place your hands on the outer part of the oven for a hot stone massage!
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