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Adhoc 36" Oven in Lake District, UK

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  • #61
    But then, Tues morning this week - woke to Disaster? ?

    My concrete hearth slab revealed a full length CRACK! Side to side, centre of slab, down full thickness.

    Some info - It IS all reinforced with wire mesh (see pics) there are no cracks in brickwork either on slate base walls or inside oven. Exterior of oven - no cracks. Underneath the hearth slab, whilst it gets pretty warm - crack does not show on underside. On top of concrete slab, I used some cement/mortar to place and level ONE calsil board (not two...wish I'd done so!) Then fireclay on top, with oven floor bricks on them.
    Concrete is 4 inches thick at max but as low as 3.25 inch thick (where the crack is on one side)

    The crack is hairline and appears to have closed up a bit more now. The concrete slab sat for weeks before any fires were lit. Boards and supports were under for a LONG while too.All but one of the support legs came out with little or no effort.

    Should I be concerned?

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    • #62
      Could anyone advise on my last post please? Should I be concerned at all? Cheers

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      • #63
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        Micky,

        I would not be to concerned about the cracks it is only hairline you have put enough mesh in the concrete to hold it all together most concrete will crack at some stage thats why they put expansion joints in concrete slabs as I said the mesh is there to hold it all together
        Micky unfortunately people get the use of mesh and reinforcement wrong, mesh is for use when laying concrete on the ground and rebar is used when pouring a suspended slab most would use 1/2 inch rebar for a suspended slab and perhaps F7 mesh for concrete driveways etc

        Cheers Doug
        Last edited by Karangi Dude; 04-18-2019, 02:42 AM.
        https://community.fornobravo.com/for...-s-48inch-oven

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        • #64
          Originally posted by Karangi Dude View Post
          Click image for larger version Name:	image_22364.jpg Views:	2 Size:	132.1 KB ID:	412387Click image for larger version Name:	image_22604.jpg Views:	2 Size:	118.8 KB ID:	412388

          Micky,

          I would not be to concerned about the cracks it is only hairline you have put enough mesh in the concrete to hold it all together most concrete will crack at some stage thats why they put expansion joints in concrete slabs as I said the mesh is there to hold it all together
          Micky unfortunately people get the use of mesh and reinforcement wrong, mesh is for use when laying concrete on the ground and rebar is used when pouring a suspended slab most would use 1/2 inch rebar for a suspended slab and perhaps F7 mesh for concrete driveways etc

          Cheers Doug
          Thanks for the response Doug. Nothing else appears affected. Looking at my pre-concrete pour pic, there is actually doubled up metal mesh around the area of crack. Just caused a minor panic. Don't see anyone else on here with similar issues!

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          • #65
            Remember the old adage "There are two types of concrete pours...those that have cracked and those that will crack." As Doug said, the interior reinforcing (rebar/wire mesh) is the primary factor in the lateral/flex strength for any concrete slab...concrete is providing mostly compression strength. As to others with similar problems...there have been many folks that are concerned with minor cracks in their stand's concrete top platforms. Most folks have done some sort of external enhancement such as tile or stone on their stands and hearth, so you just don't see/notice that fairly common minor cracking.

            Relax and have a tasty, adult beverage to celebrate your excellent build!
            Mike Stansbury - The Traveling Loafer
            Roseburg, Oregon

            FB Forum: The Dragonfly Den build thread
            Available only if you're logged in = FB Photo Albums-Select media tab on profile
            Blog: http://thetravelingloafer.blogspot.com/

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            • #66
              Micky,

              Like the others, I don't think you have anything to worry about. However, you might want to reinforce the hearth with a center support. I built mine in an "H" pattern too provide additional support in the center. If your stand is rectangular you could build a block support/center stand in the middle of your slab?

              Cory

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              • #67
                Thanks for the feedback SableSprings and cbailey Problem I was worried about was - Ive never HEARD that old adage about concrete pours! Ive heard many a time about "There are ovens with cracks and those who lie about the cracks" But seen nothing on the concrete slab as such. Im not worrying about it. The pizzas are coming out really good and I got a fantastic trip advisor review the other day.
                Vermiculite is looking very light in colour now and once its almost entirely that way, I think I'll be ready for my cement and slate rendering. What mix do I use of sand/cement and should I add anything in there to add elasticity (for cracking) or weatherproof related stuff?
                And thanks cory - I do have a central pillar of breezeblocks underneath already. I'd thought that far ahead. Your's looks Nukeproof in comparison mind! Your build is coming along great

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                • #68
                  Originally posted by MickyPizza View Post
                  I crawled inside yesterday and brushed up the offending area. On quite close inspection and given the shee size of the external cracks, nothing to be worried about INSIDE. With the blanket lifted up to photo the cracks the other day there WAS steam coming up through out of them though. Maybe moisture from the external mortar joint and bearing in mind I'm hammer and chisel jobbing it - my mortar gaps are bigger than most folks on here...
                  I scraped the extrnal cracks out and smeared in some heat mortar to repair it. On inspection of my photos though, the second pic perhaps shows a crack my eyes never picked up on (top right)
                  Its nice to see my upper higgedly piggedly courses looking good to go though. Rained all yesterday so created a template for a door. Getting a local blacksmith to forge one for me. No rain today. Heat mortar to be plastered over the cracks today. Then will chicken wire the blanket in place for good!!

                  When I hit top temps, even with all them blanket layers on - it WAS quite warm on top so Im adding some, but not all, of blanket 2 on today.

                  Question.... (maybe for UtahBeehiver r SableSprings ) The blanket has been outside, covered by tarps etc. But - its damp. What do I do? Do I keep lighting fire after fire after fire, till it all dries out before adding the vermiculite/concrete layer. OR can I just light a fire, get the worst of the moisture out and continue on adding the insulating concrete without concern? Thanks guys..
                  Hi Micky, thank you for sharing the sad moments of hammering the last stone in. I feel for you. I am actually running into my 4th year and about to build the dome tomorrow. What would you recommend that I should do when I get to the last top stone? Shall I not hammer it?
                  Well done for accomplishing the oven, hope you enjoy it this summer check this ribs in oven https://www.youtube.com/watch?v=rBtIaHeuvks

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                  • #69
                    Originally posted by Alomran View Post

                    Hi Micky, thank you for sharing the sad moments of hammering the last stone in. I feel for you. I am actually running into my 4th year and about to build the dome tomorrow. What would you recommend that I should do when I get to the last top stone? Shall I not hammer it?
                    Well done for accomplishing the oven, hope you enjoy it this summer check this ribs in oven https://www.youtube.com/watch?v=rBtIaHeuvks
                    Late reply here!! Don't know where you are at on your dome at this stage, but I used a little TOO much force. Get the final keystone as good a (tight) fit as you can before whacking it in. My entire build was done by hand, using a hammer and chisel. All bricks and slate were fashioned by feel, hard battering and luck. I never used any power tools or blades to cut anything to any precision. The early Neopolitan ovens weren't built by Stihl saws and diamond cutters I thought!

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