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In this video, we’re going to show you how
to build an earthen oven.
The existence of ovens like this is easily
documented for the 18th century. In fact,
just about every ancient culture had a very
similar oven. There’s one particular wood
cut illustration from medieval times depicting
an earthen oven built on a wagon. There are
references in 18th century literature and
also archaeological evidence that you would
find ovens like this in private homes and
in fort settings. There are also references
to communal ovens where the baker would bake
bread for an entire village. We’re going to
need several things to make our mud oven out
of. We’re going to need sand. That’s the major
component of our oven. We’re going to need
a good bit of clay. This is dried clay you
can get at a masonry store or you can get
damp clay out of ditch bank. You’re going
to need straw or dried grass or maybe hay.
You may need some bricks, so some fire bricks,
even regular bricks will work, and you’re
going to need a canvas tarp to mix your cob
together with and you’re definitely going
to need a good bit of water.
Before you build your oven, you have to consider
what you’re going to build your oven on. There
are historical examples of ovens built on
tables or on brick or stone plinths, on hearths.
On the top of our very sturdy table, we’ve
laid out a layer of fire brick. That’s going
to be the floor of our oven. We’ve also chalked
out here the design. About 22 inches across
to the bottom on the inside. That’s the inside
measurement. The walls are going to be about
6 inches thick so we’ve got markings here
so we can see about how big it’s going to
look on the surface. The door width right
here is about 12 inches across so we can
get something as big as a pie in without too
much trouble.
First thing we’re going to do is we’re going
to build the core. It’s going to be like a
sand castle, just wet sand that we’re going
to build the oven over the top of. Sometimes
you’ll see other people doing it with sticks
and things like this, but this is going to
be much easier and quicker. This is where
our door is going to be. I just went ahead
and put a couple of bricks in here to be the
inner core of the door. They’ll be removed.
And right here I placed a brick wall to give
us a nice flat surface to build up against.
So we’ve taken about an hour to put this together.
We’ve used very wet sand so that it stays
into shape. Now we’ve got to make sure that
this stays wet until we get our first layer
on. There aren’t very many critical things
about the shape and the size of your particular
oven but there is one critical thing, and
that is the height of the opening tunnel here
compared to the height of your dome. These
need to be a particular ratio or else the
air won’t draw through this when you’re burning
the wood inside of the thing. So, this is
between 65 and 60% or about 63% height here
compared to the height there.
The next thing we’re going to do is put paper
on this. We’re going to put paper, we’re going
to wet it down so that it’ll give us a layer
to separate so when we take the sand out it
doesn’t stick to the inner surface.
We’ve got the paper covering done on our sand
inner core. This will make it much easier
to take the core out from underneath it. Now
it’s time to make the first layer of cob or
mud to put on our oven.
This inner most layer of mud or cob that we’re
going to put on our oven is just sand and
clay. About 2 parts sand to 1 part clay. You
mix those two together so that they’re very
well mixed and then we just put it on there.
We want to make sure it’s got about the right
consistency that we can still work it but
it isn’t so wet that it’s sloppy, and you
want to make sure to have err on the side
of a little more sand than too much clay.
The more clay you’ve got the more it’s going
to shrink and crack.
So you probably want to make up a bunch of
this cob beforehand. It ages well. It won’t
go bad waiting overnight, and that way, as
soon as you’re done with your sand castle
core, you can start putting it on right away
and you don’t have to worry about that drying
out and blowing away while you’re making your
cob.
So, learning just the right consistency can
be a trick. As you see here, I’ve been stomping
on this pile for a little while and this is
starting to feel really good. It forms up
into a ball, like a snowball. It doesn’t deform
easily. It’s not sloppy and you can still
form it into any shape you want and it’s not
too drippy either. That’s what you’re looking
for, something that holds together well but
still moldable.
So we’re working on putting this first layer
on. This is a layer without any straw in it
because that would just burn up anyway. It’s
about 3 inches thick and we’re starting at
the very bottom and we’re going to work our
way up, that way we can watch as we go to
make sure our thickness stays about the same.
Well, we finished the inner mud layer yesterday
afternoon and we let this set overnight and
it’s just slightly firmer than it was. We
don’t want to let it get too dry or else the
next layer won’t adhere to this layer properly.
We’ve scratched this layer a little bit so
that the next layer of cob we put on here
will adhere nicely. This next layer of cob
that we put on, it’s going to have grass or
hay or straw in it to give it a lot more strength
than this inner layer.
We’re going to mix our clay and our sand first.
As soon as that’s getting close to the right
consistency, that’s when we’ll add our other
binding material here.
So, we’ve got this mixed up. I’m going to
mix this up just slightly wetter. It’s feeling
like a pretty good consistency now under my
feet and since we’re going to add in this
dry straw here, it’s going to dry it up a
bit so I’m going to start with slightly wetter
mixture, but we wanted to get this mixed first
and then add in the binder.
This will add some amazing strength to it.
When it dries up it really binds it together.
So it’s helpful to make this cob up beforehand.
It really makes it work better if its couple
days old, but you don’t want to let it get
too old because as it’s wet for a long time,
the grass will start to rot in there, so you
don’t want that to happen. If it’s a day or
two old, keep it wrapped in plastic so it’s
wet and pliable. It’ll really work even better
after a day or two.
So, to make this go faster, I suggest you
invite a bunch of friends over. Have a cob
party. They can be stomping on this stuff
while you’re putting it on your stove. Everyone
will have fun.
Well, I’ve got about five or six big loaves
of cob here ready to go. I think that’s a
good start. I’m not sure exactly how many
it’s going to take to cover this oven, so
we’re going to put this on and then I’ll see
how much more I need to make.
I’ve got marks here on the table to get about
2.5 to 3 inches for the outside layer. I’m
going to start putting on our loaves. We’re
going to make sure they butt up well with
the inner core here so there isn’t a big air
space between them, and I’ll just start adding
these on all the way around.
Okay, there it is. We’ve got the second layer
of a cob type material on here. This is the
stuff with the straw that’s built into it.
It does, as you work it, it kind of sags down
some so you might want to start a little thinner
at the bottom than the finish, expecting some
of it to sag down into position a little bit.
This gives us a good opportunity to look at
the cross section of what’s going on here.
You can see the cobs a little thicker down
at the bottom than it is at the top because
it’s kind of sagged a little bit. You can
see our outer cob core, our inner core that
doesn’t have the straw in it and here’s the
sand core on the inside. We’re going to add
a little bit to the outside here. We’re going
to give it a nice rounded opening because
a rounded opening is going to have more strength
than this sharp edge.
Well, we’ve finished putting our rounded opening
on the oven so it will be a little bit stronger.
We made sure to make the cob that we added
back into this outer stuff. Whenever you add
two pieces together you really have to work
it so that the two pieces adhere to each other
and it just doesn’t fall off. We added a little
bit of sand on the front to help support that
lip. Depending on where you’re at, your environment,
the time of year, what the humidity is, this
will take 2 weeks, 3 weeks, 4 weeks, maybe
even a little bit longer for it to get dry
enough for you start to even think about warming
it up from the inside.
While this is drying, you don’t want it to
get rained on so you’re going to protect this
from the weather but don’t cover it with plastic
so that it can’t dry. So you want to protect
it from the rain but let it breath
So, it’s only been about 24 hours since we’ve
been here last, but it’s firmed up enough
with how the weather is here that we were
able to go ahead and pull out some of the
sand. I haven’t gone and dug the whole thing
out but I want to let it start to dry out
on the inside and even peel off some of the
paper if you want to. That will all burn out
anyway, but we just dug it out about halfway.
We’ll come back in a couple of days and take out more.
We’ve removed the sand core from this oven
and we’ve given it a couple weeks to dry so
it’s almost ready to fire. You may not have
to wait this long if you build an oven but
if it’s not adequately dry before you fire
it, it will cause cracking or at least more
cracking than normal in the body. Even if
you wait like we did, it’s inevitable that
some cracking will occur. Don’t be alarmed.
If the cracks are especially big, you can
repair them with a little extra sand and clay
and let that dry in place.
We’ve employed a few warming fires in this
oven and it’s dried out well. We’ve gotten
a few cracks but overall we’re really pleased.
The walls of this oven are extremely durable.
Here’s a brick of the material and it takes
a lot to break this material up, so if you
need to do modifications, you’ll really have
to chop at it. However, as sturdy as this
is, it still needs to be protected from the
weather. This is water soluble and it will
just wash away with the rain, so if we need
this to last a while we’re going to have to
build a little roof over it.
Make sure to watch part 2 of this video where
we learn how to bake bread in one of these
earthen ovens. You know, this looks pretty
good. I think I’m going to fire it up.