Several years ago, I wrote about how to build (the now-infamous) $20 outdoor cob oven. That oven I built worked decently, produced a lot of delicious meals, and advanced my pizza baking fever to new heights. Since then, we’ve built several more outdoor pizza ovens, and each of them has been a great improvement upon the original.
This newer model is slightly bigger, allowing for easier access to the oven interior, it has even more food baking potential, and the insulation is vastly superior. This sucker gets hot, and stays hot… for a long, long time. The oven has a small roof shelter, protecting it against the weather, and a chimney keeps smoke out of the face of the fire tender. Best of all… the oven is still very inexpensive to build.
This is a very achievable, low cost, and effective oven that will not cost you thousands of dollars to build. Here’s a look at the new and improved outdoor pizza oven plans and how you can build your own.
The Better Outdoor Pizza Oven Plans: Overview
The oven I will propose and outline below is a highly insulated cob oven. For the uninitiated, cob is a combination of clay, sand, straw, and water. When dry, cob is extremely hard and durable, and highly capable of storing heat (given enough insulation.) The focus here is, of course, building with natural and recycled materials whenever possible. This oven is designed to be very inexpensive, consisting of materials that should be widely available.
The oven is no slouch in the baking department, either. With a 27″ diameter interior, you can comfortably cook two small pizzas at the same time while maintaining a small fire for cooking the toppings. We’ve made up to 60 or more pizzas in a cob oven described below, and they still cooked in 3-4 minutes after several hours of use. Needless to say, this sucker is very insulated. Not to mention, the range of other baking possibilities is vast — bread, roasts, pies, cookies, etc. are all fair game, assuming you have the gumption to prepare all those foods and harness the tremendous heat from the oven. This is much more than a just an outdoor pizza oven — this is a highly versatile, powerful baking tool.
Ok, let’s get on with the building plans…
Don’t Just Throw it Anywhere: Siting Your Oven
Siting your oven is an important consideration, and can make the difference between an oven that you rarely touch because it’s too far and isolated from your home or main kitchen, and an oven that creates its own positive space with ample room to prepare food for baking and to gather eager friends around for a big pizza party.
Questions to consider include: how close will it be to your existing indoor or outdoor cooking space? Will there be enough room to build around it later, if need arises for space to seat your growing posse of pizza-loving guests? How close is your firewood storage? What kind of shelter will you construct? Once your oven is built, it ain’t moving. These suckers are permanent fixtures.
Build a Sheltering Roof
If you live in anything but a dry desert climate, I am going to insist that you build a sheltering roof to protect your cob oven. Rain and moisture can quickly take a toll on an oven made of mud, and firing anything but a perfectly dry oven will be an exercise in futility — why spend more fuel and time drying your oven when it already takes a couple of hours to get the cob up to baking temperatures? An oven that continually gets wet will require a whole lot of on-going maintenance work, as well. It makes excellent sense to go ahead and build the shelter before you start the oven, too — this way you can safely protect your work while construction is happening. (It’s also difficult to do framing work around the obstacle that is the oven itself.)
The absolute minimum shelter I consider acceptable for the oven I will describe below is about 7’x8′. (These dimensions are for the frame — the roof overhang will add another 2′ to each dimension.) This is what we recently built for friends, based strictly on the limited materials they had on hand. In an ideal world, I would factor in at least two feet of roof protection on each side of the oven, and additional space for a prep table to roll your pizza and bread dough, stage other food to be cooked, etc.
Local weather conditions will dictate how you design your roof, but the simplest solution is a lean-to shed roof with enough overhang to protect the oven and the frame itself. The options for a sheltering roof are literally limitless, and it can be as simple and austere, or extravagant and beautiful as you want it to be. Whatever you decide, just make sure the roof extends as least enough to protect the oven from blowing rain. Again, space for food prep is highly recommended as well. You’ll be much happier this way.
Dig a Drainage Trench
Cob ovens are extremely heavy. A foundation helps support the weight, raise the oven off of the ground to a comfortable working height, and should include sufficient drainage to protect the oven from freeze/thaw and other moisture damage.
To that effect, you need to go down before you go up. Start off by measuring a circle as large as your desired oven. My recommendation is a 27″ diameter oven. (Note: that means the interior cooking space is 27″.) For a 27″ oven, you’ll need a foundation much larger than that, however. Factor in another 8″ for the cob dome itself (4″ thickness around the entire sand form), 16″ for insulation, 3″ for plaster, and another 4″ for the diameter you may lose as your foundation grows taller and tapers inward. That’s about a 58″ diameter foundation.
You’ll want to mark out your desired size on the ground, and dig down, removing all the topsoil in place. Ideally, you would dig down as far as your local frost line, but you may choose to go less depending on what is convenient. If you don’t expect to have your oven around for the next 100+ years, it may be less important to dig that far down, and perhaps get at least 18-24″ deep to deal with 95% of all threats of freeze/thaw damage. (If you live in a southern climate, it may not even be a concern. Lucky you, in that case.)
Either way, dig a hole as deep as you deem appropriate, and dig a connecting trench downslope that will carry water away from the foundation. The trench should exit the ground at daylight, meaning the trench needs to be as long as necessary to be able to exit at the surface of the soil. Put a 4″ perforated pipe in there for the best drainage, or simply backfill it with gravel. The deeper you dig your hole, the further you’ll have to dig your daylight drain. The greater the slope on your land, the less distance you’ll have to cover. Make sense?
Backfill your new hole with gravel. Gravel is an excellent drainage medium. Any water that finds its way under the oven will fall easily through the gravel, and then be carried away from the site once it hits the bottom of the hole, and finds the daylight drain. Be sure to tamp every 6″ of gravel — don’t just dump it all in there at once! Tamping ensures that the oven will not settle in any unpredictable ways. You could also stick a perforated pipe under the oven to ensure optimal drainage.
Building a Solid Foundation
The foundation, as stated above, serves several functions. It’s also an opportunity to define the character of your oven. Stone is an excellent, timeless choice, either dry stacked or mortared. In areas without stone, brick or busted concrete (a.k.a., “urbanite”) make good alternatives. If you have a bunch of homeless cinder blocks around, that could work equally well, though they aren’t as attractive as the other options. Other options could include a wood crib, designed like a log cabin with notches on the corners and backfilled with rubble or gravel (but make sure the wood is insulated from the heat of the oven, in this case), recycled tires filled with busted up junk…. be creative.
We opt for stone wherever possible, and build up at least 18″, but preferably 36″. In cases where we don’t have enough stone to go the full height (more on that in a minute), the remaining height can be built up with cob. The stone is dry-stacked around the perimeter of the drainage hole, and filled in the center with all manner of crappy broken bricks and busted concrete. That stuff will never be seen again, so the center of the foundation is a good way to use your worst material.
A 40″ height is a recommended average hearth height, so your foundation should be nearly three feet tall. (The hearth insulation and firebricks will make up the last few inches.) That ends up being quite a fair bit of material! Don’t underestimate how much stone or rubble you’ll need.
Insulating the Cooking Hearth
Insulating the cooking hearth is crucial to taking full advantage of the blazing heat of your oven. You can use several materials, or a mix. We use either a combination of beer bottles and dry perlite, or straight perlite.
The advantage of using beer bottles is their wide availability, of course. Using straight perlite without bottles eliminates the need to “cap” the insulation layer with cob (which will leech at least some heat from the firebrick hearth). Perlite also offers excellent insulation values but is dusty and synthetic, and obviously more expensive than throwaway bottles. The choice is yours, however. I have not noticed a significant performance difference between using a bottle and perlite mix compared to straight perlite.
A good 4″ layer of insulation is an okay minimum, though you may want to aim for a full 6″. (In my firing experience, 4″ seems adequate for the job. By “adequate” I mean that one oven we built with this method still demonstrated excellent heat retention in the hearth.) Build up a thin cob wall all around the perimeter of the oven foundation to contain the insulation material up to the height of your desired insulation level.
Note: If you did not use any cob to bring up your foundation height earlier, you’ll want to create a nice level surface with at least an inch or two or material prior to this containment ring step, as well.
Spread your beer bottles within the cob containment ring, and be sure that none are touching. The less they touch, the less chance something will shatter down the line. Once they are arranged, go ahead and dump your perlite, and please do make sure you are upwind of the dust!
The next step can be eliminated if you use straight perlite: go ahead and use some cob to “cap” the insulation. Try to use as little as possible — an inch will do it. You should simultaneously create a nice level plane for the firebrick hearth. A trowel should help in establishing a smooth surface. Try your best to eliminate low spots — this cap doesn’t have to be 100% perfect, but the closer to level the better, of course.
At this point, I would wait until the cob cap fully dries before preceding. It shouldn’t take long with a day or two of sun and wind. If you don’t wait, you risk the chance of your firebrick hearth settling.
Build a Fire Brick Hearth
Fire brick is a block of refractory ceramic that is much more capable of withstanding high temperatures than typical red building brick. They range in cost from $1-$3 each brand new, but it’s likely you can find some used with a bit of searching. Check craigslist, or get in touch with local potters who may have some extra lying around from a kiln build. I’ve been able to get recycled bricks for $1, and new bricks for as little as $1.35 each. Be sure to get bricks that are at least 2 1/4″ thick, if not 2 1/2″. (That 1/4″ doesn’t seem to make a huge difference, but work with what you can get!)
Fire bricks make a lovely hearth capable of withstanding a very hot fire, and they store heat that will help bake your pizzas through the power of conduction. Laying them out is very simple, as they do not need any mortar.
Determine the center of your oven, and mark it with a scratch or twig. You’ll want your entire hearth pushed forward of center, as the “tongue bricks” should overhang the front edge by an inch or so. Using some sifted sand free of pebbles, lay out a thin, level bed for your firebricks. (You can run sand through a 1/16″ window screen to remove pebbles and larger particles.) You will need 18 bricks for your cooking surface, and another four for the tongue/door support. Line up and center the tongue bricks, and try to hang them off the edge by a good inch or so. (This will make it easier to hold an ash can under the hearth when sweeping coals out later.)
You can lay out the remaining 18 bricks as I did in the image above, or do 3 rows of 6 bricks each. P.S.: the reason 27″ makes a great oven size is that you are using the maximum surface area of the fire brick. Fire brick dimensions are 4.5″x9″, so 6 bricks x 4.5″ wide = 27″ wide.
When placing fire brick, be sure that you slide them downward into position. Do not get sand between the bricks. Use the butt end of a hammer to set them and to make tiny level adjustments. Your bricks should be level and flat — the flatter the hearth (meaning, no brick corners jutting up), the better your cooking experience will be. You don’t want your crusts or bread getting caught up on anything.
Don’t be afraid to start from scratch if need be — setting the hearth doesn’t take much time, and once it’s set, it’s set. There’s no changing things later.
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