Introduction: Building a WFO (wood Fired Oven)

Picture of Building a WFO (wood Fired Oven)

In the spirit of off the gridness and in an effort to be more self-sufficient, my wife and I recently tackled a new project at home.  We built a wood-fired oven, or WFO, if you prefer. 

An outdoor wood-fired oven gives us another option for many kinds of cooking.  It also provides a great accompaniment to the barbecue.  The WFO is a lot of fun to built and use.  It provides a lot of feel good factor for having done it ourselves with little money.  Of course, it also makes great tasting food.

We over-researched the subject by reading several books and by searching online before finally building it.  We need not have prepped so much.  Two of the most helpful resources were http://www.traditionaloven.com and the book “Build Your Own Earth Oven, 3rd Edition: A Low-Cost Wood-Fired Mud Oven; Simple Sourdough Bread; Perfect Loaves” by Kiko Denzer.


Materials list and cost:

I used:

less than 1.5 yards of 5/8 minus for the entire project – about $40.

"Urbanite" and large rocks - free.

Concrete block – free from freecycle.

Sand – free from river.

Coarse Sawdust – free from a local lumber mill.

Perlite – about $30 from the hardware store.

Clay – $150.  (It could have been free with more elbow grease)

Material for the door – free from around the property.

 

Total cost:        under $200.


Step 1: Pick Your Type of WFO

Type:  We discovered that there are several types of WFO’s.  Which is best depends on who is writing the article.  Our primary concerns were the difficulty of the project, the cost of the project, and the look of the project.  A $15,000 brick and marble WFO would look silly sitting next to our farmhouse, would be way beyond our budget, and might be beyond our construction ability.  We decided on an adobe, cob, or clay oven.  They exact material seems to be interchangeable.  Since we are part-time potters, we happened to have a sixty-gallon garbage can full of left over clay from the past couple of years.  We decided to use what we had

Step 2: Location, Location

Location:   One of the most important and also most difficult parts of this project was picking a location.  The WFO requires a location that places its back to the wind.  Ideally, it should be out of the elements.  It also needs to be accessible enough to be useable.  We finally decided to locate our WFO off the end of our screened front porch, facing away from the wind.  This would require rebuilding that end of the porch to allow for a screen door, building a shed roof for protection from our very frequent rain, and leveling the ground in that area.

Step 3: Size Matters:


Size:   We wanted something big enough to bake a small pizza, a small roast, or turkey, or a couple of loaves of bread at the same time.  We wanted it a bit on the small side so that it would use less firewood and so that it would blend in.  We settled on an inside diameter of 22 inches wide by 16 inches high.

Step 4: Getting to Work: the Foundation

Picture of Getting to Work: the Foundation

The Foundation:  I started the project by locating the oven far enough away from the porch for safety yet close enough for convenience.  I dug a square hole 54” wide and about 6” below the frost line and leveled the hole.  Into this square hole I packed level about 4” of 5/8” minus gravel. 

Step 5: Building Up the Base:

Picture of Building Up the Base:


Upon this foundation I laid a square of the 8”x8”x16” concrete building blocks, three blocks to a side.

Step 6: Completing the Foundation:

Picture of Completing the Foundation:


I stagger stacked five more layers of building block.  After each layer of block, I filled the square with “urbanite” and large rock, filled all of the spaces and covered the rubble with 5/8” minus, and compacted it all with a length of 4”x4”.  I did not fill the last layer of block so that the insulation layer would be deep enough.  I capped the last layer of cmu with the 4”X8”x16” concrete cap. 

Step 7: Adding the Insulation Layer:

Picture of Adding the Insulation Layer:


The resulting 12” void was filled in with an insulation mixture made of sawdust, perlite, and clay slip.  Equal quantities of sawdust and perlite were carefully measured by the shovel-full into a wheelbarrow.  Clay slip, clay mixed with water into a sour cream consistency, was added until all of the particles were coated with clay.  A rough ball made of the insulation mix did not splatter or break apart when dropped from waist height.  This insulation layer was packed and leveled.

Step 8: Fire Brick Layer - the Oven Floor:

Picture of Fire Brick Layer - the Oven Floor:

The Oven Floor:  We purchased 16 medium-density firebricks from the fireplace shop and set them into the insulation layer.  More of the insulation material was used to level the floor of the oven prior to building the oven itself. 

Step 9: Building the Oven:


The Oven:  I used a string with a pencil to draw a 23” diameter circle on the firebricks.  Sand from the nearby river was screened and used to make a sand dome.  We dumped wet sand in a pile on the bricks and painstakingly molded a dome.  It was not as easy as it should have been.  This was the most frustrating part of the project!  Finally, after starting over a few times, we achieved a nice-ish, 16” high, rounded dome.  Several layers of wet newspaper were plastered over the sand so that the clay layer would not stick to the sand.

(sorry, no pics of this annoying step)

Step 10: Building the Oven - the 1st Layer:

Picture of Building the Oven - the 1st Layer:

Our soil is very heavy with thick red clay.  Either it is too wet to work, or is so hard that you need a pick to get it out.  We had originally thought to dig our own clay, mix it with sand and straw, and to use this material for the oven.  However, we decided to cheat a bit bought some very rough clay intended for large structural structures from the pottery supply warehouse.

We packed this clay 4” deep around the sand dome.  Layer by layer we pressed the clay into itself around and over the dome, being careful not to press into the sand dome. 

My wife then used a 2”x4” to not-too-gently smack the clay dome into a proper shape.  The smacking helps consolidate the clay into one cohesive shell.  Just do not smack it too hard or you will end up with a bulge on the opposite side or around the base.  An arched door was drawn onto the front of the inner clay shell.  It was about 66%, or 10.5”, high by 12” wide.

Step 11: Building the Oven - the Insulation Layer:

Picture of Building the Oven - the Insulation Layer:

Over the inner clay dome, we laid up a 4” layer of the same insulation material used for the floor.  The insulation layer stopped about 4” short of where the doorway was going to be cut. 



Being impatient, we cut doorway into the dome.  The doorway was cut with a bevel to keep the door from falling in.

Step 12:

Picture of

The 3rd and final layer of the oven was a 2” layer of clay.  This exterior shell was layer up in the same fashion as the other two layers with great care not to push the clay into the insulation layer.

The exterior clay shell was wrapped over the exposed insulation layer around the door.  This created a continuous clay shell with a 2” reveal around the doorway.

After some drying time the oven was now firm enough to remove the sand.  Using a garden trowel my wife carefully dug out the sand.  When she hit newspaper, she knew that she had reached the inside of the dome.  After the sand was removed, the newspaper was carefully peeled off the inner clay dome.  A smooth piece of rounded wood used for shaping bowls on the potter’s wheel was used to smooth out the rough spots on the inner dome.

Step 13: Finishing the Oven:

Picture of Finishing the Oven:

The exterior shell was paddled and shaped into a smooth cover.  The final layer had to dry a bit before it could be smoothed completely.

My wife threw an onion shaped finial for decoration on the top of the oven.  She then carved various designs into the dome.

A door made from 2x6’s was cut to shape.  1x6’s were cut to go over the face of the door and to extend 1” beyond the door in order to act as a flange to keep the door from falling in.  An extra chunk of tile-backer was cut to shape and screwed onto the inside surface of the door for a heat shield.  A pair of handles left over from a previous project completed the door.

Step 14:

Picture of

Getting it to work:  A small fire was lit inside the oven to slowly dry it out from within.  The sun worked to dry it from without. 

Step 15: Time for Dinner!

Picture of Time for Dinner!

After it was dry (enough), we brought it up to white hot, pulled the coals out, put the door in place, and soaked it for about 15 minutes.  While it was very hot, we cooked up a few small pizzas.  It actually worked!

Since then we have baked bread, pizzas, backed beans, veggies, and bagels in it.  We have learned when to pull the coals so that the food does not taste too smokey.  The oven is a big hit.  Many of those who have seen it want to build their own.

The WFO’s potential and use are obvious.  We have never used “firewood” in this oven.  We have always used sticks, branches, and other left over non-treated wood products for firing the WFO.  Usually about ½ of a five-gallon bucket is all that is needed per firing.

Comments

IamTheMomo (author)2015-03-01

You and your wife are incredible artists. This truly is a work of art, and I salute you both!

jon ball (author)IamTheMomo2015-03-01

You wouldn't think so,looking at it now. The exterior doodads have all popped off. The clay is pitted from the pounding wind driven rain. The flange around the mouth keeps cracking apart and falling off. But, with about ten minutes off clay patching, it still makes great pizza and bread, baked beans, etc. It will come down this summer, probably. Maybe not. Gotta build a new chicken coop, get the duck pen up, repair some of the raised beds,............

Prodromal the professor (author)2014-06-23

What kind of clay did you use? Was it a low fire clay?

Have you had any problems with the clay absorbing moisture out of the air yet?

we used a mix of lowfire 04 up to highfire cone 10. we've had many problems with it. The decorative items have all separated. Large cracks (1/2") have popped up here and there. The mouth has lost most of its structure. However, we just keep slapping clay on it to fill in the cracks and keep on going. Cooked last weekend with it. Got it to 1600F inside, still cool outside, flash cooked the first pizzas, kept cooking the rest of the day. It was still warm the next morning. We had intended to rebuild it this summer, but the misses has been diagnosed with wheat, egg, and diary allergies. so................not sure at this point. I am trying to win the arguement for conversion to a forge - I've a hankering to pound out some sharp n pointy things.

jon ball (author)jon ball2014-06-27

sorry, i meant Dairy ....not diary.

saosport (author)2014-04-09

Does anyone know how one of these would hold up in the Midwest? I live in WI and thought it would be great but I am not sure how it would hold up in winter.

ilhadad (author)2013-07-17

What is clay slip? Where can you get this material?

jon ball (author)ilhadad2014-01-20

Sorry about the delay. Yup, just mix clay with water. Runny or thick, it is up to you.

theegghead (author)2014-01-18

clay slip is just clay mixed with water

Duplo for Daddies (author)2012-01-09

This looks great! I am working on starting a bakery, and have been wondering about doing something like this for some more special breads, in addition to stuff baked in a regular oven. Wood in my area is kind of sparse, so I might take on your challenge of making a gas powered version.
I am wondering (you might have an answer), are these kinds of ovens more energy efficient than modern kitchen ovens or industrial ovens?
I'll let you know if I ever get to making my own one.

surfdude (author)2012-01-02

Great job an nice instructable.

drewgrey (author)2011-05-31

Good job, Did you say half a 5 gallon bucket of wood to bring it to temp. Thats amazing. Mine takes alot more than that. I have a laser thermometer that says that I have an average cooking temp of 750 or so. Do you have a metal peel yet?

jon ball (author)drewgrey2011-05-31

Ya sure. We bought one from our local Grocery Outlet. It was a tad bit wide so I had to shave it up a bit.

Tell me about your laser thermometer. I've not seen one of those. We would like to be able to tell just how hot the oven gets. "white" "red" "orange" works pretty well when temping metal, but not so much for the inside of a dark oven.

Remember that for our heat we burn the wood to coals and then soak the oven with the door on for a couple of hours. That really saturates the base and the oven with heat which is then reflected back into the cooking chamber. Patience is a virtue here. If we have a long day ahead of us we will renew the coals and keep a few pushed to the back of the oven. It does take more wood then. Usually we use scrap fir or cedar to start it going and the heating fire is from maple or alder. We are curious how this would work with charcoal briquettes right out of the bag. I suppose that this could be rigged to use gas as well. Curious.

drewgrey (author)jon ball2011-06-01

We got our laser thermometer from sears but harbor frieght has them cheap also.It gives a reading off whatever its pointed at. We got it for brewing beer but have found it entertaining for other stuff ( like testing my cladding compound for heat retention and insulation).
We start our fire at least 2 hours before showtime and continue burning while we cook. Since we have an interior diameter of 36" there is room for the fire at the back and pizza in front. After every few pizzas we pull the fire to the front to clean the cooking area, or after a cheese and topping malfunction. A great benifit of having a fire while cooking is that the pizza wants to be cooked from both sides at the same time. Perfect crust and slightly tan cheese!

Ricardo Furioso (author)2011-05-31

Lovely work.
I have lots of questions.
Can you please add a photo of your door?
Is there a chimney, or does all the smoke come out the front?
Where does the fresh air come from to feed the fire?
What method do you use to remove fire and ash before cooking?
Thanks.

jon ball (author)Ricardo Furioso2011-05-31

No chimney. All smoke come out of the front. The wood is burned with the door off. When only coals are left, the door is placed. After a period of time (the "soak" period) the door is removed. we bent a piece of metal, attached it to a stick, and use it to scrape out the coals into a steel bucket. A rag wrapped end of another stick is soaked in water and used to "mop" out all (most) of the charcoal.

I am getting ready to post another series of pics. we've torn off the exterior layer, mixed in about 40% more sand, have placed the new exterior layer back on, are letting it cure to the right consistency for wacking (preshaping) then final shaping. We are going to add on an arched entry made of clay which has been fired in the kiln. This will give us a place and the support for a front located chimney.

I'll post pics of the hardware then as well.

jbchurchill (author)2011-05-31

Nice! Very inspiring!

tim_n (author)2011-05-31

You wanted pics, I post pics :)

Mine is more rustic, I've not added the final finishing clay level. The odd rustic look is made by the insulation - that's clay slip mixed with sawdust. Seemed to do the trick anyway - only started getting really hot after we'd been using it about 4hrs. First pic as the pizza was in, 2nd pic as I removed the first ever cooked pizza.

tim_n (author)tim_n2011-05-31

If you want to see my pics you can goto www.waark.com and see the steps I used.

brazell (author)2011-05-26

Great job!!!! It looks beautiful! Can you take a pic of the door?

jon ball (author)brazell2011-05-26

As you can see the door is rough. The next one will fit better. Still, after a year, it works great! All of the screws are short so that they do not go all the way through. The handles stay cool.

DriX (author)jon ball2011-05-27

Your door is made of wood???
Mine is made of 1/2'' iron and bends a little over time because of the extreme heat.

brazell (author)DriX2011-05-27

No, the door has a tile backer, but I did not understand what he meant, so I asked for a picture. You just have to read the whole thing and it is on step 13. See below. Also, I am not trying to be snippy/snarky/sarcastic, hope it doesn't seem that way.

13...."A door made from 2x6’s was cut to shape. 1x6’s were cut to go over the face of the door and to extend 1” beyond the door in order to act as a flange to keep the door from falling in. An extra chunk of tile-backer was cut to shape and screwed onto the inside surface of the door for a heat shield. A pair of handles left over from a previous project completed the door."

DriX (author)brazell2011-05-27

Thanks, english isn't my first language so somethimes i don't understand something (i didn't knew the meaning of "tile-backer").

Now it's clear. But i'm concerned about that door, it might catch on fire.. Mine turns orange-red sometimes..

Here they are quite common, we call them "hornos de barro" ("mud oven").

But we don't make it that way, we use mud mixed with: dry grass, horse/cow poop, glass dust, and other little secret engredients. And it's VERY important to bake it very very very well. And you have to let the mix seat a couple days so it ferments a little.
We also use mud bricks for the structure.
And is mandatory to put a chimney with some sort of valve if possible.

They reach sick temperatures, if you put a piece of wood inside, it will start to burn just in contact with the inside hot air.

I'm not trying to criticize your work, I really like your oven, I just want to give some advice because I know the subject ;)

jon ball (author)DriX2011-05-28

I didn't take it poorly. Ours gets very hot. We used a wood stove thermometer and the heat was off of the scale. So, it's over 1600 farenheit. I'd be careful of the glass dust due to the risk of silica poisoning - silicosis.

As I mentioned someplace else here, we are going to remove the outer clay layer, mix in more binder material, recover it, and add a small chamber in front with a chimney.

I'll update this with the new pics as we progress.

jon ball (author)jon ball2011-05-29

I forgot to mention that we soak the door in water prior to firing.

jon ball (author)DriX2011-05-28

Yup. The Hardi Backer keeps it from burning. The chard part is because I have a slight gap there. The handles and exterior wood only get warm. The handles would get hot if I would have put the handle screws all the way through the door. But they are recessed a bit into the 2x6 - the Hardi Backer doesn't even touch them. I would think that an iron door would get too hot. Too hot to handle. (sorry, that reminded me of a song from one of my fav early 80's bands UFO)

brazell (author)jon ball2011-05-27

Thank you for posting that. I just wanted to get an idea of what you were talking about. I have tons of rocks from the creek below the house. I saw one of the commentators below say that they made one years ago from one like that and in ancient times they did as well, I may have to do some research on that technique since I have different local materials here in Alabama. Thanks so much for sharing!!! I love the taste from a wood fire oven and like the idea of not having to use that much wood.

NaturalCrafter (author)2011-05-29

What a wonderful job and willing to share the details with us here. I love just looking at it let alone it being useful! Something I always wondered and wanted to do also. Maybe someday soon...ahhhh..

splazem (author)2011-05-29

Cool! Looks amazing!

mandersen (author)2011-05-27

is it possible to design it to have a wood storage area under the oven? That would be convenient if it could be done.

neffk (author)2011-05-26

I have a 36" hemispherical WFO and it takes a lot more wood---a paper grocery bag full---to get it up to temp for pizzas. And that's real wood, not sticks and twiggs.

jon ball (author)neffk2011-05-26

We had intended to go with a 36" as well but decided that would could enjoy it and use it more if it was smaller.

neffk (author)jon ball2011-05-26

A good choice, I think. And nicely executed.

germeten (author)2011-05-26

Artfully done, but couldn't the lower foundation have been used as the
firebox, with the upper portion for cooking, baking etc.? It seems like a
lot of work and a burly foundation, just to have a relatively smaller
cooking area from which you need to add and remove coals

jon ball (author)germeten2011-05-26

We considered doing just that but decided to keep it simple. The massive foundation layer truly acts as thermal mass that radiates the heat back into the oven over time. Plus, we never have to bend over. The oven gets very hot. Though the exterior layer only gets warm to the touch.

hanelyp (author)germeten2011-05-26

The cinder blocks used on the outside of the foundation wouldn't stand up to the heat, so a layer on insulation and an inner liner would need to be between the firebox and the cinder block.

ctrimble1 (author)2011-05-26

This looks fantastic! you both did an awesome job- !!!

imthegarbageman (author)2011-05-26

I don't see a chimney.

No chimney?

traditional southwest style adobe ovens don't seem to have a chimney either. You burn wood with the door open until the retained heat is high enough and then brush out the ashes, add the food and seal the door.

jon ball (author)kill-a-watt2011-05-26

This one works great! The next incarnation will work better. Our foundation and foundation height really helps, as a heat sink and as a convenient height from which to work.

gfc62 (author)2011-05-26

Did you lay the blocks set in mortar or did you just dry lay them without any mortar or other adhesive?

jon ball (author)gfc622011-05-26

They are all dry set.

mleonard (author)2011-05-26

Quite well done! For all of us that don't know much about potting and clay can you add some info about where to get proper clay and any hints about proper use for a oven?

Thanks!

jon ball (author)mleonard2011-05-26

Well, we got ours at Goergies (http://www.georgies.com/gcc-clay-high.shtml). We used Hair of the Dog. This was our 1st WFO. It is my understanding that cob works great. This clay worked well but would have been better with a bit of chopped up straw or other "binder" material mixed in. The inside layer fired a bit hard, the middle insulation layer did its job very well, and the exterior layer of clay did not fire (bake) at all. We did not mix in flux or coat it with a water proofer because it is my understanding that part of the magic that makes great bread etc is that the whole oven breathes.

oilitright (author)2011-05-26

This reminds me of an article I saw somewhere many years ago. It was made very much like this for the foundation, only for the floor of the cooking chamber they used as I recall cement board. To form the cavity they used a paper barrel cut lengthwise about 1/3 the diameter and used the 2/3 piece like a tunnel, then chicken wire and concreted over the form. It has a chimney at the back end and a thick wood door at the front opening. It was fired with 2 large bags of charcoal. First firing burned away the paper barrel. Only this was called a BBQ and the idea was to be able to BBQ like a whole pig or a goat, lamb etc. Also made a good pizza oven and could still bake bread, even after BBQ the pig. Wish I had saved that article.

rushin2 (author)2011-05-26

Very easy to follow instructions. Thank You!!!

Steelsmith1 (author)2011-05-26

I built a wood fired stone oven in the Missouri Ozarks about 1976. I made it out of rock, which is plentiful thee, and mud; fired it with sawmill scrap, which was also plentiful at the time, and which was burned at the saw mill as waste if we didn't pick it up. I had a wooden door on it, didn't have instructions, but I had watched one used before that was brick. Yours is much handsomer than mine was! I built it so I could bake pizza as there were no local pizza parlors anywhere near where I lived at the time, It worked adequately, but would have been better if I'd known what I was doing. Nice instructable.

rhino (author)2011-05-26

Five stars, three cheers, two thumbs up, and a round of drinks for everybody!

rbbiggs (author)2011-05-26

Nice job, thanks for sharing it with us