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30" castable dome

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  • 30" castable dome

    Hi All,
    I would like to start by sincerely thanking all of you that are making this information sharing forum available . been browsing for few weeks as I started building process.

    I have been cooking pizzas for about 10 years now, started in home oven and graduated to a small portable wood woven last few years and am now ready for the next step with building my oven.
    Originally from Naples Italy so grew up eating it, moved to states in 1980 and have been searching for that flavor ever since. Gave up and decided to make it myself that's how it all started.
    Now that Neapolitan pizza is getting more popular there are actually a few places here in the Atlanta area that make some pretty good pizzas, but I must say mine is right up there with the best of them.
    I went back to Naples in May and took a 1 day class at VPN to perfect my craft. Was a blast and learned quite a bit.
    Ok, now on to the build questions....

    I'm just getting started with my build, I have mold ready for a 30" castable dome.
    I have a refractory supplier relatively close by that sells castable refractory cement but reading this forum I'm noticing the "homebrew" popularity so I had a few questions.

    1. Is the preference for homebrew based on price and availability or is it a better mix? If so how?
    2. If going with homebrew , is it all readily available at Lowes/Home depot ? Can someone share exact ones, looking at lime and seeing many different ones on market.
    2. Saw some 30" domes on forum being built with different thickness walls , I have mine measured out at 60mm. Wondering if tat will work fine.
    3. Planning on casting Flue gallery , are there plans available for form build anywhere ?

    I'm sure I will have many more questions as I get into it but would like to start with above and ask you guys for direction.

    Pics show the mold so far, the white band around the circumference of the dome is a flashing strip I purchased from Lowes to help to maintain a consistent wall thickness of 60 mm and figured it would also help with giving bottom row some extra rigidity as I build up the sides.
    Please disregard the flue gallery as after reading some posts on this forum I have decided to cast it separately as mentioned above in one of the questions. And also the duct tape roll on top of dome is just resting there, not part of the mold

    Thank you all in advance for whatever help you can provide.
    Gianluca ( john )

  • #2
    B861D050-1CD8-4832-B034-9ED82AF515BF.jpeg Click image for larger version

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ID:	417424 So , as you can see from The pictures now, I have changed design a bit.
    i found a refractory cement 112lb cft , I need 2.4cft total, so oven will be 270lbs total.
    since I’m casting in basement and not where oven will ultimately be, I decided to cast it in 4 pcs so will be lighter to transport .
    will then join all seems with refractory mortar.
    stay tuned, hopefully all will go well.
    Last edited by gianlucaf; 10-19-2019, 09:16 AM.


    • #3
      Hi Gianluca,

      First up it looks like you are building a hemisphere. Generally Neapolitan pizza ovens have a dome that has its internal dome height less than half the dome’s diameter. This produces an oven with the crown of the dome closer to the pizza which cooks the top of the pizza a little faster.
      1. The preference for homebrew is based purely on price. Castable refractory is expensive as no doubt you have found. It also has a disadvantage in that it sets very quickly. Make sure to mix smaller batches and wash equipment scrupulously before mixing more, otherwise any residue from the previous batch will accelerate the next one.
      As the oven will only see temperatures of around 550C Max a castable refractory rated to around 1400C is a waste of money. It contains high temperature aggregates not required for our temperature range. Ordinary sand will suffice in its place. The high temperature calcium aluminte cement works well in our temperature range but is expensive and has disadvantages as previously described. In its place a mix of 50/50 Portland cement and lime in combination work together adequately (just) in our temperature range. Portland cement begins to degrade above 300C and lime above 500C. The theory is that where the Portland begins to degrade the lime takes over. It has proved adequate for many builds.

      2. The homebrew is 3:1:1:1 by volume of sand, Portland cement, hydrated lime (that’s builders lime not agricultural lime), powdered clay (cheapest source should be bricklayers clay, or often called fire clay) In addition you must add some burnout fibres which assist in safer water removal, largely preventing steam spalling. These are already added to a proprietary castable refractory but if making your own homebrew you need to add them. Approximately half a handful for every 10 litres of mix. The take a while to disperse so mix way longer than you would normally. Use the very fine polypropylene fibres used for concrete reinforcing.
      Cast ovens are generally 50 mm thick but 60 would be ok too.
      3. There are a number of well documented cast builds on this site if you search.

      Kindled with zeal and fired with passion.


      • #4
        Thanks David,
        thanks for your tip, just finished casting, took 5 x 55lb refractory cement and about 5 hours... refractory definitely set up fast, I actually found it at a pretty decent price.
        So took your advice and mixed up little at a time. That was really the hardest and most tiring part
        rest went pretty smooth.
        now my plan is to let it set for few days then remove it from form one piece at a time and let it finish setting another few days.
        depending on weather next weekend I could start the floor .

        ref floor - I have a 3” cement pad on a steel frame built on my deck.
        I have sand , insulating boards and fire bricks , thinking lay the sand on top of cement pad to level all , then 2” insulating board , then firebricks for cooking floor.

        1. Should I seal the cement pad or does it matter ? I’ve seen videos where
        people put aluminum foil on cement, so just wondering if anything should be done to cement pad.
        2. sand, insulating Board then fire brick ,, is that correct?
        3. Should I use anything to set the firebricks (mortar) in place or just sit them on top of board ?
        Attached Files


        • #5
          With the method you’ve used, if laying up the castable without an outer mould, it makes it impossible to vibrate the mixture once placed. This then usually results in some voids against the inner surface. They should be filled ideally about 48 hrs after casting so the casting still contains sufficient moisture that any subsequent castable will bond well with. CAC achieves full strength in 48 hrs so it is safe to de mould fairly early.

          1. If your oven is out in the weather then sealing the top surface would be a good plan to prevent rising damp. A concrete or stone sealer should be adequate for this. Also a good idea to drill a few weep holes through the slab to assist water elimination, should the insulation board get wet.

          2. The usual order is slab, insulation, levelling mix, fire brick floor. Although if your slab is not level you could use a levelling mix between the slab and insulation too.

          3. Fire bricks are often inconsistent in size and some levelling mix will work to make them level. A dry mix of 50/50 sand, powdered clay works well. A wet mix is very difficult to apply to the highly absorbant insulating board and the floor bricks require movement to cope with uneven thermal expansion, so are better laid loose.
          Kindled with zeal and fired with passion.


          • #6
            thank you so much for taking the time to address my questions in a very detailed manner.

            You mentioned CAC fully cures in 48 Hours , guessing that's short for refractory cement (btw, I used econocast 26tr from allied minerals), so thinking I should de-mold and fill in voids sometime today after 24 hours ? will it be cured enough to hold it shape and not fall apart ?

            Your advice on floor is well noted , hopefully I will get to that step next weekend.
            very excited to finally have this build going.
            been in the works for the last 3 years

            thanks again david


            • #7
              Yes, CAC (calcium aluminate cement)
              Kindled with zeal and fired with passion.


              • #8
                De-molded and filled in few rough spots on the underside .
                next step will be to build the floor .
                so far so good .
                Attached Files


                • #9
                  ok, few questions:
                  1. Should I use the same refractory cement to join these pieces together or should I use a mortar ?
                  I know there will be some fairly large gaps between the pieces so not sure if mortar or same refractory cement would work best.

                  2. should I take the time to smooth out the inside of the dome or will it really matter ? it's a bit rough but not sure how/if it will make a difference. not concerned aesthetically.


                  Last edited by gianlucaf; 10-21-2019, 10:17 AM.


                  • #10
                    Oven’s soon to be home
                    Attached Files


                    • #11
                      1. The coarse aggregate in the castable makes it unsuitable as a mortar. You could sieve it out and replace it with sand as previously described.
                      2. Filling the voids on the inner surface needs to be done while the casting is still moist, usually a couple of days after casting. Sieve out the coarse aggregate from a small amount of castable and mix in a little water to peanut butter consistency, forcing it into any voids. If the casting is too dry moisture will be drawn out of the mix too fast and it will not have time to adequately hydrate, resulting in failure.
                      Last edited by david s; 10-27-2019, 12:10 PM.
                      Kindled with zeal and fired with passion.


                      • #12
                        Thanks David .
                        i have already used the castable to fill in voids.
                        it didn’t dry to same color as you can see in some previous pics . I sanded it down yesterday with 60 grit drinking disc and it came out pretty good , looks like it’s in there pretty good hopefully will hold up fine.

                        thanks for the tip on the mortar David

                        iM prepping the floor now . I have 1-1/2” ceramic board .
                        since I want to bring up the floor about another 6”,
                        Thinking will do few inches of vermiculite and cement , ceramic board , sand fire clay dry mixture and fire bricks .


                        • #13
                          Progress Click image for larger version

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                          • #14
                            My very first arch not perfect but proud of it. Learned a lot .
                            Attached Files


                            • #15
                              Hi all
                              Have some questions on flue gallery and chimney .
                              So, I’m done with arch , took form off after about 24 hours and still standing !!! Victory !! Although
                              1.Its a bit crooked on left side , slight bowout so may consider buttress column. But feels very solid , used refractory to join fire bricks . Thought ? Suggestions ?

                              2. Pics attach show opening for flue gallery . Dome arched entryway measures 16” wide by 9 3/4” height , its a 30” inner diameter dome .
                              Flue gallery opening measures 14 1/2” , wondering if good size ? Should I go smaller ?

                              3. planning on tapering it up to a 5” dia chimney opening, Thinking about casting flue gallery out of an insulating castable refractory “ econolite” , then get a 5” stainless chimney pipe or just use refractory bricks to do rest of chimney .
                              could I use regular clay bricks there instead of fire bricks ?
                              does anyone have plans for the form of flue gallery ? How should the tapering go ? Does it matteR ?

                              sorry for all the questions , first Oven and first masonry experience and kind of stuck at this point , looking for guidance .

                              once I have the flue gallery complete I will insulate with minimum 2” ceramic blanket then about a 1” layer of that castable insulating refractory.

                              then after that I plan to start curing fires .
                              once cured , I plan to paint on a waterproof coat of blue aqua gard from Lowe’s

                              then a final layer of stucco , but may go with tiles

                              thoughts on above layed out steps ?

                              Attached Files
                              Last edited by gianlucaf; 11-10-2019, 03:36 PM.