New Castable Home Brew Oven

[geoff7877]

Hi everyone-

I started a thread here last week, https://community.fornobravo.com/for...w-cast-rebuild which has lead me here. My old oven is still performing great, but I think at this point, the dome design is the only thing holding it together. I can literally see daylight through the large crack in the back, through the mouth of the oven. There’s also a large piece in the back of the dome that you can wiggle slightly. Not good.

I will be building the new oven in place, on top of my block island that I’m currently in the process of building. Cost is definitely a factor here. After the expense of building the island, building a new pizza oven was not in the plan, but here we are…

Here are my thoughts at this point:

Castable home brew dome placed on a perlicrete 5:1 base topped with firebrick. I’d like to build expansion joints into this oven, so I’m thinking of casting this into thirds. One third being the front with the register and the other two thirds would be the back of the dome split down the middle if that makes sense. Kind of like a peace sign.

I’m considering building the register out of fire brick and casting the front of the dome over the back of the register to join them together. Have not quite figured out any advantages or disadvantages of a brick register vs a cast register.

As for the form, I thought about sand cast, but instead of spending the $$ on 200 pounds of sand, I’m thinking of using the same method that I used for my current oven. I used a gym ball, but wrapped half of it with cloth plaster strips and made a half dome shell. Worked great and was cheap.

Being this is not a planned build, I would love any advice. I’m going to build this to the same specs as my current oven since the island was built with the current dimensions. Inside diameter is 26” but it’s a functional size for my small family.

Thanks in advance

[WaterDog]

Greetings geoff7877 I’m currently in the middle of my cast build having completed the base insulation, firebrick floor, dome and flue gallery. I’ve spent a considerable amount of time scouring this forum for best practices and ideas. Not sure how up to speed you are on the castable recipe but it’s now 3:1:1:0.5 (Sand, Portland, lime, clay) along with polypropylene fibers to help prevent spalling, alkaline resistant fibers for strength as well as SS needles to also increase structural integrity and prevent cracking. These additional fibers are considered essential but do increase costs somewhat. For my build I decided to use only the poly and AR fibers, not the SS needles.

As far as the build in multiple pieces, I think you’re going to find that in order to accomplish what you intend that you’d have to build a mold. It’s been done, but for a one-off it would really be time consuming and expensive. If your primary concern is manageable pieces for transport that approach would make sense. If it’s to minimize cracking, I believe there are other factors to consider. Castables crack, it appears to be a common issue, but the extent of the cracking and how it affects oven performance seem insignificant for most. While I can’t speak to my experience yet, I am taking the time for my casting to dry out as much as possible. I’ve also incorporated a recent idea to try and control where the oven cracks by incorporating a break in the cast by using newspaper. The idea comes from this bamforp thread https://community.fornobravo.com/for...562#post447562 Post #19.

I can’t speak to the use of bricks for the flue gallery but I believe there are examples of this. I recall a hybrid with brick sides and a cast flue section. I cast mine using 1” rigid insulation to create a mold. The use of this material really opened up possibilities because it’s easy to cut and shape, helps you visualize the final piece and is relatively cheap ($25 for 4x8 sheet.

Hope this helps. Happy to share what I know even though I’m certainly no expert. Attached is a picture of where I’m currently at in the process.

[geoff7877]

WaterDog Thats amazing! Do you have a thread for your build? I’d love to check it out.

My thought behind creating this in sections was to help control where the cracks are instead of having it crack and letting it just run its course. I know it will crack for sure. Just trying at least feel like I can manage some of the cracks. Give them a path to follow. I saw the post you’re referring to with using newspaper to create some separation. That’s more of what I had in mind.

Looks like your base is a perlicrete or vermicrete mix?

Beautiful oven man. Thanks for your input. It’s greatly appreciated.

[WaterDog]

The base is 5:1 Perlcrete. It's placed on top of ceramic tile which acts as a mesh to allow residual moisture to escape out holes placed in the concrete countertop.

In that thread you probably read david s reply referencing his oven and the crack locations. If you use this newspaper preemptive approach perhaps that will give you placement ideas. David certainly has the most experience with this type of build and I’ve learned a ton by reading his replies. Since I’m doing a lower profile dome shape I created that break at the top ilike bamforp did in a 21” diameter circle. We’ll have to see in practice how that works out. BTW my oven is 32” diam.

No build thread yet but I have been taking pictures so may put something together. Thanks for the compliment.

[bamforp]

geoff7877 - regarding formwork for the dome, by using some old bricks to make up the bulk of the volume of the dome, I found I could reuse most of the coarse sand from the dome formwork in the flue casting such that there was very little waste. The nice thing about a cast flue/register is that it's very easy to seamlessly link the dome and flue. I haven't built a brick register but I could imagine it's a bit more challenging to create a seamless connection. In practice, I haven't seen any disadvantage to having a cast flue - it runs a lot cooler than the dome so I think the only reason to use firebrick would be for the aesthetic.

[geoff7877]

bamforp Great point about re-using the sand. I’m literally starting from zero planning so I appreciate the input. I’m still trying to find the right materials to use locally. You mentioned course sand and I realize that may be something different in the US. I just want to make sure I’m looking for the right materials. I’ve located everything else.

I was also looking for a materials calculator but have not been able to find that yet. I’m sure that exists somewhere on this forum.

Regarding the fire brick register, I’m not married to the idea vs casting a register. I did a dry fit yesterday with some fire brick I have for the island. They’re about 1/3 bigger than a standard brick and I think aesthetically, it would not look right with this size oven. With that said, what are the advantages of casting the register separate of the oven a joining the two together? I get the separate cast like WaterDog ’s register. Initially, I’m thinking of creating the same shape as my existing register, which is pretty basic. I cast the dome and register in one cast. It has worked great. My big mistake was that I cemented my flue in (with perlicrete) and first time the flue got hit enough, it cracked the register which carried into the dome. So, with that, I may have just answered my own question regarding a single cast vs two separate casts, mortared together. I will also have to allow room for the flue to expand this time around.

[bamforp]

Coarse sand (or often called sharp sand) on this side of the pond is typically the sand you would mix with aggregate and cement to make concrete.

A big factor for me choosing to cast the flue after the dome is that it is very easy to have the flue sitting partially over the front of the dome thereby minimising the footprint of the oven which was important for me. A shallow flue also makes it a little easier to work the oven.

[WaterDog]

I also cast my gallery to minimize the opening depth. Using foam molds for the oven mouth and flue gallery helped make this possible and more precise. The gallery sits over the oven mouth by an inch. I left a small gap to isolate the dome itself and to provide an escape for any pressure build up. I also plan on incorporating a small vent at the top of the dome insulation as an outlet for steam to escape.