Old 10-04-2013, 12:56 PM
Join Date: Oct 2013
Location: england
Posts: 5
Default Newbie Hearth Question

Lurked for a while and thought I ought to join.
Our oven project is coming on well. We are trying to keep costs down by using recycled products as much as possible. We are just about to lay the insulated hearth below the fire brick base.
The question is, to keep costs down, could we use broken glass as ballast mixed in with the vermiculite/cement mix? Would that work for insulation?
Thanks in anticipation.
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Old 11-20-2013, 11:48 PM
yorkshireknight's Avatar
Join Date: Feb 2013
Location: Veliko Tarnovo. Bulgaria
Posts: 114
Default Re: Newbie Hearth Question

Hi SB,

I remember seeing a video once of a guy using glass under his floor but I reckon he used it for heating purposes rather than insulation.
Not sure how it would work but the way I think about it is this.:

if you had a handful of glass and there was a fire on the top of it surely it wouldn't be long before you began to feel the heat, therefor that means to me that it would not be a good insulator to mix with the vermiculite.
I have heard of whole bottles being used as an insulator in pig stys for instance under the floor.
Your aim is to keep cost down but it is my understanding vermiculite is cheap.
Just my thoughts SB good luck.
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Old 11-21-2013, 02:57 AM
Master Builder
Join Date: May 2011
Location: South Australia
Posts: 621
Default Re: Newbie Hearth Question

Most insulators work by trapping air, a poor conductor of heat. Bits of glass won't do it. Vermiculite, or perlite, has air pockets in it.
Can you get scoria, or pumice? Lots of air bubbles trapped in the volcanic rock.
Off-cuts of Aerated Autoclaved Concrete (AAC) from a building site, maybe?
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