Newcomer needs advice

[Dave Blakey]

Hi to anybody who can help me.
I had the crazy idea of building an oven in garden in north east England.
We are now at stage of putting an insulation layer between concrete bed and the oven floor. Going to use a vermiculite mix. What is mix ratio and with what is best to mix it with. What is best depth od layer? Sorry for all questions but I do need the advice. Thanks

Dave