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Cracks in pad that oven is sitting upon - Forno Bravo Forum: The Wood-Fired Oven Community

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Cracks in pad that oven is sitting upon

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  • Cracks in pad that oven is sitting upon

    We have just installed a modular oven building it from the ground up. It is built with concrete blocks with a reinforced concrete pad (w/ sand) built on top of the blocks. We inset the oven in the pad so that the floor of the oven is level with the pad.

    The problem is that thermo dynamic cracks have appeared directly in the center of three sides of the pad and when it rains, water intrudes and dampens the inside of the oven. Two of the three cracks are very small, but one exceeds 1/16" when the oven is at it's hottest. The cracks retract when the oven cools.

    We are going to tile over the cracks using flexible mortar and grout but I fear the one big crack will crack the tiles when it expands under heat because the mortar we are using says it will expand no more than 1/16".

    Does anyone have any other suggestions for materials or fixes to use in this situation?

    Thanks for any input.

  • #2
    Re: Cracks in pad that oven is sitting upon

    maybe a photo will help.

    the crack expands and contracts with heat and cooling, but water will intrude into the dome which wets the oven floor.

    We would like to tile over the entire pad hoping that the tile will cover the crack, stop the water intrusion and look nice. But we are afraid the tile will crack as well.

    Ideas we have:

    1. Tile with flexible mortar and grout and hope that the mortar and grout take the expansion so the tiles won't crack.

    2. affix, some way, a piece of metal over the crack and then set tile over the metal (proper adhesive?) so the crack can expand and contract under the metal w/o affecting the tiles above.

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    • #3
      Re: Cracks in pad that oven is sitting upon

      Grind it out a minimum of 1/4x1/4 and fill with a good quality polyurethane caulk. 3/8x3/8 would be better, but in either case make sure the joint is very clean before applying the caulk.

      Edit- If you are going to cover with tile, you need a slip shield at least 10x the width of the crack. 20 mil poly flashing cut to size will work fine.
      Last edited by Tscarborough; 12-04-2010, 10:23 AM.

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      • #4
        Re: Cracks in pad that oven is sitting upon

        Take it apart.

        Redo the slab and sit the insulation and oven on top (not inset).

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        • #5
          Re: Cracks in pad that oven is sitting upon

          Can you share with us exactly what insulation you put under and around the oven?

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          • #6
            Re: Cracks in pad that oven is sitting upon

            Thanks all for your help.

            First I wanted to be clear, the crack was not in the oven, but simply in the pad we constructed.

            The crack in the pad was tiled over utilizing a product called Ditra that allows for dynamic movement below the tiles without affecting the tiles themselves.

            We do a lot of entertaining and we cook a lot of casseroles, braised and roasted dishes and the smooth transition out of the oven is very helpful when cooking for larger crowds.

            Ron

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            • #7
              Re: Cracks in pad that oven is sitting upon

              "First I wanted to be clear,"

              Could you do a sketch showing the cross section ? By "pad" I take it to mean the suspended structural slab.

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              • #8
                Re: Cracks in pad that oven is sitting upon

                Yes, "Pad" isn't a term we use around here. Most of our ovens are built on a support slab of reinforced concrete, with an insulating layer above it. Sometimes the edges of this layer are raised up above the insulation so that, as you say, the floor of the oven is flush with the landing.

                I've never heard of ditra.

                Your picture, although very explicit in showing the crack, doesn't make it clear where it is. As Neil says, a sketch, or a larger picture to put the crack in context, might help us know what your problem is.

                My worry is that, if your support slab is heating up enough to expand a crack when the oven is fired, you may have a serious problem with your under-oven insulation.
                My geodesic oven project: part 1, part 2

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                • #9
                  Re: Cracks in pad that oven is sitting upon

                  Does this "raised" part of the slab continue around the oven, and if so why ? Why would it not be only in front of the door opening ?

                  What may be happening is that, under thermal expansion and contraction, your oven may in some way be "pushing" out against this raised part. Or it may be as dmun suggests, heat transfer to the structural slab.

                  In any case, I would try to get to the bottom of this. Cracking in your suspended structural slab (apart from minor hairline cracks after the initial concrete set) may be serious.

                  For others considering making the landing flush with the floor of the oven, I suggest that this landing be a separate pour and not be an integral part of the structural slab.
                  Last edited by Neil2; 01-21-2011, 03:28 PM.

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