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Hearth Board Support

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  • Hearth Board Support

    I am going to pour my hearth slab next weekend.

    I've read it both ways, but does anyone have an opinion on cutting the Hardibacker to fit just inside my wood form which would cover the cement blocks, or do I cut the Hardibacker so that it fits inside of the cement blocks and sits only on my wood frame (then remove it after pour)?


  • #2
    Re: Hearth Board Support

    I think the best plan is to have the cement board overlap the block stand a little, but not go to the edge, so your slab concrete can bond to the block stand.

    Putting the form inside the stand is for when you are using a wood form that will have to be removed.
    My geodesic oven project: part 1, part 2


    • #3
      Re: Hearth Board Support

      I used plywood under my stand (and removed it after). It was inside of my forms and sagged a little in the back corner. This meant that the slab is a little bit thicker in that back corner. Not a big deal, but certainly nothing to reccomend about tha approach. I like dmun's approach. Overlap a little and just leave it in there.

      My Oven Thread:


      • #4
        Re: Hearth Board Support

        I used Hardibacker, cut to fit within the blocks. Probably had around a dozen temporary vertical supports with 3 horizonal 2 x 4 "beams" as support. My plan was to leave the Hardibacker in place after knocking out the supports. 3 yrs later...the Hardi is still bonded in place. I give it a few taps everytime I pull logs from under there, still solid sounding, no signs of of loss of adhesion.

        I'd say, go with whichever way seems easiest as long as you have plenty of supports to eliminate sags or a collapse.