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new adobe oven plan - pls comment

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  • new adobe oven plan - pls comment

    Hi all,

    I plan to build small adobe oven to try the whole WFO thing :-)
    It's mostly for pizza, may be some bread, occasional use.

    Please comment/critique my current plan.

    1. dry stack 4 pillars out of cement blocks on the ground, no foundation. If the
    oven moves and cracks a bit - no big deal, it's temporary.

    2. Construct form out of 2x4 (go 2x6?) wood with plywood bottom. Pour 1:6 cement
    to vermiculite into it. I suspect I might need some re-bar and a thin layer
    (1"?) of regular concrete at the bottom to strengthen it up? I don't know what's
    the strength of vermiculite/cement mix..?
    Should I go with thicker base?

    3. Dry lay 2.5" fire bricks flat for the hearth.

    4. Mound sand for the shape, cover with paper

    5. Mix Hawthorne 50 clay 1:3 with sand (I can get either masonry or concrete

    6. Shape the round dome

    24" internal diameter
    14" int height
    12" wide door
    9" door height
    4" thick walls

    Should I consider chimney?

    7. cut the door, dry the walls (wait few days?), take out the sand, make fire,
    bake pizza :-)

    8. Optional - insulate by 3-4" of 6:1 vermiculite/cement mix?


  • #2
    Re: new adobe oven plan - pls comment

    ok, makes sense. I mentioned in step 2, I probably need reinforced concrete as a base...

    How hard would it be to stick a chunk of 4" duct pipe in as a chimney...
    Is it worth it..?


    • #3
      Re: new adobe oven plan - pls comment


      sounds all good. Do you happen to have a copy of Kiko Denzer's book?
      that is the perfect manual for an earth oven.

      I just finished the dome of my earth oven this weekend, and your plans look very similar to what I did.

      (ignore the rocket stove that is underneath the oven, that is just one of the quirky things i wanted to try out. It could be usefull to pre-heat the dome and chimney i guess but I don't think it will be able to heat up all the mass. The oven is just to big.)

      I would recommend a chimney. If it was only to not burn you face and have black soot all over the front of the oven.

      good luck


      good luck
      Last edited by thijsatteiltje; 05-05-2012, 02:06 AM.


      • #4
        Re: new adobe oven plan - pls comment

        Thanks. I read the book, but don't have it handy now.
        Where should I place the chimney and what materials to use for it?

        very nice over in the pics, how big is it?
        What did you use to plaster the top white?
        Nice view - where is it? Oh I see NZ :-)

        Thanks again


        • #5
          Re: new adobe oven plan - pls comment

          Well, technically, my chimney is not in the right spot. That is because I was also debating until the last moment if I should put one in.

          See my discussion about it here: http://www.fornobravo.com/forum/f9/h...int-17638.html

          Ideally, the chimney should be inside the door arch, at 63% of the inner dome height.
          In my case, with a brick arch, that meant a more complex construction of the arch to accommodate the flue opening, which I did not feel comfortable with at the time.
          Looking back now it would not have been so hard.

          If you make the door arch from cob (straw and clay) you have a lot more freedom of course. To get an actually updraft the chimney needs to be a certain height (at least 3 feet i believe, but check the forum) and it should heat up quickly. So either stainless steel (don't use galvanized pipe, it will give off nasty fumes) or some sort of insulated cob/clay/straw/sawdust mix. but making a 3 foot clay chimney might be tricky ;-)

          But... as you can see from the last comment on that other discussion, although placing the chimney in the door arch is ideal, placing it just behind the arch will probably work as well.

          These are the measurements:

          inner diameter: 80cm/31.5"
          inner height: 43cm/17"
          stem wall: 10cm/4"
          door height: 27cm/10.5"
          door width: 47cm/18.5"
          wall: 8cm/3"

          I found this handy calculator:
          Dome Calculator | Monolithic

          tip: Make at least 1.5 times more clay mix than you calculate. You will need it as lot's is lost in spillage and somehow you always tent to make the walls thicker than you thought.

          tip2: cut the shape of the dome out of a thick piece of plywood, you can use it to measure your progress and even very easily 'press' the clay back into shape.

          I found that just having the thing have beautiful shape adds so much to the enjoyment of the end result. Also, correct dome shape will be stronger, i understand.

          Use a lime and sand plaster for the top. don't use a cement based plaster as the clay will always attract moisture from the air and needs to evaporate this again.

          You can get nice cement colours (cheap) to give it a nice colour.
          (if you want bright colours, use white plaster sand instead of normal gray sand for the lime mix, otherwise the coulor might come out a bit muddy) (no pun intended)


          (p.s. I'm sure they have pretty decent views in Canada? ;-)


          • #6
            Re: new adobe oven plan - pls comment

            Originally posted by h&t View Post
            ok, makes sense. I mentioned in step 2, I probably need reinforced concrete as a base...

            How hard would it be to stick a chunk of 4" duct pipe in as a chimney...
            Is it worth it..?
            For me it is, but realise that with a 4" pipe you will still have some smoke coming out of the doorway.

            But, even if this is a temporary/first pancake trial, think of how much you would learn from putting in the chimney. That would be invaluable for a next/bigger/better project.

            I just place mine on top of the brick arch and attached it with screws to the brick. If you are only going to have a cob arch you could do some cut-ins around the bottom and fold those horizontal so the clay has something to cling to.

            (duct pipe is prob zinc or galvanised (or is that the same?), not recommended for high heat)



            • #7
              Re: new adobe oven plan - pls comment

              Matt, thank again for all the help. Or should I say bedankt? :-)

              I think I need brick arch and a chimney. Why do these projects always get more complicated than one envisions..?


              • #8
                Re: new adobe oven plan - pls comment

                thanks, that's useful


                • #9
                  Re: new adobe oven plan - pls comment

                  the oven is finished, first pizza cooked today


                  • #10
                    Re: new adobe oven plan - pls comment


                    • #11
                      Re: new adobe oven plan - pls comment

                      he, that looks great!

                      How easy was it to keep a good fire going and get the dome to temperatur?

                      I found that having a steel firedoor really helps the chimney drawing and keeps the black stuff off your door opening.

                      Here are two pictures of mine. (it needs some insulatation on the fire side because the wooden handle starts to burn)

                      The surface area of the slot is identical to the surface area of the chimney.

                      Attached Files


                      • #12
                        Re: new adobe oven plan - pls comment

                        I am still waiting for the IR thermometer I ordered...
                        I had the fire for an hour or more... When I put the first pizza in the oven semolina from the peel burst into flames :-) so I think may be the floor was too hot.
                        I didn't time how long the pizza was in the oven, but I could see the crust spring like someone was inflating it :-)

                        Your arch looks so much better than mine :-)

                        What did you use for the fire door material? is it just plate of steel? how did you cut it?


                        • #13
                          Re: new adobe oven plan - pls comment

                          It is really funny that our projects are so in sync: I am also still waiting for my IR thermometer ;-) I did a test with rack of lamb and veggies after a long drying-session, it was delicious. If the weather holds I might try the first pizza tomorrow night.

                          I use an oven tray (from the landfill shop) for the fire door. I cut in the corners and then hammered the sides flat. I used a normal angle grinder.

                          The oven pan is made out of non-galvanized steel. It is painted but I reckoned even if the paint burns off , the fumes would not be to deadly as it is supposed to be a food container, right? ;-) (yes, I realise that is not logical, a domestic oven does not go above 250c but I don't think that after a couple of burns any nasty things will get in the food)

                          To insulate it, i think i will somehow mount another sheet in front of it, maybe by folding the edges over and fill the gap between the sheets with pumice or clay/sawdust mixture.

                          Maybe for the fire door the pumice is not needed and just two sheets of metal are enough to prevent the door handle from charing. You could also put the handle on pieces of thread or long bolts so the wood does not touch the metal.

                          I was considering these thick, sturdy aluminium BBQ plates you can get at the supermarket, but aluminium might continue to give off fumes when super heated, so perhaps not such a good idea.



                          • #14
                            Re: new adobe oven plan - pls comment

                            would you share the lamb recipe? I have a bunch of people over tomorrow, would be nice.


                            • #15
                              Re: new adobe oven plan - pls comment

                              Originally posted by h&t View Post
                              would you share the lamb recipe? I have a bunch of people over tomorrow, would be nice.
                              Recipe, he? ;-)
                              I think i even followed some remarks from this forum:

                              rub the rack with a mixture of lemon juice, olive oil, salt, pepper and rosemary and just stick it in an oven tray. No need to pan fry the outside first to get that caramelisation, the heat in the oven will do that fine.

                              Like the other post said, cover it after 15 min and then let if sit in the oven for another 10-15 (depending how red you like it)

                              good luck!