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Homebrew cast oven build in Scotland

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  • #31
    Hi David and Al,

    Many thanks for your advice.

    I have a few more questions, and if its not too much to ask, could you tell me if I'm barking approximately up the right tree?

    First, is an insulated flu a good idea? I have a length of 900mm insulated flu - would this be suitable?

    I am planning to construct the oven around a piece of decking that is 1.8 x 1.5 m
    There will be six supports sunk into concrete to 40mm depth. I plan to use 150x50mm timber, doubled to make each support.
    I am aiming for the oven floor height to be 1m
    There will be a reinforced concrete slab with a layer of reflective building paper underneath, so that decking plus concrete is 100mm (decking approx 28mm) (, I have a roll of this)
    On top of this there will be a vermiculite concrete oven base layer 75mm thick
    Fire bricks 25mm thick.

    I then plan the oven dome to be cast (1:1:1:3) and 80mm thick, with a later of vermiculite concrete over this. I see that you had an additional layer of insulation, plus further vermiculite concrete and a render. I wondered is the fire blanket layer purely for additional insulation or does it also help with thermal expansion? Would a product like this be any good: (I have a few rolls already, would need to somehow prevent it being crushed). If not, how critical is this layer to overall thermal performance? Could I instead double the thickness of the vermiculite concrete layer?

    Is it a good idea to try to further insulate the oven base? It seems like detailing around edges will also be important to avoid thermal bridging, do you have any tips on good strategies?

    I will also follow your dimensions for entry, dome, and height. Seems like the dome dimensions to entry to flu is very important to achieve the correct amount of convection.

    Many thanks again, what a great forum! If I've missed information that is already here my apologies.


    Edit: I will use fine sand for the inner dome and course for the outer - if this is right!
    Last edited by Minnie; 04-01-2020, 06:09 AM.


    • #32
      Hi Minnie,

      I think the gurus Gulf & David S would ideal to give you an informative opinion. However, from what I have gathered from my sporadic reading on this informative forum is the following:

      - Double layered flue is ideal.

      - I would recommend a thicker insulation ( vermiculite concrete ) in excess of 100mm to 150mm providing the mix is 1;1:10 or 1;1:8 minimum. The thicker the better as concrete worst enemy is heat. Yes it is costly, but it is worth it, avoid cutting corners with building your oven. I would go for 150mm plus, better than regretting it!

      You can use Pumice but you can make the slab thicker.pumice is much cheaper.

      - VC FOIL ULTRA no harm in using it above the concrete under the insulation.

      - The loft insulation is not as efficient as the ceramic blanket, but if you have plenty of it, use it but the dome will be much thicker. remember every 1mm of ceramic blanket is worth at least 2mm of vermiculite/pumice or perlite worth of insulation.
      The more efficient insulation you have the better the oven maintains its heat. Although I did not appreciate this when I first started, but it turned out crucial for WFO (Wood fired oven).

      - If you build the oven, think of thermal bridges, this means that you need to think of how heat escapes from your oven through other materials to the outside and vise versa.

      - If you build an oven, think hard on how to insulate properly. Also, remember, the ore there are air pockets in your insulation, the better insulation is.

      - if you are driving anywhere near Woking or Chertsey in Surrey, I am happy to donate a cubic meter of pumice!! I live near Heathrow airport.

      - As for materials, always a good idea to check facebook Marketplace for firebricks

      Good luck and enjoy the terrifying oven thoughts you get on your pillow before you head to sleep!.....Be resilient to the demoralization you may start to face from family and friends half the way of your construction. be strong headed and keep on going. Mine took 4 years and it is not done yet!
      If you are starting to build your own oven, I recommend you start a new post so that your oven can be discussed in details freely without confusing posts.
      Last edited by Alomran; 04-03-2020, 05:38 PM.


      • #33
        Thanks Alomran! Yes I'll start a new thread, this has gone somewhat beyond "wow, and where did you get your stuff?"! I am in Scotland but thanks for the offer of pumice!

        Apologies Al for the hijack.