Wood-Fired Brick Oven





Introduction: Wood-Fired Brick Oven

About: hmmm...

This article is about the brick oven I made in my back yard. There are lots of similar articles on the interwebs, but I decided to post mine anyway.  There are a lot of variations, so my oven may be informative to others who are designing their own oven.

Just to be clear, this is a black oven.  The fire is burned on the hearth.  Before cooking, you have to move the coals to the back of the oven (for pizza) or sweep them completely out.

Mr. Wikipedia says:




Step 1: Foundation

There are basically 2 methods for making a foundation: slab or footings.  I used a slab because I felt that the weight and geometry of the oven did not require footings.  A house, which weighs much more and is distributed over a much larger area, requires footings.  Variation in soil type and moisture level in the soil at different locations around a foundation are more likely to occur for buildings that have a large footprint.  This little oven is light and compact in comparison and does not need such an elaborate or expensive foundation.

Step 2: Base

The oven proper must be the correct height for you to enjoy using it.  A rule of thumb is that you should be able to see the back of the oven without bending at all.  I am 6'3", so my hearth is very high indeed. 

To lift the oven to this height, I built a masonry platform.  Many people use cement blocks---the type that basements are made from---to create the platform.  This is all well and good, but I thought it would be more fun to build a brick platform, with a circular arch.

One source of difficulty was that I didn't really calculate or even try to estimate how many bricks I needed.  I bought a pallet of 500 bricks for 0.20 ea and figured that it was really cheap and a lot---probably enough.  It was not enough---half, at best.  I had to use stones from a farmer's pile for fill and facing on the sides.  This added considerably to the difficulty of the project, both in time and effort.  The round edges of the stones make them difficult to work with.  I adopted a slip-form technique, in which rocks are piled against a form (the boards) and concrete is poured in from behind.  The result looks terrible.  My wife suggested stucco over the whole mess and I can't disagree.

I did try to calculate the load-bearing capacity of the arch.  For my oven, the bricks and mortar are a lot stronger than needed.  But for your own oven, you should run the numbers or find someone who will.

The arch was made, step-by-step using a form made from a section of 2x4, 1/4" plywood, cardboard, and shims.  First, I put the form in place, raised on extra bricks and shims (so you can get the forms out!).  Then, I crinkled up the cardboard and put that over the forms.  Then, I mixed up some mortar and put down a few rows of brick.  The next day, I pulled the shims, moved the forms, and did another few rows.  The brick had holes in them, so I eventually covered the holes with flat rocks and cement.  It would be better to have turned the bricks on their sides, but I didn't think of that until long after the mortar was hard.

I filled in the "legs" of the arch with rubble.  My neighbor gave me a bunch of rocks and I added in glass bottles and several years of saved brick, cement, and other stones that I had saved for the purpose. 

Eventually, a stable flat platform was finished.  I kept it covered to keep water from going down the holes in the brick.  Water seems to be one of the main causes of masonry problems, especially when you live as near to the north pole as I.

Step 3: Oven

There are two types of oven shapes: spherical or cylindrical.  As you can imagine, orthodoxy and opinion dominate the pointless discussions of the proponents of each shape.  Mine happens to be spherical.

I made the hearth from firebrick.  Each brick is 4.5 x 9 x 2" or so.  Some would have you lay them bricks so that the oven floor and dome is 4.5" thick, but that seems to take 250-300 bricks.  Each brick cost me 2.10 USD, and my budget was too small to accommodate such a design.  Instead, I brought 60 bricks and 100 lb of dry refractory cement (HeatStop 50).  It was enough, almost.  I used a few old dense bricks to finish off the top of the dome.  I intended to use firebrick for the hearth and the first row of bricks, but had enough for almost the whole project.

I put down a layer of polystyrene insulation and put a thick layer of concrete mixed with vermiculite.  This all served as insulation for the hearth.  Unfortunately, I made this base circular.  It would have been better to make this entire part of the oven square, so that the firebricks on the edges would not have to be trimmed.  In some cases, I had very small pieces, which were an irritation throughout.  The 8" layer required almost 4 cubic feet of coarse vermiculite.  It was structurally sound within a day but remained soft and spongy for about a week.

Above the insulation, I put a thin layer (1 in) of portland cement, which served to level the hearth.  Then, a layer of sand, followed by the firebricks.  If you follow this design, skip the sand.  It makes the bricks on the edge of the circle unsteady.

After the hearth was finished, I began adding the first course of firebricks that make up the dome.  The first course was easy because each brick can be made to fit will (minimize mortar joint) with a single angled cut.  Farther up the dome, it is much harder.  Dry fit the bricks before you mix up the refractory cement. 

I made the forms for the oven dome out of foam insulation.  It was harder than I expected.  Once the forms were in place, I continued adding bricks until I got to the top. 

Step 4: Roof

Ovens are made weather-proof in a variety of ways.  I made a gabled roof over mine.  I wanted to cover that ugly igloo shape, which I think looks odd and out-of-place.  I wanted an over-hang to protect me from the elements while I wield the peel.  I'm planning on using this oven year round, and it rains and snows here.

I cemented several pieces of 2x4 lumber to the base of the oven.  These vertical members were reinforced with cross pieces that formed strong triangular sections.  On this frame, I added rafters.  On the rafters, I placed OSB, roofing felt, and asphalt shingles.  The rafters were triangular with 6" of overhand on the sides.  Above the dome, there was not enough clearance to allow for adequate insulation, so I made a metal crosspiece and used a reciprocating saw to remove the original wood member.  On the front, I made the crosspiece shorter and higher to accommodate the cook's head.  If I were to do this again, I would make the pitch of the roof a little higher.

I should have built the chimney first, but I was getting tired of dealing with the plastic cover every night.  Instead, I left a hole.  In anticipation of the flashing that would go around the chimney, I left some of the shingles loose around the edges of the hole.

The flashing around the roof was the hardest part of the project.  It would have been a lot easier if I had known what to do and done it in the right order.  I think I spent more time sealing the roof around the chimney than on any other part of the oven. 

In frustration, I used a lot of roofing cement, built a chimney cap, and hoped for the best.

The chimney cap was fun to make.  I measured the irregular top of the chimney (kids, when you build the chimney, don't make it like this one) and made forms out of the polystyrene insulation. You can see that there is a drip groove that goes around the edges.  The base of the cap was custom fit to accommodate the ridiculous jagged top of the chimney.

Step 5: Door

When I first started using my oven, I used bricks for a door.  The door is used to help avoid heat loss while baking (after the fire is raked out).  Bricks are fine, but the didn't seal very well and they were always in the way.  So, I decided to make a better door.

I cast a cement door in-place.  That is, I made a form that included the doorway of the oven, the inner arch that is made of firebrick.  I used wax paper to prevent any sticking and was careful to avoid permanently cementing the oven closed.  I packed my forms full of 3000-psi concrete (2:3 portland to sand, instead of 1:3, which I used for everything else) and patiently waited for it to cure.  Full strength, I've read, does not come for almost a month.  In the concrete, I included wire mesh for strength and 1/4-20 bolts for attaching the hinge. 

I had to make a double hinge because the oven opening is so far back from the front of the oven and because the opening is already too small for a simply hinged door.  Instead, it's a 4-bar linkage---door, 2 links, and ground.  It's important for the two links to be rigid.  I've used 1-1/4 x 1/8" angle from a bed frame (probably mild steel) and 16 ga sheet metal.  The length of the two links depends on your oven.  The mounting plates on either end of the hinge are 4 x 12 x 1/4" mild steel.  I wanted some ability to make minor adjustments, so these plates are mounted with 1/4-20 machine screws instead of being welded.  The rest of the connections are welded. 

The joints are made with steel round stock, about 0.300" in diameter.  I flatted the ends of the shafts slightly with a file and drilled a hole for a cotter pin.  The filing makes drilling holes easier because the drill bit doesn't walk around.  I think a punch would also do the trick.  I didn't have any cotter pins, so I used a small nail, instead.

The whole hinge needs grinding, priming, and careful painting with a good exterior-grade "enamel" paint.

Just the construction took me about 10 hours.  Granted, I cut everything with a hack saw and I'm rather green when it comes to welding.  Still, it's an undertaking.  Many people use simpler doors that may better match your work ethic and are perfectly functional.  I like this design because my dome construction was sloppy and casting a door was a lot easier than whittling.  I have also been reading about linkage design, so this was a chance to put some theory into practice.  My inexperience welding was also a factor because I've been looking for metal-working projects so that I'll have a reason to practice. 

In conclusion, I can't tell you what kind of door is best---only that this is the one that I made.

Step 6: Use

Time to fire up the oven.

Many people have feel that it is terribly important to gradually heat up a new oven.  I'm not sure if it's required, but after putting in so much effort, I opted for the more conservative route.  So I built several small fires in my oven and then a big one.  I'm also told that if an oven is left un-used for a long time (months) it's a good idea to heat it up slowly.  Anyway, I like to do a pre-heat fire the day before I need the oven, so it's all the same to me.

I knew it was really hot when the soot burned off the top of the dome!

Now, it's time to figure out how to bake a pizza.  You'll need a peel, shovel, metal bucket, wood, friends, dough, and toppings.  But that's a whole other instructable.



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    A local here built an oven from adobe. he used willow withes to make a rough basket then cover it in damp newspaper to form the mud over. after the oven was built he fired it with a slow fire and burned all the paper and willow away. That's how I'm building mine.

    the polystyrene scares me. It's toxic if it burns or melts... is it necessary? Heat rises and all, but It still throws up a flag in my mind.

    2 replies

    Good question. I had to make a number of design choices based on the empirical (and probably unreliable) experience of others. There was a great deal of emphasis on the under-hearth insulation, but I'm not sure it matters much. The same camp claimed that 8" of insulation above the dome is needed, but I have 2-3" and it never gets ofer 160 oF near the outer edge of the unsulation. Point is, you could probably do without it. The vermiculite concrete is probably adequate.

    Foam insulation is basically a solid form of petroleum, so you're right to be worried about it. However, I don't think there's much danger in my design.

    So that temp measurement was wrong. I now have 4-6" vermiculite insulation over the dome, which is enough. More would be better.

    Some notes on footings for people who may be planning their own projects:

    * If you are building in an area with cold winters, you may want to dig the foundation down to the 'frost depth' for your area. You can get this information from your local building or planning department. This will prevent the footing from being moved up and down by the soil freezing and thawing which could break up your masonry structure, or cause it to lean. A deep bed of compacted gravel would make an acceptable substitute for full concrete foundation, as most of the water will drain out of it.

    *I would locate something like this away from large trees, especially if using a very shallow foundation. The tree roots will eventually move the foundation.

    2 replies

    are you a code enforcer or an insurance agent? LOL :)

    I believe the author is in Minnesota, if it's like Maine, no one is really going to dig down 6 feet to get below the frost line. That would be a huge hole.

    The purpose of footings is to support heavy objects and to prevent un-even shifting of a foundation. My oven is quite light compared to a house and it is on a slab that isn't even 6' square. If the ground heaves, the entire structure should move together, not crack.

    Excellent Instructable!

    If you ever make another one:

    One traditional (oldey tymey) way of forming the dome (beehive) is with moist sand. Make a dome of sand and lay your bricks over it. Once the mortar has set, scoop the sand out.

    3 replies

    Good point. It is a lot of sand, though.

    I think my form was really poor and unpleasant to work with. There are still bits of pink foam in my yard from the struggle to get the form out!

    Making forms, I think, is boring but very important. If I were to make another oven, I would make the forms FIRST.

    I used the sand method and after dumping the first bag of sand in I was like... HOLY COW thats going to take alot of sand. I called some friends and had a whole bunch of empty quart pop bottles(lids on) and olive oil cans (same) deliver to take up space. I also used a beach ball.It was the best because I put the valve toward the opening so deflation created an opening .

    The beachball is pure genius!

    great job : that's how all ovens should be wood cooking gives such a nicer tast e!!…

    3 replies

    It is fun. But having used it for a while, I have to say I appreciate my electric oven, too. It's fun to have a baking day, starting the fire 4+ hours before baking, but it's really too much for a single family. I'll have to get my neighbors involved. And it's cold up here in MN, so it becomes a chore to bake in the winter. Still, I'm glad I built it.

    Good idea to have your neighbors involved. It will make your oven a friend maker !…

    Otherwise let it be a summer oven.

    I was wondering : the small roof over the oven seems a little bit too close to the top of the oven (despite insulation). What do you think ?…

    It would be nice to have a little more clearance. I measured the temp just under the surface of the vermiculite and it gets up to 140-160 oF. I think it's safe enough, but if I was building it again, I'd leave another 12" or so.

    how long does this take to heat for pizza or bread. It seems to be more inductive heat rather than direct (i.e. heat the oven from below without burning wood inside vs. burning wood in the oven) Or is the bottom just for wood storage? Would love to see the oven 'in action'. Good tutorial too.

    3 replies

    It takes about 2.5 hours to get it up to temperature.

    It's a black oven, which means the fire burns on the hearth where you eventually cook food. Obviously, some effort is needed to minimize the amount of ash that ends in the food. I use a wire-bristle brush to which I've attached a long handle.

    After pizzas are made, there still a lot of heat to be used. After people left the first pizza party, I cooked a pumpkin and roasted a chicken. The oven was still 300 oF the next morning. I fired it that night for more pizza, and am cooking chickpeas, 2 more large pumpkins, and my wife's chili-lasagna invention. I'll dry some pumpkin seeds, too. There'll still be lots of heat left over. I'll have to coordinate with my neighbors next time...

    Cooking pumpkins?

    Right. We had a lot this year and I don't have a proper root cellar for storing them. I seeded and sliced the pumpkin and piled the slices in a casserole. I cooked them for a long time---over an hour. Then I scooped the flesh out and froze it in quart bags. The next week, I cooked 7 more pumpkins. There was still room in the oven for more!