so, I have a post-frame shed, 12x16. there are posts at 6' on the short sides and every 4' on the long side. posts are set ~18" below grade, on a 2" cap of cement over a few inches of well compacted gravel, holes were all about 27" or so, 2x6 girder runs level at the top (very level all the way around) around base, ok, so, basically I have ~5.5" to grade from bottom of 2x6 girder to top of board, and the Ive got posts set in concrete, at 24" from the top of that board so I want to fill that in with concrete, I could put gravel in, say 2" and 3.5" of concrete over that.
Its about 3.75 cu yards of crete, or like $400 It will cost $100 for gravel to fill in 2", but my crete is still only a little cheaper, and it will be a thinner slab.
I could put gravel in, say 2" and 3.5" of concrete over that or just full 5.5" of crete or I could do lot of gravel and a 2" top coat over that with a bunch of steel and fibers,
Its just a shed, so Im not too worried about it, I'll put steel mesh in and probably fiberglass to control cracks and run a groover down the center.
Point is, can I get away without using gravel and just lay plastic down and pour a slab, or is the clay soil going to destroy it if I dont have a couple inches of gravel. I am not, going to dig this down deeper, or pour higher that the girder.
Its 5.5" of space, with a few low spots I can rake out. It much faster to do a one day pour so I can put my books back in and my tools to keep them dry, so full 5.5" concrete is good and fast, but a couple inches of gravel would be nice, but is a total extra set of work for little gain
thoughts? (yes, I should have done this in a different order, it was not an option at the time)