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Drying out vermicrete hearth insulation slab - Forno Bravo Forum: The Wood-Fired Oven Community

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Drying out vermicrete hearth insulation slab

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  • Drying out vermicrete hearth insulation slab

    Hi, im just about ready for the vermicrete hearth insulation. Its sitting on a concrete slab and surrounded on 4 sides by blockwork. I'm wondering about letting it dry out in this climate(Wet!) Do I need to keep it covered, maybe build a flat roof out of ply over it or something? Obviously with normal concrete we just leave it exposed and it dries with time but from reading here I may need to keep this stuff covered and it needs a week of drying before i can sit the oven on it?
    I'm also thinking for building the dome insulation that I may need to do the same?

    Thanks

    R

  • #2
    Re: Drying out vermicrete hearth insulation slab

    Do keep it covered. Even after it is cured this stuff will soak up water like a sponge. You can cover it with a raised tarp to keep the rain out but allow air to circulate. A temporary ply wood lean-to would help. I started out with a tarp, then a tent and a tarp. I ended up building a permanent shed over my build.
    Its sitting on a concrete slab and surrounded on 4 sides by blockwork.
    I'm a little intrigued by that statement. I think that you might need to include some weep holes at the base of those blocks to have another escape route for some of this and any future water problems. Now is also the time to think about a moisture barrier between the concrete hearth and the insulation.

    Can you post a pic of what you have completed so far?
    I don't care what folks say behind my back........They are either braggin' or.......lyin'

    joe watson

    My Build
    My Picasa Web Album

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    • #3
      Re: Drying out vermicrete hearth insulation slab

      Originally posted by Gulf View Post
      Do keep it covered. Even after it is cured this stuff will soak up water like a sponge. You can cover it with a raised tarp to keep the rain out but allow air to circulate. A temporary ply wood lean-to would help. I started out with a tarp, then a tent and a tarp. I ended up building a permanent shed over my build.

      I'm a little intrigued by that statement. I think that you might need to include some weep holes at the base of those blocks to have another escape route for some of this and any future water problems. Now is also the time to think about a moisture barrier between the concrete hearth and the insulation.

      Can you post a pic of what you have completed so far?
      I will Gulf. Im in the US as the moment but will be home on monday. I'll post a pic then. Hadnt considered weep holes or a moisture barrier.... I could drill vertically down through the slab in a few places I suppose. What would be the prupose of a moisture barrier at this point, wouldnt that just cause my vermicrete layer to retain any moisture? or is it against moisture wicking its way upwards? I did place a moisture barrier in the foundation of the base slab that the walls sit on.

      Thanks

      Richard

      Comment


      • #4
        Re: Drying out vermicrete hearth insulation slab

        Originally posted by RichC View Post
        I will Gulf. Im in the US as the moment but will be home on monday. I'll post a pic then. Hadnt considered weep holes or a moisture barrier.... I could drill vertically down through the slab in a few places I suppose. What would be the prupose of a moisture barrier at this point, wouldnt that just cause my vermicrete layer to retain any moisture? or is it against moisture wicking its way upwards? I did place a moisture barrier in the foundation of the base slab that the walls sit on.

        Thanks

        Richard
        Richard,
        You nailed it. When building, we need to attempt to consider two future problems. Water wicking from the stand upward, the possibility of rain being blow in the door, or a failure of the render/cover.
        That maybe actually three problems, but rednecks ain't expected to count correctly . The moisture barrier (plastic, paint etc.) is cheep insurance. The weep holes may be added like you suggested. Not knowing exactly what you have started and your finished build will be, I have to give you all of the negatives. The pics will help .
        I don't care what folks say behind my back........They are either braggin' or.......lyin'

        joe watson

        My Build
        My Picasa Web Album

        Comment


        • #5
          Re: Drying out vermicrete hearth insulation slab

          Hi Gulf,
          Here's what I've done to date. The slab is only 50mm below top of the wall at the moment so I've to raise up the wall a little . I'm thinking of using red brick which will give me a total depth of about 120mm for vermicrete insulation. When the vermicrete is done ill build the oven on it and then after insulating the oven I intend pouring a concrete countertop around the whole thing which will be polished. After the countertop is poured ill put a weather proof render over the oven. I intend for the countertop to slope slightly away from the centre on all sides and to overhang the block work. What to you recommend or think if my plan?
          Thanks
          Richard
          Attached Files
          Last edited by RichC; 06-24-2013, 12:55 PM.

          Comment


          • #6
            Re: Drying out vermicrete hearth insulation slab

            In case you can't quite make it out, another photo
            Attached Files

            Comment


            • #7
              Re: Drying out vermicrete hearth insulation slab

              [QUOTE=Gulf;155706]Richard,
              You nailed it. When building, we need to attempt to consider two future problems. Water wicking from the stand upward, the possibility of rain being blow in the door, or a failure of the render/cover.
              That maybe actually three problems, but rednecks ain't expected to count correctly . The moisture barrier (plastic, paint etc.) is cheep insurance. The weep holes may be added like you suggested. Not knowing exactly what you have started and your finished build will be, I have to give you all of the negatives. The pics will help .[/QUOTE

              There is a fourth problem area for water intrusion if you have a flue pipe and that is where the outer shell meets the flue pipe. I guess also the chimney cap is another area. I know mine gets a bit of water in there when stormy weather drives rain horizontal. I also believe that dry porous refractory and thirsty vermicrete will take on moisture from 100% humidity if it's for a fair length of time. It never hurts to fire up your oven in these conditions, just to help dry it a little.
              Kindled with zeal and fired with passion.

              Comment


              • #8
                Re: Drying out vermicrete hearth insulation slab

                Originally posted by RichC View Post
                Hi Gulf,
                Here's what I've done to date. The slab is only 50mm below top of the wall at the moment so I've to raise up the wall a little . I'm thinking of using red brick which will give me a total depth of about 120mm for vermicrete insulation. When the vermicrete is done ill build the oven on it and then after insulating the oven I intend pouring a concrete countertop around the whole thing which will be polished. After the countertop is poured ill put a weather proof render over the oven. I intend for the countertop to slope slightly away from the centre on all sides and to overhang the block work. What to you recommend or think if my plan?
                Thanks
                Richard
                I like the term "weatherproof" . I assume that you are planning an Igloo? I love the Igloo look. An uncovered igloo can raise some problems though. Like the two that I mentioned, the third that I couldn't count ,. The fourth that David brought will be a problem no matter your finished oven style.
                If you can keep your oven dry, through out the build, you may not need the weep holes. If not, adding a thin layer of concrete and forming a low spot where you can collect the water, and route it to the outside would help. A moisture barrier on top of this layer would be great! When considering "weather proof renders", you will definitely need to include some type of vent.
                I don't care what folks say behind my back........They are either braggin' or.......lyin'

                joe watson

                My Build
                My Picasa Web Album

                Comment


                • #9
                  Re: Drying out vermicrete hearth insulation slab

                  Yes it's an igloo. How does the 'vent' work with this? Does that assume there's an airgap between the insulation and the external render? How is that achieved?

                  Thanks

                  Richard

                  Comment


                  • #10
                    Re: Drying out vermicrete hearth insulation slab

                    Originally posted by RichC View Post
                    Yes it's an igloo. How does the 'vent' work with this? Does that assume there's an airgap between the insulation and the external render? How is that achieved?

                    Thanks

                    Richard
                    The air spaces between the vermiculite grains provide the air space, but you must make the brew lean to achieve this. I use 10:1. Also don't compact it too much.
                    Kindled with zeal and fired with passion.

                    Comment


                    • #11
                      Re: Drying out vermicrete hearth insulation slab

                      Originally posted by david s View Post
                      The air spaces between the vermiculite grains provide the air space, but you must make the brew lean to achieve this. I use 10:1. Also don't compact it too much.
                      Thanks David. That's 10vermiculite to 1 cement? I assume it still has the strength to hold the done shape? Do you use any chicken wire or mesh of any sort in the structure to help it hold shape?
                      Thanks
                      Richard

                      Comment


                      • #12
                        Re: Drying out vermicrete hearth insulation slab

                        Originally posted by RichC View Post
                        Thanks David. That's 10vermiculite to 1 cement? I assume it still has the strength to hold the done shape? Do you use any chicken wire or mesh of any sort in the structure to help it hold shape?
                        Thanks
                        Richard
                        Yes, 10 vermiculite 1 cement. I mix it dry and add 3 parts water. No mesh.
                        Kindled with zeal and fired with passion.

                        Comment


                        • #13
                          Re: Drying out vermicrete hearth insulation slab

                          Hi Guys,
                          Ive started putting in the vermiculite hearth insulating layer. I'm keeping if covered and intend covering it with a polished concrete countertop after the dome and dome insulation goes on. Then the last step will be the (hopefully) 'weatherproof' render for the dome. this should allow water to run down the dome and off the polished concrete countertop. although I'm trying to keep it covered, in my damp, windy climate the vermicrete is definitely going to hold some moisture. I think I'm going to drill down through it in the 4 courners and the centre to create 5 weep holes as Gulf recommended. Ive only about 60mm of vermicrete down so far, so the holes will fill with vermicrete when I finish the insulating layer off.
                          My worry is that it'll be sealed when the concrete countertop goes on so how will it dry out when firing? How does moisture evaporate away or does it just happen because nothings 100% waterproof anyway??
                          Also, I was thinking of putting a layer of plastic between my concrete countertop and the vermicrete slab to prevent any water getting back into the vermicrete from the top. Would this be counterproductive when drying out? Good or bad idea?

                          Thanks!

                          Richard

                          Comment


                          • #14
                            Re: Drying out vermicrete hearth insulation slab

                            Richard,
                            Your fires will eventually dry the stuff out, but it may take months.mThat's why I believe it's better to lay the stuff in layers with a week between each to let the sun and wind dry it out somewhat (but keep out the rain) The water eventually finds its way out. It will migrate back to the porous floor bricks a little between each firing. Try to slope your countertop away from the dome to discourage entry where the dome meets the countertop.Adding an admixture to make the countertop waterproof will also help, alternatively your plastic sheeting barrier will achieve the same.
                            Dave
                            Last edited by david s; 08-09-2013, 12:59 PM.
                            Kindled with zeal and fired with passion.

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