My first furnace

Click on any image to see a full size picture.

... so that the top part is the width of the form & the bottom part is just long enough to make the surface of the top part level with where you want the floor of your furnace.

You will need

Building sand
Perlite
Fireclay
Portland cement (not shown)

I have used 4 litres of Perlite to 2 litres of sand, 2 litres of fireclay & 2 litres of cement.

I mixed it with water applied with a sprinkler until I could created a ball of mixture which would not fall apart on its own.

Fill the bottom of the tank by hand & tamp the mixture around the wooden form.

Insert the main form & ram the mixture around the form using a suitable piece of wood.

Sadly, I made far too little mixture & I only managed to fill the tank less than half way. It was getting late & I had to call it quits for the night.