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Vermiculite vs perlite for insulation under the oven floor - Forno Bravo Forum: The Wood-Fired Oven Community

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Vermiculite vs perlite for insulation under the oven floor

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  • Vermiculite vs perlite for insulation under the oven floor

    Hey guys

    I've been reading a lot on this forum learning new stuff as I go!

    So far I have build my base and concrete hearth, I'm planning a 30" diameter dome 16" or so height with the relative sized opening blar blar. Anyways after some weeks it's coming on nicely but this is the first time I've built anything ever so I'm learning from my mistakes as I go.

    One thing I don't want to cock up is my insulation layers. I'm pretty sure I've got the dome insulation situation nailed but I'm at the stage of pouring my 4" perlite or vermiculite mix insulation layer.

    So my main question is which is better/easy to use/more durable/cheaper vermiculite or perlite mix (assuming 5:1 cement mix)?
    I understand they both have the same insulating properties.

    My progress so far can be seen here:
    Mike Suttie's Photos - Pizza Oven Construction!!! | Facebook

    Cheers guys

  • #2
    Re: Vermiculite vs perlite for insulation under the oven floor

    I didn't use vercumilite or perlite for the floor insulation; I used a 2" ceramic insulation board. I did put a 4" dome insulation of perlite and portland cement on the oven. I read on one of the posts that perlite will break down more than vermiculite during mixing, but I don't know how it differs from vermiculite as far as compressive strength is concerned once mixed and cured. Perlite was more readily available than vermiculite and was about $2.25 USD per cu ft.

    Your build is looking good.
    My WFO project: http://picasaweb.google.com/stevprin/WFOSmallPhotos#

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    • #3
      Re: Vermiculite vs perlite for insulation under the oven floor

      From what I have observed from the two, there is really not much difference in performance. I was a bit surprised with the perlcrete's compressive strength considering how light perlite was (using 5:1 ratio). Like most people, you can tell when the perlite is properly coated with cement better than vermiculite since perlite is white. You can go with higher ratios like 8:1 or even 10:1 to increase insulation performance without suffering much loss in compressive strength. You do suffer in terms of bond strength. The perlcrete is like rice crispies and the grains chip off easily at higher ratios. I applied a concrete border to the sides of the insulating perlcrete to keep it from crumbling.

      I think your decision will be based more on the availabilty and price in your location. But if you have money to burn, I suggest you go for the more high tech insulation boards. They are much more efficient and less messy to install.
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      • #4
        Re: Vermiculite vs perlite for insulation under the oven floor

        Awesome thanks for your response. Yea I was wondering about the compression strength given how light that stuff is! I was looking at Perlite and it's dirt cheap but I really don't want my oven raised by another 4" so may have to invest in 2" of ceramic board stuff like you say.

        "Your build is looking good."
        Cheers Steve! Although this is my first building experience ever so it is far from elegant! The next one will be something special haha.

        Cheers for your help guys

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        • #5
          Re: Vermiculite vs perlite for insulation under the oven floor

          Raffy,
          excellent post. This one should have been in bold.The perlite is marginally better in insulation value , but is trickier to handle (dust and abrasion degradation) I prefer vermiculite.
          Kindled with zeal and fired with passion.

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          • #6
            Re: Vermiculite vs perlite for insulation under the oven floor

            Originally posted by mikesuttie View Post
            So my main question is which is better/easy to use/more durable/cheaper vermiculite or perlite mix (assuming 5:1 cement mix)?
            I made a 4" thick layer of vermiculite and mixed it 7:1, after the third day i was worried about the strength of it because i could press it down quite abit. After about a week it became really hard.

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            • #7
              Re: Vermiculite vs perlite for insulation under the oven floor

              After enquiring about the CF board stuff it really is going to push my budget over the top plus i'll need it cut delivered etc so looks like i'll have to modify my design a bit and get some perlite.

              Ok this may sound stupid but is the 5:1 ratio done by mass or by say heaped quantity(shovel load!) I.e for every kg of cement it's 5 kgs of perlite ??

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              • #8
                Re: Vermiculite vs perlite for insulation under the oven floor

                Hi,

                I just finished my insulation layer, I had a one gallon bucket and a 2 gallon bucket and used about a 6 to one ratio. 3- 2gallon buckets of perlite to 1 gallon bucket of portland cement. I folded the dry together and then folded in the water gently. I made relatively small batches 6 gallons of perlite and one gallon of cement. It has been two days and it is setting up well. Wear mask while mixing, a little dusty.


                Derk

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                • #9
                  Re: Vermiculite vs perlite for insulation under the oven floor

                  Cool sounds good Derk! How long will you give it before building on top of it?? God I really want to get my dome built!! Will have to keep myself occupied with rendering (stucco or whatever you guys call it! lol) the walls while I wait for perlite mix to set.

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                  • #10
                    Re: Vermiculite vs perlite for insulation under the oven floor

                    Ok this may sound stupid but is the 5:1 ratio done by mass or by say heaped quantity(shovel load!)

                    By volume. Five shovels of vermiculete/perlite to one shovel of portland cement. Water volume as required. (Exact water volume cannot be specified since it may vary depending on relative humidity and any existing water that may already be in your perlite.)

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                    • #11
                      Re: Vermiculite vs perlite for insulation under the oven floor

                      I have learned from other posts to give it a good time to set up. I have a bathroom and a roof to replace so mine will probably set for a good week or so. It gets better and better as time passes, so be patient.

                      Derk

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                      • #12
                        Re: Vermiculite vs perlite for insulation under the oven floor

                        If you can wait it certainly won't hurt to do so, but if you are impatient you can do it it the next day like I did. I did wet set the floor in mortar though.

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                        • #13
                          Re: Vermiculite vs perlite for insulation under the oven floor

                          It is important to get the water content right. There is a tendency to add too much which results in an uneven mix. It needs approximately double the quantity of water that normal concrete requires. I've found that for every 10 parts of vermiculite by volume you need 3 parts water.
                          Kindled with zeal and fired with passion.

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                          • #14
                            Re: Vermiculite vs perlite for insulation under the oven floor

                            Tom,

                            What was your recipe for your floor setting mud? I have fireclay and #40 mesh sand to use.

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