Hyperboy, I don't have an answer for you but I didn't want you to think you were being ignored :-)

The jury's still out on how long hypertufa will hold up. It's also a less durable mix and I'm not sure it would hold up to the kind of foot traffic that stairs require. If I were doing this project, I'd make the steps out of readymix to get the strength of that gravel aggregate. If I REALLY wanted that hypertufa "old stone" look, I'd apply a coating of it to the stairs.

Hope this helps--please let us know how your project goes.

Deb

Deb,
Thanks for your reply. I think I'm in the process of talking myself out of hypertufa slabs and am now moving more toward the concrete route you suggested.
It's occurred to me that I can(hopefully)dig a slab-shaped depression right into a flat area of ground near my shed, pack and sculpt the sides to give it an irregular stone slab look, then simply pour a concrete mixture directly into this cavity. I might even toss in a length or two of rebar. Once this slab sets up, I SHOULD be able to dig it up and dress the surface with a stiff brush and a hose.
I did a small (cobblestone-sized) test batch last night. The recipe I used was one part cement, two parts coarse sand, one part washed brownish pebbles (about jellybean-sized) and one part georgia clay. The mixture was brown and... interesting. I'll dig it up this evening, gently scrub and hose it, and see what I have.