My first WFO design, any comments before I build?

[SableSprings]

I'll list a couple post threads below that will be helpful. The heat/flame from an active fire session is a large component of the top "heating element" for your pizza, however the radiated & stored heat from the refractory dome is a very significant contributor. Your basic design is good in concept...just the dome material & base structure need addressing. I'll put a link below to a nice illustration of a Pompeii oven cross section in the forum. Most casting is done with a sand inner mold that is covered with wet paper & lightly oiled to keep the homebrew from sticking. In general people find this method pretty straight forward and it works well. You can use an exercise ball, but you've got to figure out a way to support the "other half" from below...more work than it's worth (IMHO). A 4" perlite cement layer is very weak structurally. Many of us have used the 5:1 perlcrete underneath the oven floor bricks because that ratio will support the floor...but not much more...and it can be physically damaged very easily during construction. So yes, do look into a reinforced concrete hearth to support your oven.

Here's that nice, cross section illustration of a dome build:

https://community.fornobravo.com/forum/pizza-oven-design-and-installation/pompeii-oven-construction/406639-building-42-in-pompeii-any-pearls-regarding-laying-down-2-in-fb-board-beneath-firebr?p=406901#post406901

This is a great collection of well documented builds:

https://community.fornobravo.com/forum/good-background-information/newbie-forum/12621-a-newbie%C2%92s-survey-of-the-forno-bravo-treasures-hiding-in-the-archives

Here's a couple specific ones that deal with casting methods and often with comments from our "cast method expert" David S. (Most casting threads are in the Other Oven Types section/topics of the forum.) There are many well documented casting builds...these are just two I had in my notes and will get you started in the correct direction.

https://community.fornobravo.com/forum/pizza-oven-design-and-installation/other-oven-types/399040-cast-oven-build-in-shelbyville-ky

https://community.fornobravo.com/forum/pizza-oven-design-and-installation/pompeii-oven-construction/396954-longmont-co-new-wfo-build-casted-over-sand

Hope that all helps...keep researching and reading here...it's well worth your time to avoid build errors.

[Mark1986]

Hi Mike,

Thank you for your quick response!

Welcome Mark! We have had many builders try this method (perlite/concrete over exercise ball), but it has many problems. Primarily, perlite (and vermiculite) is normally used as an insulation and does not retain heat. It is also not even close to durable (crumbles/breaks easily). Casting an oven is a great building option, but using denser material such as refractory cement (expensive) or "homebrew" (3:1:1:1 - sand, cement, clay, & builders lime) is a much, much better option. There are many well documented builds in the forum that you should look at before continuing a build.

Can you tell me where I can find the well documented builds? I can't seem to find a topic or page dedicated to build plans.

Ok, so perlite and vermiculite insulate well but don't retain heat. Is the retained heat what cooks your food from above? If I would replace the inner dome material with refractory cement or homebrew, the problem in my design would be fixed? Can I still cast this material over an exercise ball?

A cast oven (2" thick) is normally done in sections because of the weight. The hearth needs to be able to support that weight as well. Wood bases such as in your design can work but the top slab is generally recommended as 4" thick reinforced concrete. A base barrier/drain system separates it from a layer of insulation such as CaSi board or 5:1 (perlcrete or vermicrete: cement). On top of that insulation lies your oven. Either ceramic batting or 10:1 insulating cement (again either perlite or vermiculite:cement) is recommended. Most builders apply a stucco type render over that outer layer as well as trying to waterproof as much as possible since most insulation materials will rapidly absorb water (making them useless as insulation).

Ok, so the 4" perlite cement layer I used is not strong enough to support the weight of the oven? I will look into using reinforced concrete then!

Also in your oven entry, you'll want to create a reveal. This allows you to seat a door so you can "seal" the oven for retained heat bakes such as bread or roasts (and many other things ). We're here to help you as much as possible based on lots of experience from the forum community... So again welcome & please invest time reading & learning through the experiences of other builders.

I still need to design the door reveal in Sketchup, will definitely include it! Thanks for your information and I am going to look into the build plans!

Cheers

[SableSprings]

Welcome Mark! We have had many builders try this method (perlite/concrete over exercise ball), but it has many problems. Primarily, perlite (and vermiculite) is normally used as an insulation and does not retain heat. It is also not even close to durable (crumbles/breaks easily). Casting an oven is a great building option, but using denser material such as refractory cement (expensive) or "homebrew" (3:1:1:1 - sand, cement, clay, & builders lime) is a much, much better option. There are many well documented builds in the forum that you should look at before continuing a build.

A cast oven (2" thick) is normally done in sections because of the weight. The hearth needs to be able to support that weight as well. Wood bases such as in your design can work but the top slab is generally recommended as 4" thick reinforced concrete. A base barrier/drain system separates it from a layer of insulation such as CaSi board or 5:1 (perlcrete or vermicrete: cement). On top of that insulation lies your oven. Either ceramic batting or 10:1 insulating cement (again either perlite or vermiculite:cement) is recommended. Most builders apply a stucco type render over that outer layer as well as trying to waterproof as much as possible since most insulation materials will rapidly absorb water (making them useless as insulation).

Also in your oven entry, you'll want to create a reveal. This allows you to seat a door so you can "seal" the oven for retained heat bakes such as bread or roasts (and many other things ). We're here to help you as much as possible based on lots of experience from the forum community... So again welcome & please invest time reading & learning through the experiences of other builders.

[Mark1986]

Hi all,

This is my first post on this forum, so forgive me if anything is off..

I got enthusiastic about building my own WFO in order to make the best pizza one can make. As I have financial constraints, I had to look for economic WFO designs. I decided to build one, casting over an exercise ball with perlite. It was quite hard finding all the build information in one place, so I gathered it as best as I can.

I am really fond of Sketchup, so I decided to model my build in it. Find the screenshots below.

It would really help me if someone could have a look at my design, and tell me:
1. If the design is good enough to work
2. Are the insulation layers of the dome and floor big enough?
3. Am I wasting any money on materials in my design?

Dome
4" perlite cement inner dome
4" insulation blanket
2" perlite cement render

Floor
2.4" fire brick
4" perlite cement

I am really looking forward to building my first WFO! Thanks in advance!

Cheers,


Mark