How much clay to build dome

[dickiejazz]

I am just completing my first oven. Base is all finished and well insulated.

Just waiting to start my dome now with a diameter of 28 inches. I want to put a 4 inch layer of clay down first follwed by ceramic blanket and 4 inche layer of wermicrret. Topped off with concrete screed. 

How much clay (preferably in Kgs please) will I need for the 4 inch  base layer.

Thanks in advance.

[downunderdave]

volume of a sphere is 4/3 pi x r x r x r. Calculate the volume of the outer volume using r 14+4 =28, then subtract the inner volume using r 14, then divide this by 2 because it's a hemisphere. Don't worry about the volume not required because of the oven mouth because you need around that much volume for its surround.