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Filling joints in hearth slab? - Forno Bravo Forum: The Wood-Fired Oven Community

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Filling joints in hearth slab?

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  • Filling joints in hearth slab?

    Hi, my oven that I'm about to assemble has a 4 section hearth slab and a 4 section dome. I've fibre blanket to cover it and it'll then be covered in vermicrete. The kit came with a bucket of masonry cement to stick it all together. Should I fill all the joints in the hearth and dome completely with this refractory cement also or should it be used sparingly?

    Thanks

    Richard

  • #2
    Re: Filling joints in hearth slab?

    The floor should not be mortared in any way.

    Not itself to itself or floor to dome.

    Floor should be allowed to float free. And separate from dome.
    Chip

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    • #3
      Re: Filling joints in hearth slab?

      Thanks Mr C, so ill just use mortar to stick it to the vermicrete slab underneath?
      I assume that's ok?
      Also, why isn't it mortared to the dome, seen as the dome sits directly onto the base?
      Thanks

      R

      Comment


      • #4
        Re: Filling joints in hearth slab?

        It sounds like your oven did not come with any instructions.
        The floor of the oven tends to heat faster and therefore expand more than the base of the dome, setting up thermal stress.The floor bricks are usually set on a dry mix of sand and clay so they will be level but are left free to expand.
        Kindled with zeal and fired with passion.

        Comment


        • #5
          Re: Filling joints in hearth slab?

          Yes, there are some instructions but they're kinda sparse and don't give much info

          Comment


          • #6
            Re: Filling joints in hearth slab?

            Rich,

            I also purchased a composite oven & I agree the directions are pretty basic. If you look at the DaveMartin build it'll give you some nice pics to look at. It is my understanding to just use the mortar on the pieces after they are together in the joint and on either side. Dave (West Virginia), shows a nice picture of this. Then you use mortar around the base of the pieces where it meets the base and he shows a picture of this as well.

            Comment


            • #7
              Re: Filling joints in hearth slab?

              Thanks KKG, ill check that out

              Comment


              • #8
                Re: Filling joints in hearth slab?

                Originally posted by RichC View Post
                Thanks Mr C, so ill just use mortar to stick it to the vermicrete slab underneath?
                I assume that's ok?
                NO! "The floor should not be mortared in any way!!!! It needs to float free.

                Also, why isn't it mortared to the dome, seen as the dome sits directly onto the base?
                The floor and dome expand and contract at different rates and bonding them together will promote cracks.
                Chip

                Comment


                • #9
                  Re: Filling joints in hearth slab?

                  Thanks MrC! Lucky I asked.

                  Comment


                  • #10
                    Re: Filling joints in hearth slab?

                    The composite oven pieces are grooved to fit on top of the floor & extend to the base. It is at the base where mortar needs to be applied as well as the small joint of the oven pieces. If you look at Dave Martin's build you will understand what I am describing.

                    Comment


                    • #11
                      Re: Filling joints in hearth slab?

                      Originally posted by kkgator View Post
                      The composite oven pieces are grooved to fit on top of the floor & extend to the base. It is at the base where mortar needs to be applied as well as the small joint of the oven pieces. If you look at Dave Martin's build you will understand what I am describing.
                      Follow the instructions of the manufacturer, but your photos on your mobile oven clearly show that the dome does not sit on top of the floor, it sits on the insulation and the floor sits inside the dome. The gap between the floor and dome sections is better left empty and allowed to fill with ash IMO so the floor will have room to expand. Likewise the gaps between each of the floor bricks. If this is contrary to the manufacturers instructions I apologise, you should do what they say. As you have already filled them it may be too difficult to change anyway.
                      Last edited by david s; 08-27-2013, 03:22 AM.
                      Kindled with zeal and fired with passion.

                      Comment


                      • #12
                        Re: Filling joints in hearth slab?

                        Hi there- for my casa 90 kit, the oven floor pieces rest on a bed of sand directly on the fiber board floor insulation, then the dome pieces surround the floor and also sit on the fiber board. I raked ashes in to the cracks from my first few curing fires and seems to work well so far!

                        Comment


                        • #13
                          Re: Filling joints in hearth slab?

                          How big cracks are you talking about?
                          My bricks fit pretty tight, but they are a little uneven.
                          A few weeks ago, I used a small angle grinder with diamond cutting wheel to level the bricks--worked like a champ.

                          When I clean my oven for doing bread right on the hearth brick, I use a section of copper tubing and my airhose and compressor. I use my blow gun to direct air into the copper tubing--this loosens all the crap that is floating inside the oven. Keep it blowing and the crap stuff goes out the chimney. I have done this several times in prep of baking bread. In the case of pizza, I only use a bamboo street broom to move things out of the way.....the broom starts on fire--but that is OK. The majority of the ash is out of the way! What remains is seasoning for the first pizzas!

                          OPEN FORUM QUESTION! What do you throw onto the hearth to see if it is hot enough?

                          Comment


                          • #14
                            Re: Filling joints in hearth slab?

                            Originally posted by mikku View Post

                            OPEN FORUM QUESTION! What do you throw onto the hearth to see if it is hot enough?
                            The beam of light from my IR thermometer.
                            Chip

                            Comment


                            • #15
                              Re: Filling joints in hearth slab?

                              I am often up too early to sometimes accurately describe what my thoughts are on any given subject. I agree that nothing inside of the oven should be mortared. My pics just show sand that was used underneath the floor tiles & the floor insulation. The only joint that should have mortar according to FB is on the outside of the composite pieces where they meet. The outside base where it meets the insulation should also be mortared. I have not mortared any joints or floor tiles as I agree with MRC that it should be loose to allow for expansion & contraction during heating & cooling.

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