Here is how I built my metalmelting foundry. It is composed of:

150 kg of concrete
60 kg of mortar
25 kg of refractory cement
56 bricks
1 steel adapter

The lid will be composed of:

30 kg of concrete
5 kg of refractory cement
60 cm of Rebar
1600 cm² of expanded steel lath

In hindsight, I recommend beginning to cure your refractory cement immediately after applying it. First by using lots of forced air, and then slowly heating it up to it's curing temperature. Then slowly cooling it down again.

Thank you for watching. =)