Questions for my first cast oven build

[david876534]

Hello All!

First post here. I am planning on building my first oven and wanted to ask some questions here. I've heard there's a couple of cast oven experts on this forum!

At a high level: I plan on casting the dome with refractory cement and using vcrete over that (maybe pcrete). I'll probably go with sand (it seems to be a better approach than big exercise ball but still undecided) to make the mold to lay the cement over.
Currently I have a lot of red clay brick hanging around so that's the reason a lot of it is used for the base/decoration.
My current plan is to:

(For the base)

• Create a 6" thick foundation (5'x6') out of Portland cement (reinforced with rebar)
• Lay brick on top to make the fuel storage area (dimensions in photo)

(For the cooking surface/dome)

• Create a 6" Portland cement surface (5'x6') on top of the brick base, leaving a 4" deep mold in the middle (in the shape of the dome + opening)
• Fill 2" of 5:1 vcrete in the center area when the cement dries, and then a 2" of fire brick on top of that.
• Create the 41" sand dome on top of the firebrick and cover with 2" of refractory cement (leaving room for an 18" wide opening)
• Once that dries, I'll put a 3" layer of 10:1 vcrete over it.
• cover that all in decorative 1" thick red brick slices.

Immediate things that come to mind:
I planned on putting the firebrick flush with the top surface, is that a problem? Should it be a layer on top of the upper cement surface?
I've heard mention of not mortaring the firebrick for the cooking surface down, is that the right thing to do?
Is a 6" thick foundation/base thick enough to support this all?
Are the brick walls (5" or so thick) strong enough to support the top?
Is the 3" layer of vcrete enough to insulate a beginner oven?

Any other comments are welcome too, I'd really like to get this right! Thanks in advance!!

[david s]

The heavy dome and floor will be supported by only 2” concrete. I think that is inadequate. Normally the oven sits on a 4” reinforced slab.
Your stand looks a bit high too, normally it’s recommended to be at elbow or belly button height. Floor insulation if using 5:1 vermicrete needs to be at least 3”, normally 4”. If using calcium silicate board you can halve this thickness. If using 1 0:1 vermicrete for insulating over the dome again, 3” minimum 4” better. There is a problem in using vermicrete directly against the inner casting and that is the sudden heat hitting wet vermicrete can causes steam and can make it swell and crack, particularly when first driving off the water. A layer of blanket, being already dry, over the inner casting and under a layer of vermicrete reduces this problem and the blanket can also act as an expansion joint.
Floor bricks are better left laid loose so they can expand independently.Also should any deteriorate in the centre, they can be easily replaced.

[FireFood]

Hey dude, the ovens I have made from refractory cement always have had 4 or 5" thickness and they have worked well. If you think of the process of packing refractory cement around the sand form you can imagine it will be tough to pack the cement in just 2" layers. Also, the door way which is always a weak spot and possibly the whole oven, might not be structurally stable with just 2" of refractory.

For insulation - thicker is better but if you want to minimize the material thickness the oven will still work well, it just may not hold heat as long, depends what you want to use it for. If it is just for live flame cooking of pizza then it would be fine, but for baking and roasting maybe not.

Hope this helps!

[david876534]

To the first point, So I could leave only a 2" layer open for the insulation in the slab, use the FB insulation board, and set the firebrick on top of that then?
Does the board need to be mortared in to place or anything?

Next, I'm going to push back about stand height - 4 feet (6" slab + 3'6" stand) doesn't quite hit my belly button with a 37" inseam haha.
(although the two other guys I live with are only 5'11" so maybe I'll be nice and drop it a few inches)

Then, as far as the blanket I assume you mean the FB insulation blanket? If I were to do a 1" thick blanket over the dome could I then cut the Vcrete down to 2" over that?

Thanks so much for all the information I really appreciate it!

[david876534]

Hey dude, the ovens I have made from refractory cement always have had 4 or 5" thickness and they have worked well. If you think of the process of packing refractory cement around the sand form you can imagine it will be tough to pack the cement in just 2" layers. Also, the door way which is always a weak spot and possibly the whole oven, might not be structurally stable with just 2" of refractory.

For insulation - thicker is better but if you want to minimize the material thickness the oven will still work well, it just may not hold heat as long, depends what you want to use it for. If it is just for live flame cooking of pizza then it would be fine, but for baking and roasting maybe not.

Hope this helps!

Sorry, saw this after I replied to david s, so the 2" you believe won't be strong enough? Is there anyway I can improve the strength of the refractory without hurting the... refractory part of it? haha.
Yeah, I was thinking about beefing up at the doorway although I'm still pretty out of sorts as far as what to do when it comes to the entry point.

If I can get away with the 1" blanket and 2" of vcrete hopefully that would be fine.

[david s]

Most cast oven manufactured ovens are around 2” inches thick and unreinforced. If it proved inadequate they’d be inundated with warranty claims. You can enhance the strength by adding 2-4% random stainless steel fibres.
http://www.palmertechgroup.com/resea...s-steel-fiber/

[Bricklife]

Hello All fellow wood fire enthusiasts.

I am doing my first wood fired oven.
Still a lot of work to do, but I have really enjoyed this project.
Excited about the build and waiting for the cooking.

Question for the experienced builders here:
I got large amount of Firebricks and build the bottom table from them too. Just wondering what kind of paint could be used for them. The idea is to paint the bricks and the concrete with same color (white).

Thank you for your help,

[UtahBeehiver]

Any good quality exterior paint would do. I do have have a question, what material is under your floor fire brick, is it a perlite or vermiculate/portland mix and what ratio did you use? If you used a straight concrete mix then you need to step back since a straight concrete mix will act as a heat sink from the fire brick affecting the floor temperature of the oven.