Wood-Fired Brick Pizza Oven
This is a chronicle of my adventures in learning how to
become a bricklayer.
I've been making pizza's for a few years now, and I've
got some decent recipe's down - both pan/deep-dish Chicago style and New
York thin crust. My pan pizza's are almost, but not quite as good
as Lou Malnati's or
Zachary's, and my thin crusts are
better than most any pizza you can get here in San Francisco, but - they
need to get to the next level. My oven's good, I've got a pizza
stone, but there's still something missing. I saw
this guy in the Sur La Table catalog, and got a bug up my butt.
I'm not gonna go and spend that much money on something like that, but
it did give me the idea that I could build something similar myself.
Design Constraints
I've got a small (but very nice) backyard, so I don't
have a lot of room, and trying to convince my landlord to let me build a
permanent installation is not really in the cards. This means that
the oven needs to be portable - something that can live under my deck
and come out when I need it.
Also, I can't fully occupy the back yard for weeks on
end with all the concrete, bricks and associated detritus that goes with
building one of these things, so it needs to be a prefab job.
Something I can build in sections at my studio, bring over, and then
assemble. This will let me Dis-assemble it if we ever move.
Once I get over the hurdle of never laying a brick in my life, the
engineering of the assembly/supports will be the biggest challenge.
I'm used to having to jam 10 pounds of shit into a 5 pound sack, so no
big deal.
Costs and Materials
Most brick ovens really stress 'Thermal Mass' - the more
the better. One firing should keep it hot for a week. This
means big and heavy. Since I have to make it moveable, I can't do
that. Also, since I'll be pretty much only doing pizzas with a
live fire, and an occasional roast (Thanksgiving) I'm going to
compromise on that aspect by having just a layer of brick with a few
inches of good insulation to keep the outside temperature down.
I'm willing to use a bit extra fuel for the endeavor.
I also want to keep costs down as much as possible so
that when the thing falls apart, I don't feel so bad.
Firebrick vs. Red Clay Brick
Firebrick is the way to go - it's got (slightly) better
insulating properties - .6 or so W/mK conductivity, and will hold
up for a lot longer without showing wear, but it's expensive
($3.50/brick vs $.40). Red clay bricks are what ovens of old were
built from (think Colonial days) and are much cheaper, but will wear
quicker. From what I've read online a clay brick oven will last
for a good 5+ years before starting to show wear. I figure that in
5 years or so, I'll be in a position where I can build a permanent
installation, so I'm going with the red clay option wherever possible
start with. If I rebuild it in a few years, then such is life.
I'll have spent a lot less learning how to do this.
General Design
My base/hearth is going to be made of firebrick
tiles - 12" x 24" x 2" and I want to have an inside area
of around 2' x 2' with 3' x 2' being optimal. I'm planning on
setting it on 1" of
Mizzou Castable refractory cement. This will sit on a
supporting frame made from a bunch of spare
Unistrut
that I had from another project that will be bolted to a heavy duty
metal wagon from
Harbor Freight.
The walls will be made of red clay bricks held together
with refractory mortar. A layer of refractory cement will form a
lip on one side of each prefab section to mate each part and give some
sort of a seal. Gaps in and around the transition and chimney
section will be filled with
Kast-O-Lite 22 refractory cement.
I've been getting the refractory materials from
Pyro-Minerals Inc in
Oakland. They are really nice folks and are nearby.
The outside will be coated with a layer of Aluminum foil
to help reflect the IR back into the brick, and will also help to
diffuse any hot spots. Over that will be about 2" or so of
Kaowool
Ceramic Fiber blankets. It has a thermal conductivity of
.06W/MK. A crude FEA of the oven (assuming 600F internal
temperature, and a nominal value for 'still air' convection on the outer
surface says that the outside temp will be under 100F.
Over the insulation will be some sort of fiberglass shell that will
be decorated to make it all pretty.
05 July 2007 - I've picked up the
refractory mortar/cement/firebrick tiles from Pryo-Minerals, and gotten
a load of red clay bricks from Home Depot. I also picked up a bag
of regular mortar so I can practice building an arch and learn how to do
basic bricklaying without wasting expensive materials.
I'm modeling the oven using Solidworks - pictures of my
initial design are below. The chimney section is not done yet.
I'm sure things will change as I go along. Once the design is
completed, I'll post more details plans and an e-drawing assembly.
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Isometric Assembly of the bricks |
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07 July 2007 - First attempt at making an arch.
I've put together a form, and laid out an arch. I'm just using
regular 'Type S' mortar as it's cheap and I've never done this before.
Protip: Don't remove the form before the mortar dries, or you will
have a massive truckload of Fail. I re-did the arch (re-using the
mortar and am not expecting things to hold, but it was late in the day,
and I didn't want to go totally back to square one. It looks ok,
but we'll see.
08 July 2007 - Nope. It' didn't hold. The parts
where the mortar took are totally bonded, but where I re-used it just
failed. I figured that'd be the case, but I was just playing and
developing my technique.
15 July 2007 - Re-trying a new arch today. I'm putting
the bricks on their side as I want to decrease the weight more. I
did some quick calculations with the inside at a uniform 600F, in this
configuration (thickness = 2") and 1" of Kaowool ceramic blanket as
insulation, the outside temp is about 220F. I figure I'll need
about 2" of insulation to get it down to room temp. This will cut
the weight by over half - under 300# from over 600#.
22 July 2007 - Success!
I checked out the arch I made last week and it looks good... Well,
it's held together anyway. I was able to pick it up and move it
onto the cart, so everything seems to have held together. I also
made a 'real' arch today using refractory mortar (Tenax) - it's a lot
easier to work with, mostly since it 'butters' onto the brick a lot
easier, and seems to stay wetter longer. It's pre-mixed
(which I think helps) - I'm using it instead of trying to make my own
just because it's easier. The pail was $35, and I think I used
about 1/8 of it for the arch, so I have plenty for this project.
The layout process - First, I soaked each brick for about 30-60 sec
in a bucket of water, then 'buttered' it with mortar and set things in
place. After all the bricks were in place, I made sure that all
the joints were filled, and then tapped on them with a rubber mallet
(lightly) while holding the sides of the assembly to keep things from
falling apart.
I also played around with laying out the transition area to go from
the main oven to the entryway/chimney. It's following the standard
style I've seen in other designs, but will be a bit tricky making this
part as I need to make it a self-supporting section as part of my prefab
strategy. The bricks that are sticking out in the pictures below
will be trimmed to fit, and I'll cast concrete around them to fill in
the space.
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Test Arch - Success!
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The test arch sitting on the base
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Conceptual layout of the transition
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Back view of the transition layout
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The Mortar
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The Real Arch
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I'm still not sure what I'll do re: the chimney, but after getting on
The Google, I found what seems to be a good
reference on chimney design for fireplaces. It gives some
sketches on layout and general rules of thumb for chimney area vs
opening area. I've been trying to figure out how to hold this
whole thing together when I fully assemble it, and was trying to find
some way to use Unistrut brackets to make a frame around the thing, but
discovered that the guy I'm thinking of buying my insulation from on
E-Bay has ceramic fiber impregnated caulk for sealing kiln joints as
well. This should work well for both attaching/sealing the
sections when I put them together, but I *think* it will work for
attaching things to the base firebrick tiles as well. If nothing
else, it will be good to seal things up.
29 July 2007
Today's ProTip - Brace your Arch. The arch made
with refractory mortar separated a little bit from the outward pressure
of the structure, and developed several cracks while drying. The
parts that were actually vertical fully bonded and held, so I cleaned
off the rest of the bricks and tried again with the vertical sections
clamped to the form. Pounding the arc bricks in place with a
rubber mallet to fully compress things makes all the difference too.
This worked well enough that I made the vertical
sections of my second arch, as well as most of the back wall and a chunk
of the transition section.
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The Re-Built Arch with Bracing
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Arch, Back Wall, and Transition
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09 September 2007
The last several weeks have been a lesson in arches,
frustration, and fail. The problem I've been facing has been in
building and moving the arches. In previous posts, I've had the
bricks for the arches laid out with the 'flat' side down (eg - they are
2" thick and 4" wide.) This proved to be a major problem as the
angle between bricks was pretty big and the refractory mortar just
couldn't fill that space and have any strength.
After a few tries I trashed that layout, took the hit of
extra weight, and turned things 90 degrees. This worked out a bit
better, but there was still a lot of problems with moving the arches
from the form - as soon as I'd try and pick it up it would break in the
middle, even after letting it sit for over a week to dry. It seems
that the main problem is that the mortar doesn't get full strength until
it is fired. Finally, I got smart and opted for a 'build in place'
setup.
First up - building the frame. This was pretty
easy, just cutting some Unistrut and laying my firebrick tiles in place.
I then put the side walls of the main section on top of the tiles and
put in some extra Unistrut to hold the horizontal loading from the arch:
The next step was to build the arches in place - I did not put any
mortar on the surfaces where the arch couples to the walls so that I can
pick them up and move them after firing. The back wall and
transition section followed and everything seems to be holding together.
To keep the bricks from fully touching the frame where it needs arch
support, I put in spacers so that the conductive heat loss will be
minimal. The Aluminum foil on the bottom is to keep the tiles
clean. All the rest of the foil you see is to keep things from
sticking where I will be taking it apart. Everything seems to be
holding, and I will try a test firing pretty soon.
07 October 2007
So, two weeks ago, I got a chance to fire up the oven
for the first time - I hadn't done anything re: chimneys, but couldn't
resist the temptation. I just used charcoal for the first shot as
I didn't want to overheat things. The next week I managed to find
a place that sold terra-cotta clay pipes that happened to work pretty
well for the base of my chimney and I played around with putting that on
and casting some refractory cement around it.
This weekend was the real test. Real wood and a
'real' pizza (a frozen one from Safeway - California Kitchen 'Sicilian
Style' to be exact) I wasn't up for the full disappointment of
ruining one of my own creations, and figured if a brick oven can make a
home-made pizza great, it should make a frozen pizza decent. For
the most part I wasn't disappointed, but it took a lot longer to heat up
than I expected - I need to learn how to properly make a fire in this
thing.
ProTip: build the fire in the middle of the oven,
then after it's been going good push it back in the oven. The
brick under the fire was blazing hot, but where I put the pizza was only
around 250 degrees (the rest of the oven was 500 or so.) If I had
the fire going in the middle of the oven from the get-go, it would have
been a lot hotter. I let the fire build gradually, so it took
about 2 hours to really heat up - if I had been a bit more agressive
with the fire, it might have gotten hotter on the floor too. There
will be some playing around with technique here.
To make the chimney, I mortared the pipe in place, then
made a frame from fine chicken wire around it and the opening for the
chimney, put some plywood around the front to keep things in place and
just glopped on some refractory cement. It dried pretty quickly
and seems to be holding up well.
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The Beast without a chimney
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First Fire - Charcoal
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With Chimney Added
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Should we call the Fire Dept or Homeland Security?
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Real Wood Fire
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The Pizza
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Lunch Time!
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23 October 2007
It's now moved into my backyard - I was going to take
more pictures of the assembly, but got sidetracked. More comments
on the assembly process and 'lessons learned' to follow...
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