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Weep hole and FB board placement

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  • Weep hole and FB board placement

    I've seen some builds where the FB board is just under the oven floor and not under the soldiers, dome insulation, etc. I'm going to put tile sheets under the FB board in order to help drain water. If the FB board is only under the oven floor, the insulation blanket around the dome will be touching the concrete slab hearth and will be able to absorb water. Therefore, should the tile sheets and FB board be under the entire dome (oven floor + soldiers + several inches to account for the dome insulation/mortar)?

    In my attached drawing I have 2 cross sections where you can see in #1 the FB board is only under the oven floor. In #2 it is under the entire oven dome. Depending upon the answer to where the FB/tiles extend to, where do I put the weep holes, and how many are needed?

    I would think you would want weep holes on the outer rim of the dome, where the insulating blanket will be, in order to keep water out of it. Is that a correct assumption? I would think to put maybe 10 or so weep holes evenly spaced, roughly like I show in the third, birds eye view drawing attached. Thoughts?
    My 36" build -&- Youtube Timelapse

  • #2
    All parts of the dome and floor MUST be isolated from the concrete hearth by insulation. If the dome is placed on the hearth, the heat of the dome is transferred down through the hearth which acts as a heat sink. 3-4 weep holes should be good, with wire mesh siliconed to underneath to keep bugs out . As you proposed, tiles under the CaSi board is a solution so water can egress out through the weep holes. Gap the tiles so there are channels to the weep holes.

    Also, full soldiers may require buttressing due to the outward pressure caused by the dome and arch and top of soldier joint.
    Google Photo Album []


    • #3
      Thanks, I knew what I had seen was fishy.

      Any suggestions on where to place the weep holes? Also, should I apply some sort of adhesive between the tiles and the hearth (caulk/mortar?) or is the weight of the dome sufficient?
      My 36" build -&- Youtube Timelapse


      • #4
        Low spots if any otherwise water typically migrates from the outside of the dome in. No need to set tiles with thinset or mortar. These ovens are heavy.. Consider 1/2 soldier or 1/2 header for your first course to minimize outward force of dome. Click image for larger version

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        Google Photo Album []


        • #5
          Ok - totally new to this and about to start my build! YIKES - terrifying to see so many mods to the Forno Bravo plans that they seem almost redundant! As I try to wrap my head around what to do for the floor of the oven I see this set of posts re: tiles and weep holes (neither mentioned in Forno Bravo design) - so what are they?! Are you putting tiles (what kind? size? configuration?) under the 2" fibre board? and are you drilling holes under the floor in the spots you noted to allow water to seep out?

          I really need some advice here.

          I have seen everything from just put the hearth down, 2" fibre board, then firebrick floor and build (Forno instructions) to 4" of percrete, then the FB and brick floor. Then this - with the tile (what kind?) and holes in the hearth for drainage .

          Wow - I'm really confused - help!?
          You are welcome to visit my build HERE


          • #6
            I’m in the same situation as Baza. I have downloaded the FB plans and just assumed that laying the CaSi board down and placing the floor tiles on top was the way to go.

            Being in the UK there is always rain around the corner so should I look at putting weep holes into my concrete hearth or should I be putting something else under the CaSi board?

            My dome will be outside the floor so the CaSi board is going to be as wide as my external diameter with an exposed igloo design I was just going to render over the CaSi board after the blanket is attached and Vcreted. Is this correct?


            • #7
              Weep holes provide a means for any water that gets in can get out otherwise it just sits there and may be absorbed by the CaSi board.
              Google Photo Album []


              • #8
                Chobbs and Baza

                I'll let others comment on my work, but I found a bunch of old tile in my basement, broke it up (it was like 12x12" so a little too big) and then scattered it about under the floor. Then I randomly drilled 4-5 holes through the slab. Then I cut up some old screen I found in my basement too, and draped it over the holes (to prevent bugs from getting in apparently). I just used the weight of the tile chunks to secure the screen in place.

                I have arrows pointing to the dark spots where I put the screen and weep holes (sorry I didn't take a birds eye view). In the other pic, you can see where I laid out some other tile I found, but I didn't have enough of it. I think the recommendation on this forum is to get the mosaic tile sheets and lay those down. I wish I would have had a little more tile, mines a little spacious but I had already run to the hardware store several times and thought it would be fine as is. Click image for larger version

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                My 36" build -&- Youtube Timelapse


                • #9
                  plastered Thanks for the quick reply.

                  My order of CaSi board and bricks should be coming soon so will still some holes tonight and grab some tiles!

                  Thanks again.


                  • #10
                    UtahBeehiver is the KING!! Wow - thanks lads - excited for you plastered (great handle by the way!). And good luck on your next steps Chobbs! plastered thank you for the pics and explanation. I’m wondering if this is a step I have to do given I will be building an enclosure for my oven? Or is this just good practice no matter what the finish? Sorry the newbie questions!
                    You are welcome to visit my build HERE


                    • #11
                      Regarding the placement and order of layers for the oven, I've added two links below that had particularly good diagrams/pictures of the updated recommendations from the forum folks. The free forno bravo plans definitely are out of date in some respects. A lot of innovations have been developed by forum members and the plans are now simply give you a good overall view of some basic build types to consider with good background info. Remember that the original basic (ancient!) Roman & Tuscan designs are still's just that now we have much better materials and techniques that improve upon the original designs (insulation materials for example).

                      Hope the build links below are useful to your understanding of the current recommended "upgrades"...



                      p.s. Water/moisture is a constant issue to all WFO owners. Even though you do everything absolutely correct, water seems to poke it's ugly head into the system somehow even when you build an outer structure to protect the oven from the elements...hence, including the screened weep hole, tile to lift the insulation board off the concrete hearth, and the addition of some sort of top insulation venting are best practices for building a WFO. One of those "Ounce of prevention is worth a pound of cure." issues.
                      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


                      • #12
                        SableSprings Thank you! Yes - water is as necessary to life as it is insidious in a build! Thank you for the help and guidance here! I appreciate the support of the builders here to outline not only a problem but incentive and creative solutions! Off to get some tile!! (Just dug my first foot of foundation hole - 3’ more to go - damn frost line!!)
                        You are welcome to visit my build HERE


                        • #13
                          This is a very helpful thread. Thank you for sharing.

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                          • #14
                            If I just use 4” of vermicrete/peri Crete on the entire hearth, do I still need weep holes and/or tile underneath? Or is that just for this FB board?


                            • #15
                              If I just use 4” of vermicrete/peri Crete on the entire hearth, do I still need weep holes and/or tile underneath? Or is that just for this FB board?
                              In my honest opinion, yes. However, it does present some problems that I haven't seen tackled to my liking. On the Simmental Farm 36" we were going to do just that, but the owner found enough free CalSil to have 4.5" of floor insulation. Had we have used the vermicrete, we were going to place a layer of window screen wire on top of the mosaic tiles and then a thin layer of landscape fabric on top of that.Next, we were going to place a thin layer of 5 to 1 vermicrete (with as little water in the mix as we could get away with) in the form. After that set we were going to proceed with the rest of the pour still with as little as we could. That should have worked to keep the spaces, grooves and weep holes open.
                              Last edited by Gulf; 01-13-2023, 01:15 PM.
                              Joe Watson " A year from now, you will wish that you had started today" My Build Album / My Build