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Homebrew cast over yoga ball

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  • #16
    david s
    Thx for a quick answer!
    i will try to add another layer tonight then.
    Do you think its safe to remove the sand today? its been 48 hours.

    After this layer i will wait atleast a week before i add my insulation, hope its workable enough with the rockwool, bought 45mm thick, maybe should go for 2 layers of that and make sure the joints arent at the same place


    • #17
      Think the second layer 8f homebrew was good, think it stuck really well to the existing layer.

      Added 90mm of rockwool and covered it with a thin layer of vermicrete. The vermicrete was a bit difficult to get to stick so I had to use a form for the lower part 8f the dome, and the thickness ended up around 2cm,a bit thin, but ran out of vermiculite.

      I want to get a nice finnish on the outside, and make it waterproof. Would also like it to be white.
      Thinking about mixing lime, sand and concrete and use that as a Finnish, or just sand and concrete. Opinions on this?
      Ratios to use?
      Would the lime solution be rain proof?
      Will add pictured later


      • #18
        Rockwool is difficult to vermicrete against. You’ve done well particularly with such a thin layer. I always do the drying fires before applying the stucco layer to avoid trapping moisture. If you want the outer stucco layer to be white then you will find that the cement wil make it grey unless you use white cement. A good mix is 4 parts sand, one part cement, one part hydrated lime. This mix is not waterproof but you can always paint it white with an acrylic paint to make it waterproof. Personally I think white is a mistake as there will be some soot falling from the flue cap to dirty it up. I usually apply the stucco in one single layer about 15 mm thick and mix in AR glass reinforcing fibres due to time constraints , but most do two layers over chicken wire, 24 hrs apart. A wet sponge over the surface will even out any trowel marks, Holding moisture in that outer stucco layer for a week will enhance its strength. I do this by wrapping the whole oven in cling wrap.
        Last edited by david s; 07-20-2018, 01:13 PM.
        Kindled with zeal and fired with passion.


        • #19
          Thx for all the help david s I will try the 1:4:1 mix and try it. Thought about leaving a 100mm circle on the top, let everything dry, then cover the hole with cling wrap and make a hat out of the cement:sand:lime so I can lift it if I need to eliminate water after a longer period of wet weather, you think that would work? Paint it with some waterproof color later.

          The AR glass fibres aren't the same as the polypropylene fibres used in the homebrew?


          • #20
            I like to do the drying fires after insulation before proceeding to the outside render. This reduces the possibility of steam pressure build up cracking the outer shell. Your vent plan seems sound. A removable hat should work well.if after around an hour of firing, your outer shell feels hot to the touch, then your insulation is wet. Under normal operation when the insulation is dry the outside will only feel cosy warm.
            Use the fine polypropylene fibres in theouter shell mix if you still have them, but they don’t impart a lot of flexural strength as they’re too fine. The give quite good compressive strength though. Remember to mix them about double the time that you’d think as they take a long time to disperse properly. The AR (alkaline resistant) glass fibres give good flexural strength. The guys who do GFRC countertops use them a lot for strength so go to them for sourcing. Very easy to work with.
            Kindled with zeal and fired with passion.