I grind my own flour and regularly make whole wheat breads at about 85-90% hydration to get an open crumb - not as open as with white flour, of course, but holey enough for me.
Anyway, I bought 6 pounds of spelt berries a couple of weeks ago and started up a spelt sourdough starter. I made a round loaf of 50-50 whole wheat / whole spelt at 85% hydration. Lovely crumb, lovely flavor. Big ole pancake of a loaf. It spread out something awful in the oven.
I've previously made a sourdough sandwich loaf with 50-50 whole wheat - whole spelt at 80% hydration, and it turned out great. A bit less of a rise than 100% wheat, but still acceptable, and the flavor was really nice. Tangy and nutty. But the loaf also had butter, milk and some honey in it, which could have made a difference, I suppose. The round was just flour, water, salt and starter.
I developed both the round and the sandwich loaf using the stretch and fold method described by Mike Avery (i.e., mix until all is hydrated, rest for an hour, then fold ever 45 minutes or so). I folded three times.
I see several possibilities for why the loaf spread:
1) I've read that spelt doesn't absorb as much water as wheat. Perhaps I added too much water?
2) I've also read that spelt's gluten is more fragile than wheat. But, as I said, the pan loaf rose just fine.
3) Perhaps I didn't develop the dough well enough? (again, though, the pan loaf was fine)
4) Maybe my shaping needs help. I was trying to be as gentle as possible, so maybe I was a bit too gentle.
Anyway, if anyone has any experience working with whole spelt and has tips and pointers, I'd be most appreciative.