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The most definitive and incomplete guide on sub floor building

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  • The most definitive and incomplete guide on sub floor building

    I’ve been absorbing (pun intended) floor insulation methods. Since starting my learning 5 days ago, I consider myself and expert and would like to share my knowledge.

    Joking aside this is a living post. I will edit often and save in my bookmarks. I am using this for my own personal reference while providing easy to read information for everyone.

    Please feel free to chime in with you thoughts and research. I will update the main post.

    Why subfloor:

    The subfloor of a pizza oven is often dismissed as a non essential cost. Most of us start with a small budget. Speaking of budget… The stupid pizza oven bricks are $2-$4 bucks each and I need 200 of them. How much is this slice of finished pizza going to cost me?

    Don’t fret, budget is irrelevant when you imagine a finished wood fired pizza borne from the mouth of a smoldering oven. An oven you made from your own hard work and fortitude. The pizza is a work of art and taste better than anything ever was and ever will be. Friends and family rejoice your name.

    The insulation of subfloor is important reduce fuel burn ( wood ) and retain heat. The more heat you retain, the less fuel and more even cooking times. A configuration of refractory brick placed on a cement slab will add to the total thermal mass. If the fire facing side of brick is 500F the other side of firebrick is 400F touching the cement slab. A giant heat sync effect is created. Pulling heat away from your oven into your cement slab. You will be throwing wood into your oven like a coal powered train going 80 mph. Well not exactly but baking bread and long cooking will be labor intensive when checking temp and adding fuel. Getting the oven up to a hot 800F cooking temp for great pizzas will be longer when your heating 1000s of pounds of concrete below the oven.

    We have the technology:
    Two camps:

    The rich: (Business owners, Doctors who ride Harleys, Retired Folks, Architects

    They use Calcium Silicate board (CalSil) . High Tech 2” min

    The poor: (Blue collar workers, Plumbers, Weekend warriors, Young families)
    They use Vermiculate / Portland cement mix. Low Tech 4” min

    Common Floor Configurations (TOP TO BOTTOM)

    Config 1:

    Config 2:
    Vermiculate/Portland Mix 4”

    1. Vermiculate / Portland Cement Mix Ratio thanks to UtahBeehiver (5 to 1 under floor and 8-10 to 1 on dome, min 4" under floor and dome. ). Click image for larger version  Name:	image_87621.jpg Views:	0 Size:	150.8 KB ID:	420624
    2. Estimate for Thermo 12 Gold Cal Sil product board $224. E-Order 2991590-00.pdf
    3. Thermo 12 Gold spec sheet. IND-300-Thermo-12-Gold (1).pdf
    Attached Files
    Last edited by stevef22; 04-03-2020, 06:30 PM.

  • #2
    I'm at the point of beginning to build the oven floor on the concrete slab. My initial thought was to use the calsil pad, but it was recommended to me to use 2 courses of firebrick instead as the calsil tends to compact over time. Is this true and if so will that render it less effective over time?
    My current thought is to do one of two options. I'll use the above outline to describe them

    Config 1 (top to bottom):
    Cement slab

    Config 2
    2" vermiculite/portland mortar mix
    cement slab

    Config 3 (original plan)
    Calsil 2" Board
    Cement slab

    I am looking to build the best insulating scenario. Would one of the above be adequate? Or should I consider the following:

    calsil Board 2"
    Vermiculite mix 2"
    Cement slab

    Thank you. This forum is a tremendous resource.


    • #3
      Good question... what about foam glas block? I like your last thought just off my limited research.


      • #4
        That IS a good question. I'm in a similar situation. Did you make a descision on your config?


        • #5
          In The Middle of the Pizza Oven area (Only) !! 40" Inside Dia. Build

          Holding up the Center of the 6" Concrete floor will be Cement Board formed tight to each of all (4) sides of edge of forms. 2"x4"s & 8' will hold the middle & underneath of the Cement board.

          After This:
          The Middle / Center section will be formed & 6" lower to accomidate the thicker insulated floor area ?


          I'm using 4" Thick 50/50 mix of Vermiculite/ Perlite mixed, with Portland Cement, & Sand,= (1) Part Part Portland,(2) Parts Sand. (3) Parts Vermiculite.. {Filling in the Middle Area Only}.

          After drying. I'm covering the mix with Aluminum Tin Foil. This will be overlapped around all ends. To keep out any moistures from going up into the ceramic board..

          Take the forms off & pour the outside with solid concrete, to fill the rest of your outer area. My Total area will be 7' x 7' Square.

          I'm adding a 2" Thick
          Ceramic Fiber Insulation Board (2300F) (1.6" X 19.7" X 39.4") Thermal Insulation. Bending up the Foil around all the ends & over the Board, to keep moisture out !

          The Board gets cut into shape of 40" Round Dia. Both the Oven & Front Opening of Oven Area.

          The Fire brick get laid out, leveled, & cut into, a Herringbone pattern.

          A soldier course of Standing Firebricks are next, etc..


          • #6
            What is the reasoning for 4" 3:2:1? It offers very little insulation value. If you look at a couple posts earlier you will see a table showing a K value of 2.5-2.75. A 5 to 1 ratio is sufficient for under the floor and dome and has much better K values. "SKIP" the foil, it will also keep water in, and it will get in. Having a sunken insulation pit is like a catch basin for water to sit. Wet insulation is one of the most common reasons for poor oven performance. Add weep holes under the floor area. Be aware that a full standing soldier course may require buttressing due to the outward forces on the dome at the joint. I suggest you set back a step and get some of these issues sorted and researched out.
            Last edited by UtahBeehiver; 08-23-2021, 07:19 AM.
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