Homebrew Cast Oven Help

[watchthenanacrossing]

Hey y'all,

I'm just gonna ask some questions here instead of searching because that gets overwhelming for me instead of just direct answers. I'm starting my homebrew cast oven plans and need some help:

For the dome and insulating layers, I was thinking this set up:
Layer 1 - Sand, cement, hydrated lime, fireclay, fibers 3:1:1:1:1
Layer 2 - Vermicrete
Layer 3 - Ceramic blanket
Layer 4 - Another vermicrete layer
Layer 5 - Smooth finish (not sure of material but would like that look)

What thicknesses do I need for each layer?
What kind of fibers are best and how much?
Does there need to be a vent on the dome or will a flume at the top of the opening be okay?

As far as the insulating hearth, I'd like to use calsil instead of vermicrete because of time and easier to install. I already have the base and concrete slab up, so can it just sit on the concrete or should I use an adhesive? I want to double the floor insulation, so should I just stack two calsil boards on top of each other, or what would be a good way to achieve that?

These are just the beginning questions to get my plans rolling. Any input would be much help.

Thanks!

[david s]

There are a number of well documented home-brew cast builds that you should read. They will answer most of the questions you have. Unfortunately I am not organised enough to point you to them so if any other builders read this post please chime in. One build you can start with here.

#1 A bit old now but well documented.

Regarding your concrete supporting slab, you can do a little operation now that will greatly assist in water elimination. Firstly drill through the centre of the slab about three holes approx 1/2' hoping to dodge the red. Do this from underneath so when the drill blows out on the top side it will leave a divot to assist water drainage. glue som insect screen over these holes to prevent then try of insects. Then place some wall or floor tiles over the entire slab with sone decent gaps between them, it doesn't matter if some of the tiles are broken. What this will do is provide some pathways for moisture to escape at the same time as raise the calais slightly which reduces its tendency to suck up moisture that may have entered into the under floor insulation space. No need to glue any of the tiles or insulation down, gravity is quite sufficient.

For your dome layers do not add so much fibres The polypropylene burn out fibres need only be around a handful for every 10 lures (two gallons), but mixed in really well, they take a while to disperse properly, you don't want them clumping. The addition of stainless steel reinforcing is optional, expensive and makes the castable harder to work with so probably skip them. Layer 1 should be around 50mm(2") thick
Layer 2 Ceramic fibre blanket min 1"
Layer3 vermicrete min of 35mm 10:1 mix
Layer 4 render?stucco min10mm reinforced with either random mixed AR glass fibres or chicken wire.

Not sure on your reasoning for sandwitching the blanket.

[Gulf]

david s as always, has given you some great advice. I'll add this based on our past discussion. Linking back to your original thread. Though the pic is not of a cast oven, the basic theory is the same. You want the most effficient insulation nearest the cooking chamber. CalSil under the brick floor and cast dome. Ceramic fiber blanket around the dome. David gave you the minimum for that layer (the optimum is 3"). Not only is ist best as an insulution but, it also serves as an expansion joint between the dense dome material and the vermicrete layer.

Just adding this for you to also think about. Unless you are stuck on the appearance of an igloo, an enclosure wiil solve a lot of water intrusion and insulation issues.

[watchthenanacrossing]

I read through one guy's cast oven build, and he went with that layer set up. I thought it was overkill, but I thought I'd see thoughts on it. So, from my understanding is that I can get rid of that first vermicrete layer. It will go like this:
Casted dome (3")
Ceramic blanket (1 1/2-2")
Vermicrete (2")
Render (1")

Gulf Yes, I understood the diagram of your build. Firebrick floor and dome will be on the calsil, then the remaining insulation layers can be set on the concrete slab.

How should I approach the hearth? I'd like to use calsil instead of vermicrete, and I'd like the floor to be double insulated. Can two calsil boards go on top of each other?

I thought an enclosure oven was the same as an igloo?

[Gulf]

The joints/splices are staggered when doubling the layers of insulation board on the hearth. More insulation around the dome will also help with heat rentention.

Yes,technically, according to the Pizza oven Glossary an igloo is "A form of outdoor or indoor Pizza Oven enclosure where the exterior oven walls follow the basic shape of the oven chamber to form an Igloo, Dome, or Beehive. Also a traditional Mediterranean finish style." I should have used the term "doggie house" to describe a walled in gabled or hip roofed type of enclosure . Over the years the word "enclosure" has sort of evolved into being used to refer to the doggie house design.

[Gulf]

Also, please consider the advice from david s about "water elimination". It is important for an "enclosure" but, it is critical for an "igloo" imo.

[watchthenanacrossing]

This is all great stuff. It's really helping me out and guiding me by getting these direct answers. Two more questions to cover before I can start finding materials:

I plan on a 30" inner diameter oven based off of the supporting slab that is already in place. That will still give me plenty of room to build the dome and insulating layers to adequate thicknesses. The doorway will be 18" wide, 12" in height, and 9" depth. The inner height of the dome will be 16". Any problems with that?

I'm gonna go with a 4" thickness overall for the hearth underneath the floor with calsil boards. Should I still drill those holes on the slab underneath the hearth, or would the 4" of calsil take care of the moisture intrusion?

[david s]

First up, your door height should be 63% of internal height which is around 10” not 12”.
Secondly the calsil is very absorbent. So raising it off the floor reduces its tendency to mop up moisture as well as providing space and a pathway for allowing it to dry, should it get wet and it probably will. It also provides a decent pathway out of which the steam can escape. The underfloor moisture is the hardest to get rid of. So yes, still drill the holes and separate the slab fro the calsil with tiles.

[watchthenanacrossing]

Have you heard of this? I was pointed towards looking at these to use instead of calsil for affordability:

rockwool.com/products/co...loads#Overview

It sounds all good....water repellent, can stand high heat....but I'm not sure with the materials it's made of if it's good to put under the floor. Sounds like the strength of it might be an issue with the weight of the dome put on it.

[Gulf]

I clicked on the Rockwool link but, I didn't want any more cookies . However, I was able to see enough of the page to get the product name. Here is the Technical Data Sheet for Rockwool ComfortBoard 80. I don't have any experience with rockwool. But, I will put this TDS out there for the engineers to look at.

[UtahBeehiver]

This material is too soft, I believe I addressed to in another post. 439 (at 10% compression) "PSF" equates to 3.04 "PSI", Recommended compression strength at 5% should be around 75 "PSI"

[watchthenanacrossing]

Thanks, that's what I thought could be the issue with these boards.

[watchthenanacrossing]

I've decided to go the vermicrete route for the first 2" of floor insulation, and then I'll place calsil boards on top of that for the other 2" right underneath the firebricks. I can't afford for the floor to all be calsil boards.

Is 5:1 the correct ratio for vermiculite to portland? That's what I found in other forums.

[UtahBeehiver]

That will work, 5 to 1 by volume for floor and 8 to 10 to 1 for dome insulation for either perlite or vermiculite. Make sure domes walls also sit on insulation as well.

[watchthenanacrossing]

Okay, great. Could perlite be used instead of vermiculite for the hearth?