How to Make a small Gas Furnace

Step 4 Some Quick Notes

For those people who can't get XL refractory clay, there are others, more available and less available. The cheapest one i can think of is Adobe. This is simply a 50-50 mix of sand and clay. (no pebbles or rocks) Mix the sand and clay and apply them immediately, then let them dry completely before firing the adobe. After it's been fired once, it's ready for use.
Anyone living near a ceramic supply house or brickyard should be able to find something that'll do the job.