Today is the most exciting day of your life. You're going to learn How to Build a Pizza Oven!
When last we met, in part 1 of this series, I had built the base and the sand form for my cob oven and lost my funny bone. It's currently buried beneath a layer of pizza fat.
Now it's time to make the actual cob for the pizza oven. The cob is the material of the first layer of the oven. The cob is the layer that will heat up (the thermal mass). The insulating layer, which comes after the cob is what holds the heat in.
As I keep saying, these tutorials are meant to be a reference to how I built my oven. If you want to build your own I highly, high, HIGHLY recommend you buy the book Build Your Own Earth Oven and watch architect Sigi Koko's 4 part video series on How to Build a Cob Oven.
The book will give you accurate measurements for your oven so it will vent properly, and accurate amounts of how much building materials you need for various sized ovens as well as a ridiculous amount of pointers. Sigi's videos will have the book all make sense and give you a great visual reference.
My posts, will give you a good idea of the work involved and the confidence that you can indeed do it yourself.
Also there's a lot of stomping involved so it'll give you great legs. Don't get excited. Those will disappear when the stomping stops and the pizza eating begins.
The materials to make cob.
Clay
Sand
Straw (straw is only used in the insulating layer of cob)
One of the reasons I decided to go with a cob oven for my pizza oven was because the materials are either free or cheap. My town happens to be filled with clay, so I knew all I had to do was dig up my mother's yard to find enough clay to make an oven. Sand, well that's cheap enough and straw goes for around $4 a bale at my local feed store.
If you watch the videos and read the book I recommend they describe perfectly how to see if the clay you've dug up is pure clay, or clay with a certain amount of sand content. Mine, as it turns out, was fairly pure.
The reason you need to know this is because the amount of sand you add to your clay will depend on how much sand the clay already has in it. You're creating ancient cement basically.
The clay and sand (in the required proportions), I believe mine was one part clay to 3 parts sand, are mixed together. Not an easy feat. Or feet. You stomp and jump and turn and toss and jump some more to fully integrate the sand into the clay.
Your mixture needs to be sticky; so enough clay that it will all stick together, but enough sand that once it dries it won't crack apart.
Mixing and testing cob
Is making a cob oven a pain? Yeah. A little bit. Is it fun? You bet. Worth it? DEFINITELY. Here's a quick look at how to mix your cob and test it for the proper consistency
You can see in this next picture that I've placed a layer of newspaper over the sand dome. This is so when I go to dig the sand out to crate the interior of the oven, I'll know when to stop digging. Once I hit newspaper I know I've made it to the cob layer.
Creating the outside of the oven (the cob layer) involves grabbing a handful of the mixture, plopping it down and smashing it with your fist to make it nice and tight. This layer needs to be around 4" thick. Just keep plopping and smashing. Plop and smash, plop and smash.
You'll know you're doing a good job when you look like you joined Fight Club.
Don't worry about it. Suck it up. Show those knuckles off. You're knocking out a pizza oven, Sugar Ray.
Once the cob layer is done, you need to let it dry for a couple of days. Just enough so it won't collapse when you start your next step.
Which is cutting out the door of your pizza oven.
The door needs to be specific measurements (again explained in the book) in relation to the size of the oven in order for the pizza oven to vent properly. If your proportions are right the smoke from the fire inside the oven will roll up to the top of the pizza oven, then roll right out the top of the door.
The smaller your oven, the smaller your door needs to be, the smaller the pizza you'll be able to fit into it. Bigger oven means bigger door which means bigger pizzas.
My oven's door will barely fit a 12" pizza peel. I can fit 2 pizzas in it at a time.
Once your door is dug out you'll discover your original sand form ...
Which you can now dig out. Once you dig that out, you'll have something that actually looks like a genuine wood burning oven and you'll be very, VERY excited. So excited in fact that you'll spend a lot of time running, squealing and shaking.
It's a pizza oven. It's a bread oven. It's the focal point of your backyard, neighbourhood, TOWN, p r o v i n c e, COUNTRY, P L A N E T!
And you built it. With your own bare hands.
Let's move onto the final step of How to Build a Cob Oven, Step 3!
Hi Karen,
I’ve read this post a million times as I dream of building a pizza oven and do not want to spend thousands on something I don’t even know how to cook in yet!!
I had a wondered if living in a wet and also snowy climate do you have to cover your oven from these elements? If not, without that protection has it held up okay?
Can you paint the lime layer once it’s finished.
Also I am curious as to why there is no chimney?
Your projects always turn out so beautiful. Thanks for sharing with us.
Chelsea
Hi Chelsea. The only time I cover up the pizza oven is just before winter. You don't want it to get rained on, then have the rain freeze because any rain that gets into the small outer cracks of the oven will expand, cracking them more doing a lot of damage. There's no chimney because it's designed in a way (you have to be very specific in your measurements) that it doesn't require one. A draft is created that pulls the air and smoke out through the top of the oven door. As far as painting the lime plaster, you can do it, I'm just not sure how. Good luck! ~ karen!
I'm a potter by hobby, so this project really speaks to me! Couple of things - couldn't you use a paddle of some sort, like a 1x4, instead of your knuckles? Also, you can buy moist clay, but it is certainly a lot cheaper to dig your own, especially considering the quantity this must take. I read the whole thing but I don't remember - did you say about how many pounds of clay you used all told?
Hi Dee! You probably could use some sort of tool, but I find I do my best work when I'm using my hands as a tool, lol. Just wearing some good, fleece lined gloves would probably work but they'd also become heavy with clay. I actually have no idea how much clay I used. Around 3 or 4, 5 litre pails if I remember correctly. The amount you use also depends on the size of oven you're going to make. If you live in an area that has diggable clay then that's the easiest, cheapest and best way to go because it already has a certain amount of sand mixed in with it. You just have to figure out how much through a water shake test and add as much more sand as you need. ~ karen!
I love your cob oven, actually I am in the process of building mine, myself. I love the feel of earth. Mine is about 30 inches at the base, how high/ should the door be. One more question as I laid the bottles at the base I covered it with clay and sand but it was not too wet, will that be alright. Thanks and congrats once more .
Hi Zeenat. Congratulations on building your oven! It sounds like you may need the book I recommended though. "Build your own earth oven". It answers all of the questions that people have while building a cob oven. (I had about a billion questions during the process) Like how high your door should be for example. It's all based on mathematical equations and proportions that would be in the book. And if you don't do things properly your pizza oven might not vent properly, or even worse, might collapse, which would be horrible after all your hard work. I can't answer your questions (because I don't know the answers for sure) but I can tell you the book will answer all the questions that will pop up. ~ karen!
Brilliant! In my continuing mesmerizing research, based on what I learned about horno ovens at the Red Willow Reservation, a horno oven and cob oven are basically constructed in the same manner except they call the material of clay, sand and straw adobe.
Ok....I know I'm late in response....been gone.....and ...I KNOW I'm supposed to comment on your pizza oven and all and YES it is awesome and you are a stud! Of course I have acknowledged this before! LOL....but seriously you look GREAT! In great shape! LOL THIS is what I noticed! LOLOL You sexy thing!!!
I seriously did not know that you could levitate..I am really impressed now..
But, wait...where does the hay come in? Didn't you say cob was clay, sand, and hay? I saw you mixing the clay and sand, but did I miss the part where you add hay?
I think the straw is only used in the insulation layer that we will learn about tomorrow.
Yes ma'am! ~ karen
So this is how you fed yourself while the kitchen reno was in progress.
I am so pleased to see this, I have been dreaming of a pizza oven but the kits are quite hideous. Seriously I thought cob was made with corn cobs...will you tell us how many hours you put into this endeavor?
Alright Karen, you've inspired me. Or rather, I now have "she did it so I can do it too "syndrome...I've been toying with the idea of using cob to create walls and/or planting beds in my backyard but always chickened out. Really, it would make sense since I need to dig out a lot to level it which will give me all the clay I need. It just seemed too hard or too much work to be possible. Now you've gone and made it look possible. Of course, now I also have my heart set on building a pizza oven while I'm at it. This will all have to be a project for next year though, because right now I have a very clingy newborn and I don't think digging in the heat while wearing the furnace that is my giant baby (seriously the kid is 14 lbs. 10 oz. and not even 3 months old yet) will be very possible. Now I will go back to obsessively reading about cob a la 2 summers ago and make a real plan. Stop me before I build a cob play house for the baby too! My husband is really not going to be happy about this.
geeking out a little bit about the clay...er cob. I guess we'll learn more tomorrow, but I'm super impressed that the structure was able to support itself after just 2 days of drying! Curious about how you prevented collapse, and now a year later...cracking. Did you have to let all the moisture leave the cob before putting on the insulating layer and the plaster? Maybe I should just read the freaking book
You kick serious butt!
As a fellow pizza lover, I was inspired to make this for you. ;)
My husband has been in the process of "making" a pizza oven (we call them hornos here in New Mexico) for oh… about 2 1/2 years now. We have our pile of bottles for insulation and he has the cinderblocks all piled up to create the base and he keeps rearranging them according to different ideas of desired height, design, etc. I just really wish he would switch to legos instead- same activity but smaller, lighter and neater. Would it be wrong of me to finish his oven while he's out of town for a week?
OMG! This is fabulous! You are such an inspiration!!
I watched the YouTube videos and they were great. Very detailed. I wish you had filmed the part where you mix the straw with your feet. That would have been strong competition for Lucille Ball's infamous grape-stamping scene.
I'm noticing the plants on the wall in back of you. I don't remember that lesson.
Just ordered the book. Love that oven, going to build my own. Of course I’m 5 years late reading this blog. Ps.... you still have your funny bone .
I still can't get over the fact that you kept this secret from us a whole year! A YEAR, Karen! How could you do this for a year? We come here and live imaginary life with you, thinking we like a good neighbor, we know everything about you, and know what underwear you wearing (or not wearing) today and then this? Secrets? Secrets = lies.
Now reading your post I think I might reconsider my husbands idea to built pizza oven. I always thought they look dumb, like a bald head sticking out in the yard. And I think it's one of those things that I might use one time and then back to our BBQ grill. Kind of like cheese press that I want to buy so bad lol. Your looks very authentic and Artisan and you make it sound like it was a weekend project. lol
Awesome and dare I say looks easier to do than I thought!