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35 inch Pompeii Oven Build Saga - Forno Bravo Forum: The Wood-Fired Oven Community



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35 inch Pompeii Oven Build Saga

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  • 35 inch Pompeii Oven Build Saga

    This is a build log or is it blog of my pompeii oven. I am using the standard plans as my basis with some changes I have seen on the forum and a few twists of my own.

    The internal diameter is 900mm which is 35.4 inches, so nearly a 36 inch oven !

    The base is made of blocks with a ground smooth finish plus two brick arches. So there is plenty of room for wood underneath. The blocks were a small lot from a factory outlet and really well priced.
    Boxing for floor is made of blocks cut down the centre so the floor is contained withing the blocks. This worked well but cutting was really dusty and you could not do it without a diamond wheel.

    I have set up the floor within the block work so the oven floor will ultimately be level with the coping bricks that will finish on top of the blocks.

    On top of the concrete floor I have about almost a 2 inch layer of vermiculite/cement 5:1

    I know this is thin but I am using 2 inch Calcium Silicate board which by the plans is sufficient insulation by itself. The only reason I used vermiculite under the Calsil board is to get my floor level where I wanted it.

    I have read about making the vermiculite/cement and tried both methods dry mix with cement then add water and mix cement and water then mix with vermiculite. I prefer the dry mix with cement first but either way I found it is difficult to work with.

    Pictures are attached .... more to follow soon.


  • #2
    Re: 35 inch Pompeii Oven Build Saga

    I had laid my calcium silicate board directly on the vermiculite/cement but I was not happy with how level it was and I had also decided to put a thermocouple under the floor insulation.

    So I lifted the calcium silicate board out and leveled the surface with a 1:1 mix of sand and fireclay. I know it is not insulating but that is all I had and it is really pretty thin layer. In the first picture attached, I have leveled and floor and you can see where I have put in the thermocouple.

    Now to lay the firebrick floor...

    The firebricks I used were 9"x9"x3" (actually in mm 230x230x75) laid in an offset pattern. On top of the calcium silicate board I used a thin layer of dry 1:1 sand and fireclay to level the firebrick floor. I decided to use a dry mix because the calcium silicate board just sucks up the water and I could not see how a wet mix would work. I had read a number for threads where dry mix was used. It worked fine and I was happy with how they went down and the result - very much like laying pavers (but with a very thin bed).

    For those that are wondering what all the drawing on the floor blocks is... it is where I was drawing and doing trial set outs of the oven floor and then they got all out of order when I laid then properly.

    The black around the laid floor is a small grout of refractory cement around the bottom outer edge just to seal in the leveling layer of the floor. You can also see I have added some extra Calsil board to insulate the ends and the sides. I pushed the base size quite tight and the floor is inside the concrete surround, so I wanted to have a 2 inch Calsil inch layer or 6 inches of vermiculite/cement between the floor and the outer concrete.

    I have used a calcium aluminate home brew mix of crushed firebrick (instead of sand) and fireclay and calcium aluminate cement (CAC). I am still playing with the mix and will do the post just on that subject.



    • #3
      Re: 35 inch Pompeii Oven Build Saga

      Ok getting ready for first course...

      I cut out a template to lay on the floor so I have a guide for the first course plus to keep the floor clean and provide allow mounting for the indispensible tool I made. I am going to use both the tool and a wooden template of the oven wall profile.

      Last picture in this post shows the hole I have drilled in the firebrick floor to insert a thermocouple. I purchased some K type thermocouples from a company in the US which are 6 inches long, made of Inconel 600 alloy and used for glass kiln or heat treatment oven. The maximum working temperature is 1100C (2000F) and the cable insulation is fiberglass with stainless steel overbraid (rated at 900F). They were US$19 each but I had to buy and fit a k type mini plug as they only come with a cripped end suitable for a screw fitting. I will do a photo in a later post.



      • #4
        Re: 35 inch Pompeii Oven Build Saga

        First course of oven

        I have not used a soldier course as I am setting my first course on the oven floor and because I tied a few profiles of the dome and the one that worked the best did not have a soldier course.

        The firebrick i am using are thicker than the plans at 3 inches thick.
        Dome will have an internal height of 18.3" (465mm) with door opening 17.6" (450mm) and door height of 11.4" (290mm) ... that's the plan anyway.

        I have read a few posts that have just sat the first course of bricks directly on the floor but to take up some slight level and size differences I decide to set the first course with a thin layer of 1:1 fireclay and firebrick dust (from cutting the bricks) made to a smooth paste. It was only about 1 mm thick in most cases.

        I trying to build the oven walls with no mortar inside the oven and am pretty happy with how the first course worked out but I suspect it will get harder as I go.

        Next job is to mortar up the triangle gaps in the first course...



        • #5
          Re: 35 inch Pompeii Oven Build Saga

          I said I would do a post on the home brew calcium aluminate mortar I am using. This post is largely a repeat of a post I made about calcium aluminate mortar at:

          I am using calcium aluminate home brew mortar and have started with 3:1:1 crushed firebrick:fireclay:ciment fondu which needed 1 part water. The amount of water is much more than the 40% water to ciment fondu specified in the datasheet but it seems to be due to the firebrick absorbing water. The mix is more like a grout than a mortar and sets hard in about 2 hours (just under 20 Celsius).

          I have done some trial mixes and as I substituted the sand for firebrick less water was required and the mix was more workable. I still needed more than 40% water to ciment fondu specified in the datasheet to get a workable mortar. To one of the trial mixes I added 1/4 part hydrated lime, more water was needed than the comparable mix without lime. The mix with lime though seemed more smooth and workable as a mortar but was solid in 20 minutes at under 20 Celsius.

          I have started filling up the triangular gaps between the bricks in the first course of the oven but for later courses I will really need to use sand instead of the crushed firebrick because the mortar with firebrick instead of sand is not very workable at all.



          • #6
            Re: 35 inch Pompeii Oven Build Saga

            Progressing slowly...

            Onto the second course - I tapered the sides of each brick so there was no mortar gap (or minimal). I am starting to get quicker at setting down the bricks.

            I am now using a calcium aluminate (ciment fondu) home brew mix that is a slight variation to the FB recipe (without the lime !)
            2 parts fine sand, 1 part fine crushed firebrick, 1 part fireclay, 1 part ciment fondu and I use about 1 part water. This is more water than the ciment fondu technical data sheet recommends but I think that is because the fireclay and firebrick absorb water and the data sheet limits water for constrcution maximum strength. I am finding this mix is quite easy to work with.

            I am starting to look at the arch transition and want to do as others have done and cut the arch bricks so there is a downward and upward cut on the inside of the oven to make a smooth transition. Quite a bit of thinking needed and may be a additional marking pen adaptor for the indispensible tool.

            Door opening did work out to 17.6" (450mm) with a 1" reveal

            More progress next weekend I hope.



            • #7
              Re: 35 inch Pompeii Oven Build Saga

              Looking good Brett...a nice clean build


              • #8
                Re: 35 inch Pompeii Oven Build Saga

                I am progressing slowly with just part of Saturdays to work on the oven.

                I have added a course of bricks on the the side of the main arch bricks to provide some extra buttressing. It is only a few extra bricks and will be covered by decorative bricks later anyway.

                I have finally worked out the inner arch brick angles and cut most of the bricks but have to finish cutting the entry return. Only cutting of some outer bricks to go.



                • #9
                  Re: 35 inch Pompeii Oven Build Saga

                  It's looking good. I'm trying to picture the interior arch as you cover it.
                  I'll have to wait for more pictures.
                  My 42-inch build


                  • #10
                    Re: 35 inch Pompeii Oven Build Saga

                    Progressing slowly with only half day couple times a month. Plenty of cutting - the drop saw with diamond blade and hand grinder are getting a workout.

                    Pretty happy with inner arch. Had to move pretty quickly in laying as aluminate mortar goes off within a few hours. But was good as I could remove arch support and clean mortar from lower side of arch within several hours.

                    Row 3 finished now. Takes longer to cut angles on side of bricks and fit than laying the row of bricks !

                    Attached Files
                    Last edited by Mistertoy; 09-28-2011, 07:05 AM.


                    • #11
                      Re: 35 inch Pompeii Oven Build Saga

                      Takes longer to cut angles on side of bricks and fit than laying the row of bricks

                      I hear ya! Any level of craftsmanship takes time but when you're fininshed you can sit back and enjoy the results of your efforts. Fortunately, you do get better and faster at it the further you go. For each phase of my build, by the time I felt I was getting pretty proficient, it was time to go onto the next phase...

                      I say take your time, stay patient, and don't waver from the level of quality you've come to expect of yourself. Your build is looking gutandtite, and I love your arch transition


                      • #12
                        Re: 35 inch Pompeii Oven Build Saga

                        I cannot believe it has been 3 months since I last posted.

                        Well I won't hit my target of finishing by Christmas. May Easter

                        I have really noticed the difference in how fast the calcium silicate mortar goes off now it is summer in Queensland Australia. I have to work in the cool of the day - early in the morning or late in the afternoon.

                        The corner pieces of the arch were tricky and I used mouldable plastic which softens at 60-70 celcius to help get the shape right - happy with the outcome.

                        Will just keep plodding along in summer and might have more time once it starts cooling off closer to winter.

                        Have attached a few photos that I took before I started laying the 5th course today.



                        • #13
                          Re: 35 inch Pompeii Oven Build Saga

                          Looking good...very clean. Some nice cuts too


                          • #14
                            Re: 35 inch Pompeii Oven Build Saga

                            Mate just take your time......you works real neat

                            Regards Dave
                            Measure twice
                            Cut once
                            Fit in position with largest hammer

                            My Build
                            My Door


                            • #15
                              Re: 35 inch Pompeii Oven Build Saga

                              Nice job with the outer arch.

                              I dont think there is much advantage scuffing the bed face with a grinder, if the bricks were to come loose they still will even with the scuffing.
                              The English language was invented by people who couldnt spell.

                              My Build.