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Exterior Dome Finish - Forno Bravo Forum: The Wood-Fired Oven Community

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Exterior Dome Finish

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  • Exterior Dome Finish

    Quick question.

    I am going to be using a ceramic blanket on my dome - should have 2 inches or more, depending on coverage. I will then place some 1 inch galvanised chicken wire over this and cap this off with a cement/ perlite or vermiculite mix to about 2-3 inches.

    my question is which is better verm or perlite for the top layer, and is it then weather-proof, or will I need to do a final concrete/ stucco layer over this?


    thanx in advance

  • #2
    Re: Exterior Dome Finish

    Originally posted by builder brad View Post
    Quick question.

    I am going to be using a ceramic blanket on my dome - should have 2 inches or more, depending on coverage. I will then place some 1 inch galvanised chicken wire over this and cap this off with a cement/ perlite or vermiculite mix to about 2-3 inches.

    my question is which is better verm or perlite for the top layer, and is it then weather-proof, or will I need to do a final concrete/ stucco layer over this?


    thanx in advance
    \
    Either is fine. I prefer verm because I think it is easier to work with.
    As for waterproof- Nope
    You will have to stucco it. Or cover it with a structure.

    I would also go with a little more than 2-3 inches of vermcrete.
    I have about 1 inch of blanket and 6-8 inches of perlite and verm all over my dome, but it's loose, no cement. Then that is covered with an inch of mortar and finally stucco.

    Even with that much insulation . I can still find warm spots at times.

    But the oven will usually stay hot enough to cook up to 48 hours + after one pizza firing.



    Dave
    Last edited by asudavew; 08-08-2008, 01:58 PM.
    My thread:
    http://www.fornobravo.com/forum/f8/d...ress-2476.html
    My costs:
    http://spreadsheets.google.com/pub?k...Xr0fvgxuh4s7Hw
    My pics:
    http://picasaweb.google.com/dawatsonator

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    • #3
      Re: Exterior Dome Finish

      Cheers Dave!

      Comment


      • #4
        Re: Exterior Dome Finish

        I just looked at your thread, nice work!

        reading your previous posts - I thought that you said perlite was easier to work with for the outer coating, not vermiculite? - I really want to learn from other peoples experiance and save myself time and effort.

        regarding the overall insulation layer for my oven I propose around 3 inches of blanket minimum plus 2-3 inches of perl/verm concrete mix. 48 hour cooking would be great. I plan to build a really tight fitting door using some 2 inch ceramic insulating board that I have left over with Walnut decorative fittings. Hopefully the insulating board will keep the heat away from the Walnut! and I will be able to seal the dome really well.

        Brad

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        • #5
          Re: Exterior Dome Finish

          Vermiculite vs. perlite.....I used both, verm. for the insulating slab and perlite for the dome; as for workability and consistency of the mix I don't have a preference.
          The only thing I found different was the "dry, out of the bag" consistency. The perlite granules were of a more consistent size all the way through each bag. The vermiculite seemed to be about 25% dust - at the bottom of each bag; as Les put it - seemed like very fine sawdust, I guess he found the same to be true. I would definitely recommend getting the course grade (if you can find it) as opposed to the medium (which I used) horticultural grade.

          RT

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          • #6
            Re: Exterior Dome Finish

            I used 2" of the Forno Bravo insulation, then 2" - 3 " of vermiculite/portland mix, then 2 layers of stucco. Seems to be very waterproof so far, I cooked 12 pizza's in a great rainstorm thursday eve, no problems. The outer dome doesnt feel warm for hours with the insulation that I used, and holds the heat for a whole day for cooking. We are still experimenting, but we've cooked about 85 pizza's since the 4th of July, with a few other attempts at a few other things... Bottom line - the ceramic insulation will make or break the project, more is better, 2 layers of the 1 inch is working great, double would be the best I'm guessing.....Good Luck, Jim

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            • #7
              Re: Exterior Dome Finish

              Originally posted by Derocherconstruction View Post
              I used 2" of the Forno Bravo insulation, then 2" - 3 " of vermiculite/portland mix, then 2 layers of stucco. Seems to be very waterproof so far, I cooked 12 pizza's in a great rainstorm thursday eve, no problems. The outer dome doesnt feel warm for hours with the insulation that I used, and holds the heat for a whole day for cooking. We are still experimenting, but we've cooked about 85 pizza's since the 4th of July, with a few other attempts at a few other things... Bottom line - the ceramic insulation will make or break the project, more is better, 2 layers of the 1 inch is working great, double would be the best I'm guessing.....Good Luck, Jim
              I am using a ceramic blanket in conjuction with coal ash in walls (Rado uses coal ash) so what steps do I take to cover the blanket with coal ash so that it will not pack the blanket down and could I then cover the blanket/coal ash with stucco. Is stucco waterproof enough for an oven and what is the ingredients and mix.

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              • #8
                Re: Exterior Dome Finish

                Coal ash? Isn't that a heavy dirt-consistency substance? I have heard of using wood ash, which is at least light and fluffy as long as you keep it absolutely, completely dry, but coal ash? Seems like more thermal mass to me.
                My geodesic oven project: part 1, part 2

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                • #9
                  Re: Exterior Dome Finish

                  I don't know what coal ash is either Plowry. The vermiculite/portland mix is light though, and it was put on over the insulation..... 2" of fb ceramic insulation, then chicken wire over the insulation, then the vermiculite/portland mix. There are several different mixtures for the outer stucco mix if you search the forum, depending on the area you are from, and the local ingredients available. I see you are from Australia, so maybe someone in your area will have a local recipe with local ingredients/techniques.. Vermiculite is very reasonably priced here in Michigan, as is the portland cement. These worked well for me... Jim

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                  • #10
                    Re: Exterior Dome Finish

                    Juste googled coal ash and read several articles.
                    What I found:
                    1) By product of coal burning (mainly from power plants)
                    2) Can contain any/ or all of the following - limestone, aluminum, silica, clay.
                    3) Generally contains heavy metals, selenium, arsenic, mercury - and very likely in high concentrations.
                    4) 3 basic types: Fly Ash - the finest (like dust), can be used as a portland substitue in concrete, bonds well and adds strength. Bottom Ash - has a sand like consistancy and can be used as a sand substitue in construction. Boiler Ash - coarser than Botton Ash, used in asphalt roof shingles, snow/ice control on roads, sandblasting grit, and asphalt for roadways.

                    Not sure why Rado would be using this stuff, other than an over abundance in his local area...not to mention, I found nothing that recommends it as an insulator. I think portland, sand, perlite, and vemiculite are much easier to locate for most oven builders - based on EPA regulations, I don't think this stuff is readily available in the US to people outside of industry.

                    RT

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                    • #11
                      Re: Exterior Dome Finish

                      Fly ash is one of the main ingredients in castable refractory materials and tends to make any mixtures more thixotropic, but have no idea of its advantages in an insulation mix. Ask Rado.
                      Kindled with zeal and fired with passion.

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                      • #12
                        Re: Exterior Dome Finish

                        now we are getting somewhere...a refractory use.
                        David, how readily available is this stuff in Australia? None of us yanks in the US seem to know much about it. I found more information on the proper handling and disposal than I did on actual uses. From what I found, depending on the type, it is a suitable substitute for sand and portland cement. It just isn't something we can go to the local building/masonry supplier and purchase.

                        If anyone knows Rado, ask him why he uses this as part of his insulation......enquiring minds would like to know.

                        RT

                        Comment


                        • #13
                          Re: Exterior Dome Finish

                          We have a electricity power station 300km north of Adelaide at Port Augusta which burns a poor grade of brown coal.
                          A mate of mine (worked with him for 25 years) use to drive a semi tanker up there to collect 24+ ton of the 'coal ash' which was still hot, very fine and was added to Portland cement (to make 'blended' cement) and was called fly ash'.
                          I used to do the occassional trip with him for company.
                          I would not use it as it will increase your thermal mass and not insulate!

                          Neill
                          Prevention is better than cure, - do it right the first time!

                          The more I learn, the more I realise how little I know


                          Neill’s Pompeiii #1
                          http://www.fornobravo.com/forum/f8/n...-1-a-2005.html
                          Neill’s kitchen underway
                          http://www.fornobravo.com/forum/f35/...rway-4591.html

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                          • #14
                            Re: Exterior Dome Finish

                            If you are interested in this topic, then research geopolymers. Quite facinating, I have done some experimentation with different mixtures years ago, but not much recently.
                            Kindled with zeal and fired with passion.

                            Comment


                            • #15
                              Re: Exterior Dome Finish

                              Given the amount of coal that is burned in power stations, there must be mountains of the stuff to get rid of. I used to do quite a bit of experimentation using wood ash as a major ingredient of stoneware glaze for pottery. The trouble with the wood ash is that its composition is quite different depending on the type of wood used. Ash contains varying amounts of silica alumina and flux and you have to test each batch. This might be getting a bit off topic, but might also help in the use of the material for our purposes. By the way don't worry about the flux aspect, stoneware matures above 1200 C and would not create any problems for our (low) temps.
                              Kindled with zeal and fired with passion.

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