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Foundation Slab

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  • Foundation Slab

    Yesterday I poured the foundation slab for the Pompeii Oven. I want the overall oven in the end to be 36".

    Anyway, I poured the slab 45" x 4'. It is going to be integrated into a kitchen outdoor island that we poured the foundation for yesterday that is shaped as an "L" and the oven is going to be in the elbow of the "L". Do you think this slab is much to small? Or do you think I can leave it as is and just make sure when I pour the base of the oven that that is a bit larger or will it not be safe?

    If you click the link below you will be able to see what we have done to get a better idea.

    Pizza Oven Foundation

  • #2
    It's way too small.

    You're leaving no room to account for the insulation or covering on the dome.

    It should be at least 6 feet wide by 8 feet deep. Otherwise, you've got no room for the insulation, landing, vent or door.

    I just completed building a 35" oven. My slab was 60 X 72. I wish I had gone bigger.

    Before you get too far along, enlarge your slab.
    There is nothing quite so satisfying as drinking a cold beer, while tending a hot fire, in an oven that you built yourself, and making the best pizza that your friends have ever had.


    • #3
      reduced base size

      I don't know how you are going to finish the oven, but there is no particular reason you couldn't use your base as a pedestal, and pour a larger hearth slab on top of it. This would reduce your firewood storage, but not by much.

      After all, much of the weight is in the center of the slab, not at the edge unless you build a massive enclosure.
      My geodesic oven project: part 1, part 2


      • #4
        Dmun, Thank you that is exactly what I was wondering. I am so relieved to hear that most of the weight is set on the center.

        Thanks again!


        • #5
          Stand size

          Hello Ryan,

          Putting a 36" (internal) oven on a 45"x48" stand won't fit.

          Counting sideways you have roughly:

          36" oven
          9" oven walls
          10" insulation
          2" enclosure walls

          57" wide

          You can tinker with that by minimizing your oven wall width, using more efficient insulation (all Insulfrax for example), and making thin upper walls. Or as David noted, you can cantilever your hearth slab. But fundamentally, you need each of these functions.

          Once you have your oven footprint done, you can add other outdoor kitchen elements with either block or metal stud "cabintets".

          There is posting on stand size that might help.

          Pizza Ovens
          Outdoor Fireplaces


          • #6
            I understand that the oven itself won't fit with all the layers going into it, but this base is just to store wood and later on I will put a larger slab on it once built up. I just was wondering when I start constructing this if this base can support a larger slab (the hearth foundation) which will be the correct dimensions. My only question is will this base be strong enough to support a larger base about 3 feet in the air supported by the cinder blocks and obvioulsy rebar in the second slab. I want the pedastal part of the oven (where I am storing the wood to burn) to be smaller. so it it cohesive with the island as a whole. I pretty much am looking for in the end to see the kitchen island with a large box sitting on the "elbow" of the "L".

            Dmun explained just what I needed by telling me that the weight sits primarily in the middle.


            • #7
              Yep, I think you are fine. You will cantilever the hearth over the stand on both sides, but with a rebar slab, you can span that distance. That, and as David noted, most of oven weight will be over the stand --it's the insulation layers and the enclosure wall that are at the outer edge of the hearth.
              Pizza Ovens
              Outdoor Fireplaces


              • #8
                Wonderful thank you everyone for your help!


                • #9
                  Oops one more question! For the hearth base, which will be roughly 77" x 86", and the situation I am with the edges airborne, how many pieces of rebar should I put into the slab? Any suggestions you have will be greatly appreciated.


                  • #10
                    Originally posted by RyanCD
                    Oops one more question! For the hearth base, which will be roughly 77" x 86", and the situation I am with the edges airborne, how many pieces of rebar should I put into the slab? Any suggestions you have will be greatly appreciated.
                    Here's what the instructions propose:
                    Originally posted by FB Pompeii instructions
                    Lay a grid of 1/2" rebar slightly shorter than the external dimension of the wood forms, on 12" centers, starting 6" in from the edges of the form, directly on the concrete. This will set your rebar roughly halfway inside the concrete pad, enabling it to hold up your oven across the opening of the stand (Photo 6).
                    That's what I plan to do, 12 inches apart, six inches in from the end, the grid tied together with wire ties.

                    Just keep the rebar away from the edge. Rust can stain the concrete, and eventually bust up the slab.
                    My geodesic oven project: part 1, part 2


                    • #11
                      sizing slab to avoid cutting blocks for base

                      Sizing your slab to avoid cutting blocks on your base.

                      (These are pretty intuitive to people used to working with block - but for many of us it is our first time.) These rules apply when using mortar joints between blocks and are still a good rule of thumb for non mortared joints. Pls forgive if these are posted previously...

                      1. Using an even number of feet (2 ft., 4 ft., 6 ft., etc.) will always work out in full-and half-block.

                      2. Using an even number of feet plus 8 in. (2 ft. 8 in., 4 ft. 8 in., 6 ft. 8 in., etc.) will always work out in full-and half-block.

                      3. Using an odd number of feet (5 ft., 7 ft., etc.). will not end in full-and half-block. But an odd number of feet plus 4 in. (5 ft. 4 in., 7 ft. 4 in., etc.) will always work out in full-and half-block.
                      Last edited by christo; 07-30-2006, 06:42 AM. Reason: add mortar comment
                      My oven progress -


                      • #12
                        Cutting blocks for the stand

                        What is the general view from past builders? Is it worth trying to avoid making cuts in the block stand, or is it better getting the stand size you want?

                        My experience is that it really is not difficult cutting concrete blocks. You can do it with a basic skill saw and a $15 diamond blade from Home Depot. Noise and dust, but that's it. In a pinch, you can even score the block, and hit it with a hammer, and hide the rough edge with mortar.

                        What do y'all think?
                        Pizza Ovens
                        Outdoor Fireplaces


                        • #13
                          Block Cutting


                          From my experience with block work, I'd say go for the size you want. Cutting with a saw or even with a bolster and hammer is not that difficult, and any rough edges will be hidden by mortar and facing treatment. The only important thing is to make sure that any cut block retains its webbing. Personally, I prefer to cut the wall blocks and always use corner blocks, because this helps with squaring up the stand. On a related issue, I always use a block pointer to dress the joints before they dry. This is less for appearance than for sealing and strength.

                          "Made are tools, and born are hands"--William Blake, 1757-1827