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Old 02-09-2014, 07:02 PM
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Default Thickness of vermiculite concrete

Hi everyone,

Aside from losing some insulation properties, do you think a 2 inch layer of vermiculite concrete will have enough compressive strength to support the oven etc... Made a minor height calculation error and don't want to go too high. And am trying not to spend 300 bucks on insulating board which is 2 inches thick.

I figure if it's going to hold, then I don't mind losing a bit of insulation. Can also put some sisulation under and maybe even in it to add extra insulation properties?

Thoughts?
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Old 02-09-2014, 07:22 PM
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Default Re: Thickness of vermiculite concrete

G'day
It's not its compressive strength that any is problem. 100 mm/4ins of pearlite cement is worth 50mm/2 ins of ceramic board or blanket in its insulation value.
Above all insulated. Find the extra 50 mm/ 2 ins pearlite cement if you can
Regards dave
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Last edited by cobblerdave; 02-09-2014 at 07:55 PM.
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Old 02-09-2014, 07:57 PM
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Default Re: Thickness of vermiculite concrete

2 inches of vermiculite is not near enough insulation. Buy the CF board. With all the work you are going to put into the dome, the cover, etc - You will regret not spending the $300 later when your floor and oven will not stay hot for very long.
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Old 02-09-2014, 08:12 PM
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Default Re: Thickness of vermiculite concrete

Increase your insulation and raise your floor to correct the error. You do not want to cut this corner. You can skimp on the dome insulation but the hearth is a massive heat sink.
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Last edited by Les; 02-09-2014 at 08:15 PM.
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Old 02-09-2014, 08:29 PM
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Default Re: Thickness of vermiculite concrete

might have to be board then...50mm board will be sufficient insulation then? dont want to go 100mm of vermiculite concrete so i guess board it is...dang!
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Old 02-09-2014, 10:25 PM
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Default Re: Thickness of vermiculite concrete

Sisalation sitting against a conductive material like concrete renders it pretty much useless. It has to have plenty of air around it to work. embedding a layer in the vermicrete slab would be better, but it will then act as a vapour barrier and make drying the vermicrete really difficult. i'm with the others either more vermicrete and or some calsil board.
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Old 02-10-2014, 01:56 AM
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Default Re: Thickness of vermiculite concrete

Quote:
Originally Posted by david s View Post
Sisalation sitting against a conductive material like concrete renders it pretty much useless. It has to have plenty of air around it to work. embedding a layer in the vermicrete slab would be better, but it will then act as a vapour barrier and make drying the vermicrete really difficult. i'm with the others either more vermicrete and or some calsil board.
thanks for that david...was more of a crazy idea as i have a heap of it lying around. won't bother. will just fork out for the board i reckon.

although, anothe question. Ive had one guy at a refractory tell me that his calcium silicate board would need to be 50mm (2 inches), where as another refractory that makes ceramic fiber board says 25mm (1 inch) will be suffice and is the equivalent of the 50mm in calsil...

thoughts?
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Old 02-10-2014, 02:10 AM
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Default Re: Thickness of vermiculite concrete

G'day
The question I ask is not really why you need that level of insulation under the hearth.
It's really Why is is 4 ins of pearlcrete such a problem?
Regards dave
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Old 02-10-2014, 02:12 AM
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Default Re: Thickness of vermiculite concrete

Because i have made an error with the height of the wall already, so adding 4 inches of vermiculite concrete, and then the hearth will make it too high....hence I am hoping to get the same effect with 25mm of board...i know its only 50/75mm difference but its enough to make it visually too high...imho...

so if 25mm ceramic fibre board will do the same as 50mm calsil board then sweet...
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Old 02-10-2014, 02:18 AM
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Default Re: Thickness of vermiculite concrete

just noticed i keep switching from metric to imperial inches to mm...
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