A 32" Cast Pizza Oven in CT, USA

[WaterDog]

Things have been a little quiet around here on the build front so I thought it might be a good time to share mine.

I began baking bread over 15 years ago, and making pizza became a natural outgrowth of that. Over time, I’ve tried many different ways to make a great pie including: the Jeff Verasano oven hack, the FrankenWeber propane fired 'blow torch', various oven techniques (stones, steels) and a dry-stacked firebrick WFO.

All had moments of triumph but ultimately I knew a ‘real’ WFO was inevitable. Living in the New York City metro area my entire life, I've had many great pizzas from New Haven to NYC to Jersey. As more authentic Napolitano places emerged in NYC like Keste and UPN (back before Anthony went west), my horizons expanded. I became pretty good at replicating New Haven and New York styles in my home oven but that damn Napolitano style was another matter entirely, with its soft, charred (not burnt) crust and fresh, bright flavors. The kind Italians eat with knife and fork. If you know, you know. No way to cook one of those in my home oven without potentially burning the place down.

Last year, YouTube reignited the notion of building an oven capable of reaching the required temps with their 'quick and easy' perlite-cement ovens. Checking this forum on what the collective consciousness thought of the idea, I quickly dismissed it. Thank you! Digging a bit deeper here the homebrew castable method revealed itself and I was once again, back on a mission.

I read through dozens of build threads, took lots of notes and asked questions. I set about designing what I wanted out of this oven. My experiment with a dry-stacked firebrick oven taught me that I didn’t want a high mass oven that took ages to get up to temperature. Retained heat for bread baking also wasn’t a high priority. And I wanted it to look 'Pro' for all the B.S. my better half has put up with when I came up with an 'idea'. Since I wanted it primarily for pizza a lower dome for top radiation seemed important. Of course, david s and others quickly became a goto resource for many of the details and initially I really thought I could get by with a small oven. As I played around with design ideas and read more, it grew from a 26” interior to 32”. Perhaps small for some, but now that it’s built, it was the right call for my needs.

In the end, I tapped into so much great information here that provided a strong foundation and room for my own ideas. Thank you all. Particularly david s , Gulf, SableSprings, UtahBeehiver, bamforp, sergetania, loganc10, Nick J C , AndreasP and kebwi .

It’s now built, dried out and has a base stucco coat. I’ve fired it to temp (950+ dome) four times now over the last 3 weeks and while there’s still a lot to learn, my initial reaction is, Wow!

Here’s the first pizza. It’s a 63% hydration dough using Caputo 00 and natural leavening. When I took the first bite I was I transported to another time and place. That elusive soft and tender crust was within reach. An astute Italian would probably criticize it as 'measles pizza' and too pale, but as a starting point, I’m stoked.

This happened in 75 seconds.

[WaterDog]

Here’s how I got here. Keep in mind that there may be other ways to accomplish the same thing, but this is what I did. It was distilled down from this fabulous resource. Hopefully it will serve to help others to dive into a project like this. While I do have a fair amount of experience building (and destroying) stuff, this really doesn’t require many specialized tools or skills. Besides mixing concrete and knowing about hand tools, most of what I did here was my first time doing it. Be patient, don’t expect everything to go perfectly. You may very well end up enjoying the process, develop useful skills and have something very cool to show for it. My hope is that this inspires someone to take that leap.

The Foundation
I already had an 8x8 pressure treated base I built from my prior dry-stacked experiment. I made it over 10 years ago and while it may not be ideal (wood), it’s still super sturdy and square. Since this project was something of an experiment, I repurposed it. There are plenty of other threads here that cover the building of a proper cement block base.

I started by making a strong surface to build on. I poured a 2” thick concrete top in 3 sections using RapidSet Mortar cement with their plasticizer, similar to how you pour countertops. For reference see Michael Builds YT video. https://youtu.be/T7mYB6x68DY?si=0J7m3aWvzxn_9DB4 First time trying this but it was pretty straight forward and I’m pleased with the result. While I could have done this in one piece on the base, it was winter and I wanted to make some progress. The three pieces kept the weight manageable (approx 150 lbs ea) for 2 people to carry and the seams would mainly be covered by the oven. It also gave me time to create the live edge effect in the comfort of my shop. The products were purchased at Home Depot.

I planned it to be able to use one melamine mold for the three sections, and worked out the symmetry of the weep hole positions so I could pour 2 sections using the same hole layout. It’s easy to cover any holes drilled into the melamine using a packing tape patch. I used one sheet each of 3/4 and 1/8” melamine from HD.

As mentioned, the top has weep holes incorporated to encourage the large amount of moisture trapped in the insulation layers during construction to escape. By molding them in I saved a bunch of time having to drill them out afterwards. I used 1/2” galvanized bolts screwed into the 3/4 melamine, wrapped in packing tape and coated with WD 40 as a release agent. Worked like a charm. Once removed from the mold I created X channels for each weep hole using a grinder to further help any water find its way out.

The live edge on the countertop is created by using a 1/2” cold chisel and hammer. It’s surprisingly easy to chip off the edges of the concrete and it creates a nice look IMO. Initially I was going at it too aggressively and managed to whack off a corner. I epoxied it back on and call it 'character'.

[WaterDog]

The Floor Insulation Layer
Insulation for this project is all intended to help retain the heat that produced. It also functions as a heat stress protector which helps the heat diffuse and saturate through the refractory material while firing. Imagine hitting 900 degrees inside the cook chamber while the ambient air outside 2” away is freezing. Not going to end well. This can be accomplished by the use of rigid CalSil (calcium silicate board) which is a very good insulator for its thin size or by using an insulating material mixed in with Portland cement to act as a binder. Typical material for this is Perlite or Vermiculite. Their mixed forms are referred to as perlcrete or vermicrete on the forum. The insulating base also needs to have enough compressive strength to handle the weight of the oven.

I built a 2x4/melamine mold to create the mold shape. You’ll first need to work out all the details of your design before this step so you can position it accurately. Once it’s poured, it can’t (or shouldn’t), be moved. Details like the overall size of your dome, the size and shape of your chimney gallery and any decorative entry arch you plan on. Anything that would define the footprint of the whole oven. Theres a lot to account for here so double and triple check your dimensions. A drawing program like SketchUp comes in handy for this. I used Illustrator because that’s what I know. Of course, there’s no reason you can’t use pencil and paper.



I designed the under floor to extend past the oven dome exterior by 2 inches. That 2” will be filled by a ceramic blanket insulating step later

To help isolate the insulation layer and encourage water to exit I added a layer of mosaic tiles upside down over the countertop (not my idea) making sure there were channels between the tiles over each weep hole. Once that was done I added a layer of landscape fabric to prevent the perlcrete from clogging the channels. In the picture the tiles over the landscape fabric were only there temporarily to prevent the fabric from blowing away on a breezy day. BTW, I bought the mosaic tiles at HD. By rummaging around the tile area I was able to find these that were less than perfect and cheap to begin with, then then gave me 50% off for the damage. I think the cost per tile sheet was $1.50.



My insulation base is a combination of perlite and portland in a 5:1 ratio. I used 4 cu. ft. of Supreme extra course perlite from Amazon. I mixed in a wheelbarrow. First I mixed the dry ingredients and then water. Mix by hand with a hoe adding water as I went. It’s a funky mix. As you add water, the cement washes off the perlite, but keep mixing and it comes back together. I ended up using about 2.5 containers of water for every 10 containers of perlite. You’ll find water gets absorbed by the perlite so give it a little time to stabilize. No need to rush this. Eventually you'll end up with a loose mix of portland mud-coated perlite without any extra water pooling in the tub. Don’t mix too aggressively with any tools as you could breakdown the perlite and lower its insulating value. In the end I just used rubber-gloved hands to work the mix around.

Shovel the mix into your mold until it reaches the top. Screed off any excess to make it smooth and level as possible before covering it with plastic to dry for a day.

Give it 24 hrs to set before removing the mold. Then expose it to the sun and wind to dry. Remember all that water? Now we want to get rid of it. Protect it from rain or it will reabsorb water. Important to dry it as much as possible now before it gets covered by floor brick. I dried mine for 3 weeks.

There are a number of things you can do while the perlcrete dries. Layout and cut your floor bricks, gather filler for the sand form, build shape templates for the sand form and dome exterior, build a threaded rod support for the templates, build the oven mouth mold, build the chimney gallery mold, read about other forum builds again, figure out material quantities, source and purchase materials - masons sand, portland, lime, fire clay, burnout fibers, SS needles, ceramic blanket, etc., etc.

Didn’t take many pictures of this step but there are plenty in other builds.

[WaterDog]

The Firebrick Floor
I had firebrick left over from my dry stack project that I was able to use. My plan was to place the brick in a herringbone pattern because I like the look and it helps minimize your peel catching an edge. The brick needs to extend to the outside edge of the dome. The dome and chimney gallery will rest on the brick. I used my drawing program to figure out how best position the bricks to minimize the number of cuts and ensure I didn’t end up with too many very small pieces. From here I placed the brick in the pattern I wanted following a centerline taped onto the base. After determining the center point on the bricks I penciled out the dome/gallery footprint to ID where cuts were needed. I used a tile saw to make the cuts and placed each cut brick back on the base. Once I was satisfied with the final shape I numbered each brick and removed them to allow the base to continue drying. The rod/template can help here.

Here's a picture of the finished brick floor. Note the base is wider than the floor. That gap will be filled by the ceramic fiber layer.



Also shown is my template setup that will be used to define the shape of the sand mold and dome exterior. It's made in 2 pieces with a joint just below the sand surface so it can be removed prior to completing the dome casting. It’s also very useful to visualize what the interior shape of the oven will be and to define the dome footprint when marking floor brick for cutting. It was during this stage when I placed the template on the floor like the picture, that my dome height was probably too low so I redesigned it to be higher.

[WaterDog]

The Sand Mold
The purpose here is to build a sand mold defining the size and shape of your oven chamber. You’ll place the refractory homebrew cement over this mold so you want it to be smooth and dimensionally accurate. My dome height is 13-1/2” instead of a more typical hemisphere's 16”. There’s a lot of volume to fill so you want to gather up whatever you can to displace all that sand. I had more leftover firebrick and offcuts but even then I was shocked at how much sand I needed. 4 bags I think, maybe 5. At least it’s cheap.

I placed the threaded rod on the center point of the brick floor and placed bricks all around to anchor it, double checking it was plumb.



I continued to fill out the space with brick wherever I could using the shape template to ensure I didn’t get too close the edge. I then placed the oven mouth mold in position. The mold defines the oven opening as well as the mouth rebate. The rebate is where the door will be placed against to seal the cooking chamber after cooking to help retain heat. It needs to be flat and plumb. Using 1” rigid insulation foam for this was a real game changer. Another great idea found on this forum. Not only is it easy to cut and shape, it allows you to maintain a high degree of accuracy for your casting. It was this capability that ultimately had me trying something different for the chimney gallery which you’ll see later


Now start filling in the nooks and crannies with sand. I dumped the sand into a 5 gal bucket and added a couple handfuls of fire clay to help it hold together. I also used a spray bottle with water to keep it moist as I went along.



I used the template to define the shape and it worked out well. In the photo it’s easy to visualize how the mold will define the opening and rebate.



Once this was completed I set about further strengthening it by applying a papier-mâché layer on top. It was an insurance move as I was thinking about the placing of the homebrew over the sand, and having read reports of voids, I felt that a more rigid surface would allow a little more pressure to avoid them. It also helped lock the moisture in.

I cut strips of newspaper and made a mixture of 1 part water to .5 parts flour and .5 parts Elmer’s white glue. I ended up doing only two layers and when it dried it seemed super stiff thanks to the addition of the glue I suspect. Took a bit over an hour.

[WaterDog]

Casting the Dome
Using the latest homebrew castable formula, 3:1:1:.5 of mason’s sand, portland, hydrated lime and fire clay respectively, I set about casting the dome. I also added polypropylene burnout fibers and alkaline resistant (AR) fibers to help reduce cracking. I chose not to use SS needles.

This is another funky mix in that you want the right consistency to prevent slumping on the more vertical parts but not too dry where you’ll increase the odds of creating voids. I tried to follow the ball thrown in the air without coming apart test as well as the jiggle a ball in your open palm test for guidance. That said, there’s no doubt that experience matters most here. Unfortunately the most vertical sections are at the start so you’re tested right out of the gate.



I lightly sprayed the dome papier-mâché with WD40 to assist its removal. I then mixed up a batch of homebrew to see how the dispersal of the fibers went and to work out the consistency. Again, it’s easy to go too quickly here but you have time, it doesn’t set that quickly. Maybe 45 minutes or so depending on temperature.

I planned on working in 4-5” high rings. I found that placing the mix by rubber-gloved hand and jiggling it against the mold worked best. I then used a square metal trowel to work the mix onto the mold, smoothing as I went. I checked the shape with the template and added or subtracted as needed, blending with the trowel to maintain the 2” thickness.

One feature of my cast is the incorporation of a break at the top in an attempt to guide where inevitable cracking due to thermal expansion occurs. I stole this from one of bamforp build posts as it seemed to make sense and I couldn’t see a down side. I decided on a 22” diameter section on where to create the break. By defining the shape and placing newspaper over it, I then completed the rest of the dome, removing the threaded rod used for the template at the very end. The thinking is that this little gap would be enough to separate the two parts as the oven heated and create a crack along the break as normal thermal differentials occurred. Happy to report that in practice that’s exactly what happened.



At the oven opening I used the mold to make a smooth, flat rebate shape the thickness I wanted (1-1/2”) by using the trowel to follow the end plate shape. This was important because of how I planned on placing the chimney gallery.

I sprayed the completed casting with water then covered it in plastic to set up overnight.

[WaterDog]

Digging Out
After 24 hrs I uncovered the casting and set about removing the sand mold. The mouth mold was held together with coarse drywall screws so I simply had to take the screws out and pull out each 1” section at a time. The deeper sections didn’t come out easily so I used a drywall hand saw to cut them out. That left the sand and filler bricks.

Dug out the sand bit by bit and removed the bricks as I went. Pretty straightforward and uneventful.



That left the papier-mâché layer which I feared might be tedious. Turned out that once I got it started the whole layer was able to be removed in one piece, leaving no portions stuck to the casting. Easy, peasy. Phew! I attribute this to the WD40 and using the white glue in the mix.



Once the papier-mâché was removed I was able to take a look at how the casting went. Grabbed a flashlight and took a peek (it’s really dark in there!). Saw only one area at the far back that was bit rough but that was it. I felt no need to try and fill it.

The circular area at the top in the picture below is where the 'break' section is.



I placed a bowl of water inside the dome, sprayed water on the exterior for 7 days and kept it covered in plastic to cure.

It’s getting real now.

[WaterDog]

After 7 days I removed the water bowl and began the dry out process. To aid this, I placed a 75w incandescent floodlight inside the dome 24 hrs a day. Covered the dome with a tarp at night and removed it during day unless there was a threat of rain. This created a warm environment of around 150° to aid the drying.

[WaterDog]

The Chimney Gallery
I played around with the design of this for quite a while. Reading the forum brought 2 important points to consider, 1. A high funnel shape to aid the exhaust draw and 2. create as narrow a depth as possible to allow as much access into the oven when loading wood and working it. The narrow depth also helps how easily you can peer inside to see what’s going on.

It was recommended to use a 6” chimney flue for this 32” size so the overall depth of this section would need to be at least that. david s has a very good thread about this and his offset design that further narrows depth. A bit too complicated for a one-off but food for thought. As I was working out designs I had to consider how I was going to mount the flue to the gallery structure. I wanted to make the flue removable in order to make it easier to cover with a tarp when not in use. I ended up using a SS Duravent collar that the flue slides into. Works fine.

The typical placement of the gallery is to place it just in front of the oven mouth rebate, leaving a small gap to help prevent heat getting drawn from the dome to the cooler gallery.

Having worked with rigid foam insulation to make the oven opening, I was planning on using this method again for the casting of this section. Knowing that I didn’t want it to have the same 2” thickness as the dome and also seeing first hand how fickle the mix could be, I thought about the ability use the foam to build a completely enclosed mold where the homebrew mix would only have to be 'poured' in. That way I could control the thickness of the wall and make the fabrication a whole lot easier. I created a mock up and worked out how I could make this work. Having seen the potential of building up 1” foam sections, I settled on the idea of using aluminum flashing as the way to 'close in' the mold by screwing it to the foam mold end plates. Ending up with 1” thick walls.

A light bulb moment occurred while mocking up the concept. Because the foam mold allowed me to shape the inside and exterior of the mouth rebate with precision, I realized that instead of sitting in front of the rebate that I could design it to actually straddle it creating a nice transition for smoke to exit the mouth and head right up the chimney flue. This straddling setback would also reduce the depth by an inch which was not insignificant. The front end opening needed to be wider anyway to facilitate moving the door in and out. I was able to make the end that straddled the rebate and the front end the same shape. This design kept the depth to a svelte 7”. I would also leave a small gap where it straddled the rebate to prevent heat transfer which also had the auxiliary benefit of providing a vent directly to the chimney area to relieve any steam pressure created by water trapped in the insulating layers. I had not seen this done before but it seemed like a win-win to me.

I built out the full-sized mold and fitted the flashing to enclose it, using drywall screws. I mixed up the homebrew with fibers and cast into the mold using a trowel to place and then poking with a stick to prevent voids. I started with the flashing walls partially attached and screwed them to the mold as I made progress upward. The pictures show the completed cast in the mold as well as when I removed the end plates and aluminum side walls.



The aluminum 'walls' buckled a bit from the weight of the homebrew so the wall thickness got a bit larger than I wanted in places, but it held. I ended up grinding some of that excess off afterwards.

Here's a detail showing the gallery straddling the oven mouth.



All in all it worked great with a nice funnel shape with a smooth transition to the flue. Here are pictures showing how it sits over the rebate as well as an overall in position with the dome.

[WaterDog]

Decorative Arch
I made another mold to cast a decorative arch for the front. Used the same process as the countertops but incorporated some details including a faux keystone as well as mortar lines. Worked pretty well but I did make a mistake. I used the same ReadySet Mortar mix and plasticizer which is so easy to pour into the mold. Turns out it’s not rated for more than 200°. Oops, should used homebrew! So far it’s holding up but I only fired to temperature a few times. I colored it with Sakrete Terracotta powder.

[WaterDog]

The remainder of the build was pretty typical. 2” of ceramic fiber blanket. Chicken wire over that to act as a base for a 1-1/2” layer of leaner 10:1 perlcrete for more insulation and a 1/2” layer of stucco base coat to smooth over the perlcrete and make it look pretty. I did also add a 1/2” pipe fitting to place a vent at the top of the insulating perlcrete to help any steam escape. All of these steps are documented very well on other builds.



For the stucco base coat I used 1 part portland, 1/2 part lime & 4 parts sand. Trowelled it over the perlcrete and smoothed with the trowel and a green foam float leaving it intentionally rough so the final coat can grab on to something.

Here's a picture of what the 10:1 perlcrete insulating mix looks like.

[WaterDog]

After the base coat cured for a few days I began a week of drying fires following the standard protocol. Then larger fires and monitoring for steam for another week.

Feeling more confident, I built fires that cleared the dome, @850°+. All seemed good so I figured it was time to make pizza. Working the fire/coals around the floor to heat it and getting a good flame across the dome. It’s an interesting process taming this beast. Welders gloves are essential IMO. I can get it to clear the dome in an hour if I keep a big fire going but now I don’t feel this is good practice. A few cracks have developed. At the ceiling break where I expected one, at the far back of the oven up to the break (12 o'clock) and the latest on the right side (3 o’clock) up to the break. Nothing major. At times the dome has hit over 1,000° which at first I was excited about but now think I should slow it down a bit. With my next fire I’m going to concentrate on producing a good coal bed and feed in new wood more sparingly over time. This should help the oven saturate with heat better. I know its still retaining moisture and I need to temper expectations a bit.

This is where I’m at as of today. Hope it helps inspire someone reading this to take the leap. It’s a worthwhile endeavor. It does require some planning, patience and tenacity, but if you’re up for the challenge, your efforts will be rewarded. There’s nothing quite like cooking in an oven of your own making. I think it taps into centuries-old mojo.

I’ll add more thoughts as I gain experience. Thanks again to all on this invaluable resource.

Jeff

[bamforp]

That's a good looking oven - great work. I can confirm my oven has cracks in exactly the same places but they all stop at the break line rather than propagating a full 180° and none are big enough to give me any concerns.

I do have to move the coals around if I'm cooking pizza otherwise the floor temperature drops so in hindsight maybe I should have used some ceramic insulation board under the fire brick floor. Having said that we mostly use the oven for roasting and baking and for that it works really well.

[WaterDog]

A few other specs regarding the design:

Cooking Chamber - 32"d x 13.5" high - 41.5%

Oven Mouth - 8"h x 18" w - Opening to chamber height ratio 59.2%

None of these dimensions/ratios were chosen arbitrarily. Given its smallish size, and my performance intention, the dome height was determined by imagining the size of the fire I could realistically create as well as the desire to have the dome lower to the deck for top heat radiation. Obviously this was influenced by Naples pizza oven designs and modified for the size of this oven. I get a beautiful flame moving across the dome.

The opening to dome height departed from the classic 63% again due to size, purpose and practicality. Also the workability of loading wood stacks and moving peels in and out. It creates a very nice superheated air pocket between it and the top for doming pizzas.

Besides that, the shapes were decided by what looked attractive to my eye. In retrospect I probably would have allowed for a few more inches of straight side at floor level than I did but that's just splitting hairs.

[WaterDog]

Thanks again bamforp , I think your idea has a lot of merit. I've experienced the same thing with the floor temp dropping and am planning on the same method to try and recharge. It's still early days so hopefully that will improve over time. It's also why I mentioned slowing down the initial heat build up, letting those hot coals work the floor a bit longer. Easy to get the dome going with enough flame!