The Clay Oven. Part 1: Construction.

Posted by mike d. 6 comments

Sometime in early July I decided that it would be fun to build a clay oven. Like most Mike D ideas, this thought would have been better crushed under the hammer of common sense and never brought to fruition. But instead of exercising common sense, I bought a book titled Build Your Own Earth Oven and promptly read it. At the time I would rate my excitement as high. In retrospect I would rate my excitement as stupid.

The book is super hippy. It goes thourgh great lengths to describe various methods you can employ to procure all of your materials for free. Need some crushed stone? Perhaps a trip to the local quarry will help you… or you could get refuse from local construction companies! Need clay? Keep digging down, eventually you’ll find the earth you need. Then you can separate the dirt to extract the clay. Yes, it’s more labor buy you’ll be at peace with mother earth since you’ve build this oven from the earth beneath your toes. You can do the whole thing for $20.

Yeah… this seems less like a plan and more like a scavenger hunt. No thanks.

I wanted to get this done quickly so I would have been much better helped by a shopping list. So I decided to make one.

Want to build an oven? Don’t.

Still want to? Buy this stuff:

Construction materials

Base:
52 curved pavers (this should leave you with a few extra)
14 Capstones (if desired)
Three wheelbarrows full of gravel/cracked stone
48 empty beer bottles
3 bags Pearlite
~6 fifty pound bags of sand
1/2 bag clay
17 firebricks
water

Arch:
13 bricks (get the kind with the holes in ‘em)
1 bag Mortar
Plywood – Nails
water

Dome:
~10 fifty pound bags of sand
~450 pounds of clay: Hawthorn Blend recommended
1 Newspaper
16″ stick
water

Cover:
1 sheet plywood
2 ten foot 4×4′s
6 ten foot 2×4′s
33 linear feet shingles
1 small box shingle nails
3 twelve foot roof edge trim pieces
4 concrete footings

Tools:
1 Measuring tape
1 Huge bucket
1 Normal bucket
1 Tarp
1 Hammer
1 pair tin-snips
2 helpers (strongly recommended)
1 hose

This cost way more than $20. This whole sha-bang has probably run me up about $600-700 if we include the tools that I was missing. The book said an expert could do this in an afternoon. It took us something like 6 weekends – though to be fair a number of those weekends included only about 4-6 hours of labor.

Still, this is not trivial. Don’t dive in unless you’re really up for it.

Here’s my quick how-to:

Base:
1. level your working ground
2. lay out the pavers 42-44″ diameter working surface (we used a few cinder blocks to make it cheaper)

Pavers used as a base

3. fill 1/2 way with gravel
4. add some water to your sand.
4. fill with sandy mud leaving about 4″ of space for bottles
5. lay down the empty bottles – these act as insulation so you don’t lose cooking heat to the Earth.

6. mix pearlite, equal quantity sand, clay, and some water until it’s mud consistency.
7. secure the bottles in place with the mixture.
8. Place thin layer of sand on top
9. place the firebricks down: five, five, five, and two front to back. make sure they are flat and flush.

Arch:
1. Cut two pieces of plywood into a nicely shaped arch. 14″ wide at the base, 9.5″ tall in the center
2. IMPORTANT: prop the wood up on two spacers… maybe 1/2″ thick. These will let you easily remove the wood later once the mortar is dry.
3. place the wood on the front row of firebricks.
4. build your arch. secure with mortar. follow directions on the mortar bag.

Note: see those smooth-top bricks? don't use those. The arch in this picture failed.

Dome:
1. Mix some sand with water. voila! mud!
2. Shovel mud onto your firebrick. Stick a 16″ stick in the middle. Make the mound 22″ wide at the base, and have it reach to the top of the stick.

Shaun and Jen pat down the sand mound. Note the 16 inch height stick.

3. Lay wet newspaper over the finished dome.

4. Bring out the tarp.

5. dump some clay ingredients into the tarp and start mashing it up with bare feet. I hate to admit it, but this really seems like the best method. It’s hard to provide the exact formula for this, but I’d say it’s 2.5 parts sand, 1 part clay, and enough water for it to all stick together. The book recommends forming clay into a ball and dropping it. If it stays a ball – and doesn’t mush into a flat disc or break apart – you’re probably good to go.

We might be smiling in this picture, but let me tell you: This was annoying.

7. Start packing the clay around your sand dome. Pack it hard. It should be about 4 inches thick. We made ours a little thicker and it took a long time to dry.

Shaun packin' the clay.

Almost done!

8. Let that thing dry. Once the outside is stiff (if you poke it with your finger it doesn’t do much more than indent slightly) walk around and bat it down with a board to smooth out the surface. Stop if the clay sticks to the board. Our oven was partially in the shade, this required TONS more drying time. We’re talking a solid week of drying. Also, it was super rainy which didn’t help. So we had to keep covering it with a tarp.
9. Once dry, dig out the sand. Don’t dig past the newspaper. (note: in this picture the arch is gone. That’s because it fell apart cause I used smooth-topped bricks)

Kevin digging out the sand.

10. start a small slow fire and burn that bad boy in SLOWLY.

Next up? The shelter!

The weather can damage an oven. Build a shelter for it. We did it with a simple lean to. Nothing special here, I’ll just post a few pictures.

Shingles in process. This was a quick and easy cover, so we didn't bother with tar paper. I'm not expecting my shed roof to last 30 years but I'm okay with that.

Inside the oven.

Complete.

In that last picture, we’re doing the burn in. Note the new arch that was done with the proper bricks as well as the sweet trim along the top edge of the shelter. I think I’m going to buy some lattice to put up on the back and sides to protect the oven from wind-blown rain and snow drifts.

Also, I still have to put some insulation on the oven. Apparently a mud, straw, clay mix will do it. I’m pretty stoked about this whole thing, but holy moly what a pain in the butt to get together. If you’re really insistent about building one of these things let me know and I’ll do what I can to help.

In Part 2, I will talk about the first cooking experiences. Here’s a preview:

FIRE!

6 Comments
Sep 20, 2011
7:59 pm
#1 Mika :

I am beyond impressed with your dedication! I can’t wait to hear how the first successful meal went!

[Reply]

Sep 20, 2011
9:27 pm
#2 Tom :

A pizza oven figures into my long term plans for building the ultimate outdoor kitchen/grill/bbq. I haven’t done too much research into the pizza oven aspect of it yet though, so I’m excited to hear about your experiences.

Any worries about frost heaves?

Can you elaborate on why the first arch failed? Why don’t the smooth bricks work?

Are there fire codes to be aware of?

[Reply]

mike d. Reply:

Tom!

Frost? yes. I am worried. We have a crack that formed. The book said not to worry too much if you get some cracks, but it is expanding. I do worry about how the cold winter will affect the structure.

Turns out there’s a reason masonary bricks aren’t smooth. The mortar has a hard time sticking too it. Those decorative flat bricks don’t have the purchase that the ones with holes do. In structural applications they can’t keep up.

I’m not sure about the fire codes for your state. Actually, I’m pretty sure Massachusetts allows any burning provided it is for the purpose of cooking food. Probably worthwhile to look into this one.

[Reply]

Tom Reply:

You’re right about the cooking, just found this in the Mass fire codes:

“Persons 18 years of age or older may, without a permit, set, maintain or increase a reasonable fire for the purpose of cooking, upon sandy or gravelly land free from living or dead vegetation or upon sandy or rocky beaches bordering tidewater, if the fire is enclosed within rocks, metal or noncombustible material.”

But I was also thinking things like how far the oven would need to be from other structures, and any requirements or restrictions for a covering structure. But I haven’t found anything specific about that. I’ll probably have to call the local fire department at some point.

[Reply]

Sep 21, 2011
3:15 pm
#3 Tullio M. :

Hi Mike,

First of all I would like to congratulate you on your successful build, it looks amazing, almost as if professionals did it ;) second, what would you say your total cost was for this build? I have been wanting to build one of these for a long time and I would like to get a budget worked out. Thank you,

Cheers

[Reply]

mike d. Reply:

I saved receipts, so I might be able to tally the exact end dollar value. But I would guess that the end amount was around $650 dollars.

[Reply]

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