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Barrel Vault Design in NC - Forno Bravo Forum: The Wood-Fired Oven Community

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  • #16
    Today the dome form was finished and I started laying out bricks to see how the bricks would lay out on the slab, There is still much confusion about how the chimney arch should be built but I will worry about that later. The dimensions of the floor are finalized so the hearth insulation can be cut to size.

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    • #17
      Hope you are right. The Roxul Comfort board 80 has compressive strength at 10% is 439 PSF which equates to abt 3 PSI. I kind of equate this to putting on home slab on a old land fill that has not been compacted versa building on compacted structural fill. But it is your choice. Why not consider using 8 to 1 pcrete under the floor it almost has the same K value as CF board and inexpensive and probably cheaper than the Roxul board.
      Last edited by UtahBeehiver; 09-29-2016, 11:47 AM.
      Russell
      Google Photo Album [https://photos.google.com/share/AF1Q...JneXVXc3hVNHd3/]

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      • #18
        Maybe you could cut some strips of the stronger insulation board to place down first, then in fill with the Rockwool. Or if you don'5 have enough you could create some stilts with 5:1 vermicrete. Unfortunately Rockwool insulation has a higher water absorbency rate than pretty much any other insulation type.
        Kindled with zeal and fired with passion.

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        • #19
          Originally posted by Ron-NC View Post
          Today the dome form was finished and I started laying out bricks to see how the bricks would lay out on the slab, There is still much confusion about how the chimney arch should be built but I will worry about that later. The dimensions of the floor are finalized so the hearth insulation can be cut to size.
          Make sure you put some wedges under the arch form so when you want to remove it the thing will drop a little.you will need to cut some access holes in the front board so you can access the wedges at the rear.
          Last edited by david s; 09-29-2016, 01:18 PM.
          Kindled with zeal and fired with passion.

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          • #20
            Utah, you are totally correct about the compression info. This Roxul board is definitely spongy (I cut both insulations today). So, thinking about the sequence, I am thinking it would be best to layout the insulation and then pour the perlcrete around the insulation to minimize any lateral movement of the Roxul from the bricks. Then, after the perlcrete sets, I would add the bricks which hopefully would compress the Roxul more uniformly. Are you suggesting that an 8:1 mix of perlcrete would still provide the support in this rather unusual application. Time will tell if this less expensive approach works!

            David, I have a bunch of 1 1/4" X 1 1/4" X 5 foot long wood that I am planning on putting under the form, which I was thinking I would be able to easily pull out. Do you think this will work or am I missing something? You are right about the absorbancy of the Roxul, I will have to make sure no moisture creeps into this oven.
            ron

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            • #21
              Originally posted by Ron-NC View Post
              Utah, you are totally correct about the compression info. This Roxul board is definitely spongy (I cut both insulations today). So, thinking about the sequence, I am thinking it would be best to layout the insulation and then pour the perlcrete around the insulation to minimize any lateral movement of the Roxul from the bricks. Then, after the perlcrete sets, I would add the bricks which hopefully would compress the Roxul more uniformly. Are you suggesting that an 8:1 mix of perlcrete would still provide the support in this rather unusual application. Time will tell if this less expensive approach works!

              David, I have a bunch of 1 1/4" X 1 1/4" X 5 foot long wood that I am planning on putting under the form, which I was thinking I would be able to easily pull out. Do you think this will work or am I missing something? You are right about the absorbancy of the Roxul, I will have to make sure no moisture creeps into this oven.
              ron
              you need wedge shaped timbers to allow the form to drop or it will not release without wrecking the arch or vault so you need to be able to reach in and tap them loose do not underestimate how tight they will be

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              • #22
                Thanks guys about the wedge advice; I'll cut some access holes to reach some wedge shaped devices

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                • #23
                  I miss spoke should be 5 to 1 for floor. 8 to 1 is for dome insulation. David brings up a good option of pouring stilts of p-crete to support the floor. We are just wanting you to be successful.
                  Last edited by UtahBeehiver; 09-29-2016, 07:30 PM.
                  Russell
                  Google Photo Album [https://photos.google.com/share/AF1Q...JneXVXc3hVNHd3/]

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                  • #24
                    Thanks . I also found sports grade at ACE apparently as marker etc

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                    • #25
                      thanks Utah for the Perlcrete ratios; hopefully I am not being penny-wise and pound foolish about the floor insulation!

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                      • #26
                        The insulation was placed on the hearth slab today and the 5:1 perlcrete poured around the Roxul insulation. I decided to make the perlcrete 3" thick and will then place 2" of the fiber board on top of the perlcrete (the photos do not show the fiber board yet). The arch bricks and walls will then be placed on the perlcrete / fiberboard area. I mixed the 5:1 perlcrete with 30% water by volume, of all the dry ingredients - something I read from an earlier post from David. This seems to be a very good bench mark with the materials I used - thanks again David, you are truly a wealth of information on this site.

                        I will let the perlcrete setup for a week before I place the two layers of floor bricks. Next I will pick through the bricks and select the best I have for the floor (the 100 yr old red clay bricks have a lot of variation).

                        Once I lay the first floor layer of red clay bricks, I am thinking of using 50/50 fine sand / fire clay for the leveling agent. Does this make sense or would it be better to use home brew to better mortar the first brick layer in place. I can use either but would want to use whatever material would best promote heat transfer from the fire brick to the red clay layer - thanks
                        ron

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                        • #27
                          Ron,

                          the sand/clay levelling mix can be done wet or dry. If left dry it allows some free movement of the floor bricks to expand and contract. Also it enables replacing any floor bricks easier should that need ever occur in the future. It will take more than a week to dry the 3" vermicrete layer. More like 3-4, but it will eventually dry from firing. If good drying weather though, it doesn't hurt to leave it uncovered for longer if possible before building over it. See my experiment attached.

                          Dave

                          Vermicrete insulating slab copy.doc.zip
                          Last edited by david s; 09-30-2016, 11:07 PM.
                          Kindled with zeal and fired with passion.

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                          • #28
                            thanks Dave, I will let the perlcrete dry out longer which is probably a good thing since the temperature is still hot around here. Also, since I am near the beach, the humidity is always high. I was also leaning toward using sand/fireclay as the leveling agent and will send out a pic of the first layer of red clay bricks prior to covering them with the leveling agent.
                            ron

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                            • #29
                              I took a bit of a break due to hurricane Matthew coming through our area. I covered up the perlcrete layer with a couple layers of plastic / bricks and it stayed dry despite 100 mph winds and heavy rains. So this past week I was back at it. This first pic shows the first layer of red clay bricks sittiing on top of the insulation. A few of the fire bricks are on top of the first layer for perspective. There are still 2" of floor insulation exposed which will be surrounded by fiber board / perlcrete.

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                              • #30
                                Next, I raised the perlcrete form by 2" in order to place 2" of fiber board insulation around the existing floor insulation, on top of the existing 3" of perlcrete. The perimeter / wall bricks will sit on top of the fiberboard which should provide a stable floor for the arch walls. After the fiber board was set in place, it was surrounded by perlcrete to "lock in" the insulation.

                                While the perlcrete dries, the firebricks were cut in a herringbone pattern for eventual placement over the first layer of bricks.

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