Homebrew castable oven planning

[ebbbe]

Hello,

I am in the lucky situation that I will have a lot of free time on my hands in this coming summer so this will be the year that I will build a pizza oven. Finally.

As I do not currently own the house I'm living in (something I have seen other people mention in this part of the forno bravo forums) I might be required to move the oven at some point. This will not be for several years and it will only be one time. Still, it means that I will not be building a Pompeii style brick oven. I have set the following design requirements in mind that I think (hope) are feasible:

• The base will be a sturdy wooden table with a concrete table top.
  • No wheels. They seem to be really expensive with the weight they have to carry.
• The oven size will be 70-75 cm inner diameter.
• The dome will be made from 3:1:1:1 homebrew with a thickness around 5-7 cm
  • Burnout pp fibers will be added I think.
  • No SS needles - I cant find a supplier where I can buy less than 25kg
• Below the oven floor I will either insulate with 10 cm perlcrete or some sort of insulating ceramic material.

I have not completely decided whether I will insulate with perlcrete (5-10 cm) or ceramic blanket (5 cm), but It'll probably end up being the former due to cost.

My main inspiration is the oven built in the thread below:
https://community.fornobravo.com/for...ent-oven-build

I have couple of questions:

1. I am wondering if i should change the recipe for the homebrew for the following reasons:
   1. Lime - As I understand it the type of lime that is used in the homebrew recipe is hydrated lime Ca(OH)2. I have only found one place where I'm able to get that, but at a very high price. In fact it is almost as expensive as the source I have found for hydraulic lime NHL3.5 (CaO). From this thread (https://community.fornobravo.com/for...-hydrated-lime) Post #10 it seems that hydraulic lime is better for the purpose that hydrated lime? Is that correct or do I completely misunderstand the thread?
   2. Cement - I cant find high alumina cement at a reasonable price. I've found one supplier with a crazy price and high shipping costs.
      
      Would it be preferable to use skip the portland and make a mix of sand, fireclay and hydraulic lime in a ratio of 3:1:1 ?
2. Do the sand need to be of a particular grade or type?
3. I can't seem to find the density of cured homebrew. Is there an estimate to this so I can estimate the final weight of the oven?
4. How to I determine how much of each component I need?
5. Have you guys heard of insulating firebricks? The website where I can get lime, clay and firebricks sells these. Can they be used for insulation under the floor or do I need the ceramic board or perlcrete for that? (link in danish: https://www.ildfastesten.dk/ildfaste...n_300x300x50mm)

Thanks in advance!

Best regards
ebbbe

[david s]

Hi Ebbbe,

1. Try doing more searching. Hydrated lime is commonly used by bricklayers to improve the consistency of the mortar. Don't skip the portland cement. The alternative calcium aluminate cement is expensive and is harder to work with as it sets extremely quickly. Adding lime to it accelerates the setting time even further so stick to the home-brew recipe.
2. Any sand should be ok but some that has a variety of grain size is better.
3. Density will be around 1.8 kg/litre
4. The 3:1;1;1 recipe is by volume. The volume of a sphere is 4/3 pi x r x r x r (divide this by 2 to get a hemisphere) calculate outer volume and deduct inner volume to get volume of the inner shell
5. Insulating fire bricks make great under floor insulation but are usually way more expensive than vermicrete.

[ebbbe]

Hi David,

Thanks for the fast reply.

1. I'll keept the recipe as it is then. I did read on a site you linked in another thread that hydraulic lime can be used together or instead of hydrated lime, although they were not talking about using it as a refractory material. So just to be completely clear, is it not worth it to use hydraulic lime in the homebrew recipe? Or would it in fact make it worse?

4. What I ment with my question was if the volume of the product was different than that of the sum of the reactants, but you answer clears that up as well.

5. Allright. I was thinking it was also easier than casting a perlcrete base. Lecablocks might be easy and they are cheap. Would that work?

Thanks!

[david s]

Hydraulic lime would be best. If it were available to me I would use it. I can get it but it’s cost is prohibitive, so I use hydrated lime which is commonly used here and cheap.
Leca blocks sound like a good alternative to vermiculite or perlite if you can get them cheaply, but make sure they are very light. The denser they are the poorer insulators they make. The beauty of using precast blocks is that they are already dry and you won’t have to worry about drying them as you do with a cast vermicrete or perlcrete slab.
I’ve used Leca (lightweight expanded clay aggregate) in castings that I want to be strong yet lightweight and insulating. Because each little ball has a strong exterior but softer and lighter centre it creates both strength and lighter weight in the cast product.