How much vermiculite will I need to buy?

[boccu]

I am building a 36" oven and have poured the first layer of concrete for the base and now need to put in the insulation layer prior to the actual cooking floor. I have found a calcium silicate board that I could purchase (in NZ) but the cost of putting in 2 layers of 9mm board will exceed $200. My other option is preparing vermiculite concrete at a cost of $76 per 100 ltr bag ...... has anyone kept record of how much vermiculite will be needed for this part of the build?

[david s]

I am building a 36" oven and have poured the first layer of concrete for the base and now need to put in the insulation layer prior to the actual cooking floor. I have found a calcium silicate board that I could purchase (in NZ) but the cost of putting in 2 layers of 9mm board will exceed $200. My other option is preparing vermiculite concrete at a cost of $76 per 100 ltr bag ...... has anyone kept record of how much vermiculite will be needed for this part of the build?

The short answer is, more than you think. The volume is decreased by around 20% of the dry volume of vermiculite because it compacts somewhat when wet and mixed. $76/100 L is expensive. Because you live on a volcanic island you might have access to pumice which is an alternative aggregate to vermiculite or perlite and could/should be way cheaper or even free if you know where to look. You may have to crush it down so there are no grains bigger than 6 mm