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New guy finishing outside of cast concrete oven

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  • New guy finishing outside of cast concrete oven

    Good morning,

    I purchased a 3-piece cast concrete oven that I will be installing in our backyard. My question is about installing the fieldstone on the exterior and the type of mortar that will need to be used.

    This is the oven that I bought and the description from the gentleman who makes them. “Three piece kit. Pieces can be moved by two or more strong people to get it set. Includes base and two piece dome. Base is made of UL food grade refractory cement. Dome is made of UL food grade insulated refractory cement. Inside cooking surface is 32 inches across, large enough for 2 pizzas at a time. It can be cooked in the way it is or finish it up with stucco, tile, brick or stone.” The picture is of his personal oven.
    Click image for larger version

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    I intend to install natural fieldstone veneer on the oven but want to use the correct mortar. The same fieldstone veneer is on our house, decorative posts, outdoor kitchen, firepit and will be done on the base for the pizza oven. We used standard Type S mortar in the past but need to make sure it will hold up to whatever heat will be transmitted through the dome of the oven. The gentleman who makes them states that the dome gets warm, you can put your hand on it, but not for too long. I don’t know what the temp actually is, but will Type S work or do I need to use something else?

    This is the base for the oven.

    Click image for larger version

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  • #2
    I suggest you ask the manufacturer on mortar for joints.. On another note, what are you planning to do for floor and dome insulation?
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    • #3
      He will supply me with refractory mortar to secure the 3 pieces together. In the past he has used 3M Fire Block sealant but now used mortar.

      Honestly, I hadn’t planned on any insulation for the dome sine it’s made from insulated refractory cement. The base will sit on fire bricks on my concrete countertop and be set in a wet bed of the same insulated refractory cement.


      • #4
        Then I think you need to do some research on floor and dome insulation. Both of these are key to a good performing oven. Download the free e-plans from Forno Bravo retail site and read them. Typically an insulating refractory mortar is not the main dome material rather a dense refractory mortar is used. There may be some issues with thermal mass and heat storage with insulated cement. You can also look at David S threads and posts, he is our cast expert. You can't have it both ways with one type of material (ie insulating vs dense).
        Last edited by UtahBeehiver; 09-28-2020, 04:23 PM.
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        • #5
          This type of oven is quite popular on the U.K. forum ,they seem to rely on the cooking base for mass and cool down quite quickly but many people seem to be buying them!


          • #6
            You are unlikely to get reasonable performance from the oven unless you insulate well both over and under the oven so it is totally encapsulated in insulation.
            large sections of dense refractory are subject to cracking from uneven thermal expansion, however this vulnerability is reduced by the addition of insulative aggregate in the mix.Unfortunately adding insulative aggregate also has the affect of drastically reducing the strength and durability of the casting, as well as reducing its thermal mass (heat storage capacity).
            The flue inside the chamber does provide a little more oven room but circulation is not as good as the independent front flue design, you will also need a valve in the flue pipe with this set up to control heat loss. Having built a couple of ovens of this design, (using dense castable though) I am familiar with their pros and cons. I concluded that the traditional front flue is a superior performer
            Kindled with zeal and fired with passion.


            • #7
              How would I go about insulating under the base? I plan to raise the entire oven up 6-8” off the concrete counter and can make any adjustments as I go. My plan was to put a layer of fire bricks under the base on top of concrete blocks. Will fire bricks add the insulating layer you talked about?

              I will speak with the gentleman who makes the cast pieces and see what his recommendation is with insulating the dome. We talked about using insulated concrete vs non-insulated, but to be honest, I don’t recall his explanation.

              More question to follow shortly.

              Thanks for the info gang.


              • #8
                Firebricks are not for insulation unless you use Insulated Fire Bricks aka IFBs.

                Again, I suggest you download the eplans from Forno Bravo, they go over various insulation scenarios and designs you can also look in the newbie section of the blog under Treasure Archives of some of the more documented builds.
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