I've been baking SD over the last year, getting much of my info from
this newsgroup. One chronic problem I've had is soft crust. Right out
of the oven, the crust is really hard (so hard I have trouble sticking
a thermometer in it), but within an hour it becomes spongy enough to
press in with your fingers. The bread is otherwise fine and tasty, but
I prefer hard crusts.

Here is some background info about my technique:
-dough is made of bread flour, starter, salt, and water
-preheat to 500 in electric oven w/ pizza stone for 45 min
-pour boiling water into pan near bottom of oven right before putting
bread in
-slash 1kg loaf, spray lightly w/ water, slide onto stone with peel
-after 10 min, turn temp down to 400
-bake ~35 min more
-check temp inside bread (usually between 200-215)
-cool on wire rack at room temp for at least 2 hrs

The crust becomes progressively softer starting after about an hour of
cooling, with the bottom of the loaf degenerating first. I've varied my
technique in a number of ways (with no success) including:
-trying different cooking temps from 400 to 525, often lowering it 10
min into baking, but not always
-making less steam by not spraying loaf w/ water and not putting a pan
of water in oven
-making more steam by spraying water in the oven every few minutes in
addition to the pan of water
-shaping loaf in a banneton and shaping it as a freeform loaf
-varying rising times from 2.5 hrs to 7.5 hrs
-autolysing and not autolysing the dough at the beginning

I consulted a cookbook from "America's Test Kitchen" that said soft
crusts were caused by too-high temps and recommended baking at 500
initially and then lowering it to 400. Didn't work.
I don't know what possibly could be causing me problems; I've run out
of ideas. But if anybody has had similar problems and figured out a
remedy, please let me know.