30" cast dome design

[hankplank]

hello sergentania, congratulations on your oven and thank you for sharing your pics and experience. your food looks amazing! I am currently in the middle of building a 31" dome with brick (which I will hopefully post about soon) and am very glad that you find your 30" big enough. As I'm painstakingly cutting bricks right now as I try a geodesic dome, I am very curious about what it would have been like if I had gone the fireclay homebrew cast route as you have done. do you have an idea as to the weight of your cast dome? do you know the heat retention ability of the oven for multi-day cooking? thanks again. I'm a first time poster but long time lurker and have learned much from this amazing forum. hopefully I can add something to it as well soon.

[sergetania]

Hankplank

Thank you and happy to hear someone finds my experience useful! As I was going through the build I was also thinking whether 30" is enough. Yes, definitely, for most home cooks cooking most foods. Honestly, I can't even imagine building an oven from bricks. That must be a lot of work but you will feel great looking at the completed dome. I never considered using bricks because I wanted to keep the weight down - after all the oven sits on a wooden stand. I wish I would still remember how much concrete I have spent for the dome. I think I have used 8 55-pound bags of castable concrete. The oven stays hot very long time. I never really needed it to but it keeps stored heat well and I only have a single layer stainless steel door with a fairly large oven entrance. Once I cooked a pork shoulder the next day after making pizza without making a fire. Of course, it drops faster when colder outside - one time I could not bake a pie next day after pizza but it was freezing, literally. Also, the oven gets hot very quickly so I don't hesitate using it for cooking because it is relatively easy.
Hope I have answered your questions. Best of luck with your build and start your build thread! I like seeing how others build and so do lots of folks here and that's how others can help.

[hankplank]

Hankplank

Thank you and happy to hear someone finds my experience useful! As I was going through the build I was also thinking whether 30" is enough. Yes, definitely, for most home cooks cooking most foods. Honestly, I can't even imagine building an oven from bricks. That must be a lot of work but you will feel great looking at the completed dome. I never considered using bricks because I wanted to keep the weight down - after all the oven sits on a wooden stand. I wish I would still remember how much concrete I have spent for the dome. I think I have used 8 55-pound bags of castable concrete. The oven stays hot very long time. I never really needed it to but it keeps stored heat well and I only have a single layer stainless steel door with a fairly large oven entrance. Once I cooked a pork shoulder the next day after making pizza without making a fire. Of course, it drops faster when colder outside - one time I could not bake a pie next day after pizza but it was freezing, literally. Also, the oven gets hot very quickly so I don't hesitate using it for cooking because it is relatively easy.
Hope I have answered your questions. Best of luck with your build and start your build thread! I like seeing how others build and so do lots of folks here and that's how others can help.

Ah I think I confused your build with another's who used the homebrew mortar to cast. but I see now you used castable refractory concrete which likely performs like firebrick. It seems your oven retains heat quite well. Glad to hear that you don't hesitate to use it as it heats quickly. I'm hoping I can get good usage too like I do currently with my Uuni Pro, which I fire up about two/three time a week.
I've been hesitant to post because I'm doing things a bit unconventionally but as I'm in a bit of a lull I will put a post together. I think you made the right decision not using bricks!

[sergetania]

I hope David or someone else knowledgeable may be able to correct me but I would expect a commercial castable behave rather close to homebrew. When I say the oven heats up quickly I mean probably one hour on average for general cooking (600-700F) and at least an hour and a half for pizza (800-900F).
Now, this is just my reaction to what you said, not trying to tell you what to do. I thought I was doing things unconventionally with the wooden stand. That's exactly the reason to ask opinion of experts here. I was so afraid to do something stupid to ruin long and fairly expensive build I wanted to make sure I was safe. Especially considering my total luck of experience working with these new for me materials. That was me, your situation may be different.

[hankplank]

May I ask the percentage of the alumina content of your castable? From what I've seen of the castables sold they are similar in alumina content and weight to firebrick (mine is low duty 20% alumina), and I thought I had read on the forum alumina content is a major consideration in heat resistance and retention ability. Just estimating but I think my dome will weigh about the same as yours, about 450 lbs. The homebrew recipe seems to me like it would have a lower alumina content because it is only one part fireclay.
I've never laid a brick or poured concrete before this project as well though so your point is taken and I will start a thread. And one hour to general cooking sounds great!

[sergetania]

I have used Harbison Walker KS-4Plus castable. You can look it up to see exact numbers but alumina content is 45%. Honestly, these numbers don't make much sense to me. I just used whatever I could get. Also, I think I have used only 7 bags, still have leftover bags in the garage.

[AndreasP]

sergetania , I really enjoyed reading through your build threat. I am currently planning a 32" oven using Homebrew. One question I am wondering about is the seize of the opening. I am trying to decide between 17" or 19" wide and 10" high. A shape similar to yours where the sides are vertical (8" tall) with a slight arch (2" in the center).

Did you keep the 19" opening width from your original plan?
How is the opening size working for you? Have you done any retained heat cooking like baking breads the next day?
If you did it again, would you keep this opening size of make it smaller?

Your input would really be appreciated.

[david s]

The larger the opening the greater the heat loss. On the other hand the larger the opening the better the access. Compromise somewhere between the two, depending on your priorities.

[sergetania]

Andreas

Thanks! I have kept all the sizes as I have originally planned. I don't see any disadvantages of having a wider entrance, quite the opposite. Heat retention is excellent, even the next day, in my opinion. I can easily move food inside even when I use two 12" cast iron frying pans and another smaller pan or two.

However, there's one thing that I would have tried to change if I am to build another oven. I get a lot of smoke out of the mouth of the oven. The oven is under a big tree and the chimney is only 2' tall so it doesn't draw smoke well. But my chimney opening is in the center of the gallery and doesn't extend to the sides. I wonder if I should have made the arch steeper and built in cavities to allow smoke be drawn into the chimney along the top of the gallery. I hope I am explaining it clearly. The main problem that I have is that the facade gets black every time I use the oven so I have to clean it to make it look nice. Not the end of the world but I would try to address it by redesigning the arch of the gallery.

Thanks!

[AndreasP]

Andreas
the chimney is only 2' tall so it doesn't draw smoke well. But my chimney opening is in the center of the gallery and doesn't extend to the sides.

I was planning on a 2ft tall chimney, but may just go with a 3'. I think you are talking about shaping the top of the gallery like a funnel to direct the smoke into the chimney. I will try to do that to help with the draft.

As for the opening, I may just go with 18", maybe that's a good compromise. I certainly want to do retained heat cooking / baking, so heat retention is important to me.

[sergetania]

Andreas

Look for gallery pictures David posted to get the idea. I am sure his design is rather optimal. Also, I am sure my smoke draft problem is made worse by the tree canopies above the oven.

I am not sure how much an inch or two of the entrance width matter when it comes to heat retention. I probably worried about it too much but then the results exceeded my expectations. If built right it is amazing how well the insulation stores hear.

I cut the shape of the oven floor using the exact dimensions out of a carton box to understand what can fit in the oven. It did help me.

[AndreasP]

Thanks, yes, I have looked at photos and many posts. I think I have the smoke collection part figured out. I am with you on worrying about details (and maybe too much). After all I am not planning on building another oven, so I want this one to be as perfect as it can be.

I had some old 1/4" hardboard from drawer bottoms and drew all the sizes on that one. I am building the oven in a corner, have limited space and only have access from one side, so it helped a lot.

Thanks again for your comments! It is amazing how much support I get from people on this forum !