wish to add several bits to this topic. some of this may flie in the face of others respected ways and discoveries but this is not ment to detract or assert, just add to the accumulated information and encourage reading all the books, learn all we can from each other and then go fearlesly ahead with our own ideas as well.
In wisconsin i didn't wish to dig seven foot footers, we get frost to six feet in a year with no insulating snow cover, to get below frost line so built a "floating" concrete slab on a bed of drainage gravel topped with sand. The slab was sixteen inches in depth, of concrete and rock aggregate of various sizes reinforced with steel re-bar rods.
experience and hindsight said overkill to be sure, but we were learning by doing.
This was built in 1981. twelve years later, through some very cold winters the kiln and slab were still standing level.
the kiln sat on a course of concrete blocks and three layers of red constrcction brick, followed by two layers of apgreen#1's for the floor.
subsequently i moved to a heavy wet soil and again built a floating slab. this time four inches thick, on sand and reinforced as before.
bearing in mind the experience of a friend who didn't put enough insulating layers between the concrete and setting chamber with near tragic results, i again elevated the kiln on concrete blocks. this kiln and slab were still going strong when i moved again in 2000 to arizona.
my friend was walking away from stokeing his kiln,cone 8 was going down, when the moisture in the slab converted to steam and blew up . the kiln collapsed in on it's self after hurling a basketball size glowing pot past his head igniting the grass in a trail of fire as it landed and continued to roll.
one last thought, some years ago i had the privilege of fireing a coffin kiln built at uwlax. it was built on leveled earth. a heavy clay loam soil with springs underground. no footings, no drainage provisions, just three layers of hard brick on the ground and the walls up from there. we played for a year or so with this experimental kiln, had some fun, and some spectacular results.
sure it was a wet footed little beast, but the moisture was bringing up minerals from the soil with wonderful red flashing on raw clay. I couldn't get this effect with the same clay body in my kiln fourty milrs ayay i could go on about this, but i just wanted to illustrate it can be all about what one wants to achieve or to break with the common knowlge to find what else is possible.
thanks to all, who bring so varied much to this group.
Always peering over the edge, reverently takeing an irreverent look at everything.