Vermiculite - How much?

[Robarb]

Typically,for a castable oven with an internal diameter of 50-60mm, how many 100kg bags of vermiculite would i need for:

An insulation layer 50mm, or 100mm thick
A solid base 1.1m x 1m and 100mm thick?

I don't know how far the stuff goes when mixed with cement for a vermicrete mix.

Is it a 5:1 ratio for both elements?

Thanks

[david s]

As 50-60mm is only 2-2.5" in diameter then your oven is really tiny and would require about half a litre of vermiculite to insulate it. If however you presumably meant 500-600mm and assuming you are only insulating with vermicrete (no blanket) then you'll need almost two 100 litre bags for a 4" thick insulation layer. When you mix cement and water with it there will be around 20% reduction in volume because it compacts a bit, as well as a fair amount of stuff spilt when applying it to the oven. You can easily calculate the required volume using the formula for the volume of a sphere (4/3 pi r3) but don't forget to halve it because it's a hemisphere.

[Robarb]

Thanks David.

Yes i did mean 500-600mm but, i probably meant 700mm, that's what you get for using a keyboard on a phone! ... anyway i was essentially weighing up the costs of going all vermicrete vs ceramic blanket for the insulation, but, by the time you've bought all the cement and the additional weight and size the 4" vermicrete adds, it'd be cheaper to buy the blanket.

Is there any particular ceramic blankets that are better than others? I think i read superwool was a good one.

Regards

[david s]

I use super wool. It’s great insulation, beautiful to cut and fit. Because it’s dry there’s no need to dry it before working over it. Making your own vermicrete layer is cheaper but more labour intensive. Generally a layer or two of 25 mm thick blanket, topped with a layer around 35mm 10:1 vermicrete provides a good solution.

[Robarb]

david s thanks.

So with a bit of wire over the blanket holding it in place, you can put a 35mm vermicrete mix straight on top?

What is the ratio for the vermicrete insulation sub base under the CaSi board, i thought that was 10:1?

I presume you can then finish this with a final water proof render layer?

Kind Regards

[UtahBeehiver]

5 to 1 under floor is required for strength. 8-10 to 1 on dome insulation