21" portable cast WFO

[SoCalZa]

Hi FB folks,

Long time lurker, first time poster. I've been interested in building an oven of my own for a few years and I'm ready to take a crack at it. I acknowledge I have zero experience with the materials and techniques, but I do love to make things, and I love to cook. I've sunk about 50-100 hours into these forums - you collectively have inspired me to take the plunge and build one of these things... Thank you to everyone for letting me learn from you, and thank you in advance for any constructive feedback on the below.

I am posting my plans here in the event you feel like sharing any feedback - I hope to avoid any egregious mistakes this way, so feel free so I can consider and address.

I credit WaterDog's build in 2024 as my main source of inspiration - I'll mostly be following this blueprint as it turned out fabulously and it all checks out with all the rest of the seasoned members of the community here.

Goal & purpose:
Cooking pizza for 1-10 people, with flexibility to cook steak on a Tuscan grill, slide in a chicken or loaf of bread, etc.

I need an oven on the small side so it's manageable in the limited space I have to work with, offers quicker fire times, and keeping in mind I am a novice, so approachability is a factor. I started out thinking I'd use fire bricks but pivoted to casting after considering feedback from members on time + experience, especially considering this needs to be a tighter build.

Considerations:
- I live about a half mile from the beach in southern California. Humidity is natural, if not constant, here.
- It needs to be portable. It'll rest on gravel in an uncovered, outdoor garden area. When in use, I'll pull it out a few feet to give some buffer between the oven + flue and the plants/trees. I do not anticipate being able to easily move this, but I need to be able to move it. When not in use, I'll cover with a weatherproof cover not unlike those on BBQs.


Design basics worth mentioning:

• 21" dome, cast with homebrew. Including burnout fibers to encourage evaporation.
• Weep holes drilled in the base refractory concrete (through the steel base).
• Steel frame with four pillars on caster wheels. Frame and caster wheels will be capable of supporting ~800 lbs; far more than I anticipate this weighing to air on the side of caution, and enhance mobility. I will coat the entire frame in Rust-Oleum.
• Frame is being custom built by a friend with a metal fab shop.
• Caster wheels: mounted to each of the four pillars, going with a 5" diameter solid rubber wheel. Considered pneumatics to aid mobility but decided against it as it adds complexity (murphy's law...). I may consider 6 wheels instead of 4.
• 5" stainless flue pipe, 4 feet in height.

Construction method:
Dome: I am purchasing the below plastic semi-sphere to use as my dome mold. Designed as a planter, if has an external diameter of 21" and height of 7.5". I will cast on top of this by hand (covering mold in saran wrap for easy removal). The flat base of the planter, which would form the dome, will be topped off with sand or other moldable material to give the top of the internal dome a uniform dome shape, and bring the ultimate interior dome height to 8".

I'll follow in WaterDog's footsteps by utilizing a rod through the roof of the mold with a template to ensure uniform wall thickness.



Flue gallery: I will create a mold out of wood to cast the gallery separately.

Floor: Fire brick in a herringbone pattern. I will cut the perimeter bricks with an angle grinder, knowing these do not need to be perfectly executed and will be enveloped by ceramic blanket + external layers.



Some open questions I am considering, which I'd welcome your thoughts on:

• 21" diameter x 8" height, with a door height of 7". This goes against the traditional ~66% principle, but I've read that's not necessarily gospel in practice from some of the senior members on this forum.
• A big design choice I'm mulling over, thinking creatively - what if I extended the dome height by establishing a perimeter of fire bricks (on their sides), and building the dome wall upon that? It would give me a height boost of 4.5". This would mean the dome perimeter is not perfectly round, but enables me to scale things up a bit, and allow for a door height in line with ~66%.
• Any tweaks you'd suggest given I'll be moving this several times a month about 2-3 feet back and forth over gravel?
• Should I consider 6 wheels instead of 4?

Three additional questions about the below illustration from DavidS on another thread last year:

1) Does it matter what material I use for the supporting slab? The slab will sit on the steel frame.
2) Can I get away with 3" of 5:1 vermicrete instead of 4 to cut weight?
3) I am projecting total wall thickness of 3.5 inches: 2 inch inner dome, 1 inch ceramic blanket + wiring, .5 inch for stucco. Does this sound about right?


If you've made it this far, thank you for your time.

[david s]

I see some problems with using the plastic planter dome in that it will be very difficult to cut away and remove out the oven mouth once the casting has set. I presume because of its size that the plastic is fairly thick. Also at 7.5 inches high it's not high enough IMO a hemisphere would be10.5" high, so the resulting decrease in volume is substantial. This might lead to an insufficient oven volume chamber for decent fire circulation (like removing one cylinder on a small four cylinder car engine). Do the math 4/3 x pi x r3.
Also the sand castle method is easier than you think. Although Waterdog used a template to create his hemispherical form it is not really needed. A stick in the middle of the sand castle of the length of yor desired internal height and a line pencilled around the perimeter on the brick floor is all you need to create a free form sand castle with surprising accuracy by just eyeballing the profile, it's really east.
The brick on edge idea to raise the dome height has the disadvantage of creating vertical joins at the base of the dome which is its most structurally weak point and at only 3' thick is inviting problems there. (a 3' thick brick dome has proved to be inadequate)

When you say "gravel surface, not sure how rough it is, but remeber that you'll have a high centre of gravity, so anything rougher than smooth concrete can become problematic, particularly with small wheels (eg think dangers of E scooters) Make sure your steel stand is fabricated from galvanised steel.

[david s]

If your plan was to cast the dome over the plastic planter, upend it to remove the planter then lift the casting and relocate it back over the brick floor, remember that it will be really heavy and moving it may damage it. It is easier to cast in situ.

[SoCalZa]

Many thanks for the quick, detailed responses DavidS. That is indeed what my plan was, and I'd enlist the help of a friend to assist with the heavy lift. I am more discouraged from this idea by the importance of proper height, than the weight while turning it over...

My initial design had a 10.5" height before I adopted the current idea of using the plastic mold, mostly driven by perceived ease of use. I see your point in your first note - the plastic mold-assisted design creates more problems and doesn't really solve what I hoped it would. I'll ditch the mold and use sand to get the ideal 10.5" height.

Confirming galvanized steel on the frame. Wheels will be solid rubber with tread, at least 8 inches in diameter. To make this all a bit easier, I'm now considering laying down pavers on top of the gravel to make the frequent 3-4 foot moves a breeze. The big wheels will someday serve their ultimate purpose when I move homes, getting into and out of a truck.