Dirt Cheap Refractory

Being short on cash and time I decided not to buy some industrial refractory and decided to try my hand at making my own. This refractory is completely free as long as you have a shovel and a wheelbarrow. It contains only clay and sand. I dug the clay out of the ground myself from the unused land behind my house and the sand is out of a sand pit. I am still working on the formula but it does harden like rock when it is baked. I have not tested this in a furnace yet but once our first generation furnace is designed I will be lining the inside with this. I will post it holds up to heat/expansion stress.