web analytics
Setting a perlcrete pad despite the cold - Forno Bravo Forum: The Wood-Fired Oven Community


1 of 2 < >


Hello, Forno Bravo Community Forum members.

As many may have noticed already, the Community Forum site was briefly down today. While working on scheduled routine maintenance, we encountered an error when trying to add a software update. As the site is now back up and running, some of you may notice that some recent data has been misplaced from November 10th up to today. We are currently working on resolving the issue. The forum has full operational capabilities and we encourage all forum members to continue actively posting in the threads.

We apologize for any inconvenience that this issue may have caused you. The Forno Bravo family values each and every member of our community. If you have any issues or concerns, please feel free to let us know on our issues thread here:


Thank you for understanding.
2 of 2 < >

Forno Bravo Forum Thread Message

Hello, Forno Bravo Community Forum Members!

The Forno Bravo team has heard the feedback in regards to the community forum. We wanted to take the time to re-enforce our commitment to a fully engaged Forum with professional moderation.

Our top priority as a company is to fix all forum errors and issues that you are experiencing. As we are swiftly working on these problems, we want to say that we highly value the Forum Bravo Community Forum and every single community forum member.

We have set up this thread so that every member can address any concerns, issues and questions about the forum. Please feel free to ask whatever you would like in regards to the forum; let us know what issues you are experiencing so we can work on resolving them as fast as possible. However, we stress that we would like constructive engagement, so please be specific about the issue you are experiencing.

Thank you for all of your patience and continued support.

Link to topic: http://www.fornobravo.com/community/...with-new-forum
See more
See less

Setting a perlcrete pad despite the cold

  • Filter
  • Time
  • Show
Clear All
new posts

  • Setting a perlcrete pad despite the cold

    My plan has been to install a slab of perlcrete as the pad over which to build a pizza oven. The general method was to pour the perlcrete into a wooden form set on top of the firebricks off the ground. The bricks would have an old shower curtain over them to keep the cement from getting on to them. My assumption was after some cure time, I could remove the form, pull out a few bricks, get some hands under the thing, lift it up, and rest it down on top of my cinder block base with some mortar ready to go. I have not had much luck with this.

    In the first attempt I had used concrete instead of cement. After two weeks, I had something that crumbled apart right as I tried to pick it up. It would break off right at the corners. That's when I realized I should have been using cement. So I have tried again with a 1:6 ratio of Type I Portland cement to perlite. The slab is poured about 4.5" thick; that's about how much I had yielded when all was done. The pad is a square four feet to a side. There is also two meshes of rebar inside.

    The past few days, the weather got down to freezing overnight and there was some rain in the forecast. I had covered it over in a tarp for that whole time. I think it had gone roughly 24 hours w/o a tarp when the weather was still okay, then it got covered the night things were supposed to get bad. I think this will be the last freezing night. I checked the tarp and noticed a lot of condensation on it that I removed.

    What has me a little afraid is I found a small chunk not level with the risk that I managed to break off. I found I could bust that little piece in half just about the same way I could with the perlite and concrete, so I'm afraid I screwed this up again.

    I am wondering if this method is even possible, or if I should be doing something else to prepare the base for my oven. I can get more materials tomorrow before noon when the place here closes, and I'd want to use the weekend to get this right. Or if you guys think it needs to just cure some more in warmer weather, then I'll leave it alone.

    Given I already blew my first slab, I want to get this working right ASAP. I've had my firebricks and clay for awhile now just waiting to be used.

  • #2
    Re: Setting a perlcrete pad despite the cold

    The Pompeii Oven construction guide available free through Forno Bravo can provide you with some solid direction on how to pour a perlcrete slab. Have not seen someone try to pour the slab and then mortar it onto the base. Most slabs are poured in place using rebar to provide strength.


    • #3
      Re: Setting a perlcrete pad despite the cold

      I have not had much luck with this.
      I dare say.

      Insulating concrete has a lot of compressive strength, meaning it's hard to crush, but almost no tensile strength, meaning if you try to pick it up in one or two places it's going to fall apart, exactly as you have demonstrated. It's also going to do the same thing if you are trying to bridge a gap with the stuff. It has to sit on top of a rigid structure, like a reinforced concrete pad.
      My geodesic oven project: part 1, part 2


      • #4
        Re: Setting a perlcrete pad despite the cold

        It has to be poured in place, it is not movable, and you do not want or need any rebar/mesh in it.


        • #5
          Re: Setting a perlcrete pad despite the cold

          "I am wondering if this method is even possible,"

          No. Its not. You want, from the bottom up:

          1 Foundation or slab on grade.
          2 Walls
          3 Structural suspended slab of reinforced concrete.
          4 Perlcrete or vermicrete layer
          5 Hearth bricks.

          Do not allow any Portland based concrete or perlcrete to freeze while curing.
          Last edited by Neil2; 02-13-2011, 12:01 PM.


          • #6
            Re: Setting a perlcrete pad despite the cold

            A gentleman came into the store yesterday, and I could tell just by talking to him that it was Rocko. I think we got him lined out now on the pad and insulation, and how to form it.


            • #7
              Re: Setting a perlcrete pad despite the cold

              Yeah it's a small world after all. When I explained on the other side of the counter that I'm a moron and I'm trying to make a pizza oven, I think he figured it out.

              I spent the weekend preparing the slab on top. I had a bunch of fast-drying concrete I mixed with some Maximizer, and I'm kind of wondering if it's already cured. It was real hard just from curing overnight. I'm thinking I'll keep the support underneath until Friday but I'll probably start screwing with it Wednesday.

              Now I need to figure out what to do with that perlcrete pad I made. The first time I made a pad with 1:4 concreteerlite, the edges broke right off when I lifted them up, but the core of it was pretty strong. I had to break the center up by lifting it up and dropping it down onto my patio slab. This new pad is 1:6 cementerlite and might hold up a smidgeon better. I'm thinking of picking it up with a helper suspending it with two scraps of cement board for support and see if it'll survive the brief walk over to the concrete slab. With a little fresh perlcrete spread on the new pad, I am thinking I'll get the center part that matters to transfer and I can use a little fresh perlcrete to keep it all together.

              I assume if that fails I can bust it up, crush it back up, mix it with a little fresh perlcrete, and just pour it on top like I should have in the first place. I just don't want to mix up a huge bunch of perlcrete again. And I certainly don't want to just dispose the perlcrete I've already made.


              • #8
                Re: Setting a perlcrete pad despite the cold

                You can use the chunks for the new pad. It only has to have compressive strength, nothing else. Put the big ones in place and place the new around them, plus mix the smaller chunks in with the new mix.


                • #9
                  Re: Setting a perlcrete pad despite the cold

                  Oddly enough, the perlcrete slab held up when I picked it up and moved it. Some of the edges crumbled off, so I can see the problems with using it to span a space. But I was impressed with how we could walk it over to the concrete pad and slide it up on there without the whole thing just cracking in half. I had spread some fresh perlcrete under it to help bind it, and mortared the sides by mixing up some cement with the sand I had used to help level that original perlcrete slab.


                  • #10
                    Re: Setting a perlcrete pad despite the cold

                    Now that's a first!!!
                    Our Facebook Page:http://www.facebook.com/pages/Stoneh...60738907277443