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Post by steve999 on May 23, 2016 22:07:56 GMT
Hi all.
I'm going to make my dome from brick, then I was gonna put vermiculite render over that, then loft insulation held down with chicken wire, with a smooth render finish. Will that be ok?
Thanks in advance, Steve.
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Post by oblertone on May 23, 2016 22:54:25 GMT
Loft insulation will apparently break down possibly leaving voids in your structure, insulating blanket is more expensive but does the job.
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Post by steve999 on May 24, 2016 7:59:27 GMT
Thanks Oblertone.
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bento
valid member
Posts: 88
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Post by bento on May 24, 2016 8:45:21 GMT
Hi all. I'm going to make my dome from brick, then I was gonna put vermiculite render over that, then loft insulation held down with chicken wire, with a smooth render finish. Will that be ok? Thanks in advance, Steve. From what I have seen, most put the the blanket straight on the dome, vermicrete on top, render finish on the vermicrete. From a structural point of view I think this would work best also. Vermicrete provides a good sturdy lightweight structure to render over, whereas rendering straight on to a blanket you only have the strength of one render coat seperating weather and the odd knock with your blanket, compared to render over vermicrete.
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Post by downunderdave on May 24, 2016 9:35:27 GMT
I used fibreglass ceiling insulation directly against the inner dome for my first oven built nine years ago. It had foil on one side which I faced to the outside, then chicken wired over it prior to render. From memory the fibreglass was around 3" thick. The problems I encountered were that the fibreglass insulation was not dense enough and tended to compress easily making the insulation space thinner. Secondly the foil also acts as a moisture barrier making drying the oven more difficult. I also used the fibreglass insulation under the floor which was held up by insulating firebrick props placed strategically. Contrary to subsequent advice about the binders in the insulation burning out, on deconstruction the fibreglass was fine, although it may vary from different manufacturers. Glass melts at around 900C well above any WFO temp so I can't see why there should be any problems, maybe try some flame tests on it.
I now prefer to use ceramic fibre blanket against the dome, then covered with a layer of 10:1 vermicrete which insulates well and provides a firm enough substrate to render over once set and dried.
I'd suggest if you are keen to use the loft insulation, maybe because it's free, that you cover it with a layer around an inch and a half of the 10:1 vermicrete which is light enough not to compress the loft insulation. If it is foil backed get a short plank with 3 or 4 nails protruding a little and slap the foil silly, better to do this operation after the chicken wire. This will allow moisture to pass the foil layer.
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stu
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Posts: 9
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Post by stu on Jun 5, 2016 21:33:20 GMT
Ok so I'm fast approaching the insulation stage, I have ordered the ceramic blanket and have chicken wire ready for the vermicrete layer, but my question is how much vermiculite will I need to get to make the vermicrete when the external diameter of my brickwork is approx 110cm?
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Post by downunderdave on Jun 6, 2016 2:50:27 GMT
That depends on how thick a vermicrete layer you want to have. Work out the volume required using 4/3 Pi x r3, What volume you lose in the door you need for around the flue so just calculate the volume of a total hemisphere. You lose around 20% of the dry vermiculite volume when you mix it with water and cement.
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