and used width and length of 7 feet which makes a total of 49 square feet, with the depth of 4 inches and it says thats 463 liters which sounds much more plausible.
Then we have the cement, I had a quick Google and a 25kg bag comes in a 33liters ish.
You then have to pick the ratio you wish to mix at, usual ratios are 1:6 or 1:8 as the cement will make part of the final volume but make sure you have spare as its not going to be as exact as vermiculite is slightly absorbent.
if using 1:8 then you need a third of a bag of cement for each bag of vermiculite, so a total volume if 111 per bag of vermiculite.
So I would expect 5 bags to be required to cover the whole base with 2 bags of cement.
I do not know if this changes ratio wise with fondu.
Also why fondu? is that not more expensive that regular cement? I do not see why you would use that?
you will need to run more specific numbers than the ones I have here prior to ordering but its good you checked as I think 2 bags as you suspects is off the mark slightly.
I used thermal breeze blocks as they were easier to calculate and quicker to fit, but casting this should be pretty easy work, just make sure you have something big and light you can mix it all in.
John, your calculation looks right for the dimensions that you give (as is Turkey's). I think I used just under 5 100l bags of vermiculite, roughly spilt equally between the floor and a 50mm vermicrete layer on the dome of a 42" id wfo (apols for mixed units).
fondu and vermiculite is sold by local refactory at good price for ireland.
if i do not need fondu and cement will do for the base then feck that i wont use fondu. wasnt aware that could use a vermiculte/cement combo for base. just the vermiculate 6:1 i saw said use fondu but thats easy say when trying sell it to me
I (actually...many of us) have used thermolite blocks as a thermal layer between hearth and slab. I only use vermiculite over the thermal blanket on the dome (vermecrete).....then for a 90cm internal diameter oven I find that 3 full bags is barely enough for a 3" layer.
thermalite is a brand but any similar product would be suitable, any builders merchants and even high street diy chains (we have wickes and b and q here) stock them, they are the bread and butter of building blocks for new houses as they are strong and insulate well.
they are probably referred to generally as aerated concrete blocks, or breeze blocks. ?
can be cut with a wood saw as well which makes them very easy to handle.