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How many layers of concrete on top of FB blanket around the dome will be needed?

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  • How many layers of concrete on top of FB blanket around the dome will be needed?

    Question about concrete around the insulation blanket on the dome.

    In the coming days I will wrap my new dome with 2 layers of FB blanket, but after that I'm confused. It's an outdoor pizzaoven.

    1) I don't know how many layers of insulating concrete that I need to have?
    2) Should the outer layer be a different kind of concrete? (I will finally put stuck on the outer layer)
    3) 100 l of vermiculite costs around 50 $ and leca nuts are maybe half the price. Can I use leca nuts?

    Kind regards


  • #2
    The leca aggregate I've used has spheres averaging around 10mm in it's not easy to get a workable mix to create a thin layer. I think you'd need to do a 3:1:1 leca, sand, cement mix to create a 1" layer than you could apply easily by hand. Alternatively a 10:1 vermiculite, cement mix works ok. Leca is dearer for me so I don't use as much of it. The thing I like about it is that the little spheres are harder on the outside than in the centres meaning greater strength for the given density.
    Kindled with zeal and fired with passion.


    • #3
      Hi Jesper,

      In Norway, you can buy different grades of Leca balls The company 'Leca' make insulation blocks using these leca balls. They also make a facade block using a finer grade with leca balls, if you can get your hands on some of this, I'm sure its the same in Denmark, you can combine it with the normal grade (half and half) which will fill the voids between the larger balls and be an easier fatter mix to work with. The more sand you use to fill the voids, the less insulation values. Like David says, its not easy to get a workable mix by only using 10mm balls. Leca concrete is a good insulator, and is also strong,



      • #4
        Hi David.

        Thank you for your answer to my question regarding concrete with insulation for the dome. I'm til confused about the ration between vermiculite and concrete. I finally got bags of vermiculite.

        I will put an 2 layers of FB blanket on the dome - and the concrete. In your answer to me, you described a ration 1:10 (concrete - vermiculite), but several sites are talking af bout a ratio of 1:5. Du you still go for 1:10?

        The outer most layer should that be different to resist weather?

        Kind regards



        • #5
          You need more strength under the floor so generally a 5:1 ratio is better there. Over the dome you only need enough strength to render an outer shell onto. The more cement you add the less insulating the mix becomes.i find a 10:1 is about as lean as you can make it while still maintaining a reasonably workable mix.
          Kindled with zeal and fired with passion.


          • #6
            Okay - that makes sense. Thanks


            • #7
              Before dome insulation - "Go live" next weekend :-)