Possible to salvage bowed sandstone slabs for porch steps?
"Itacolumite is a naturally occurring porous, yellow sandstone that is flexible when cut into thin strips." –Wiki

"Most of the known flexible rocks are also fine-grained; in some cases they are said to lose their flexibility after being dried for some time, probably because of the hardening of some interstitial substance, but many specimens kept in a dry atmosphere for years retain this property in a high degree." Can A Rock Bend? –geocaching.com



I think you're on to something with getting it wet, but I've no idea how long it might take to straighten; probably long enough that you'd need new stairs in the interim anyway.

Shore them up as best as possible and use a 20 amp grinder with a diamond wheel to flatten them? Sounds like a lot of work... but sandstone is awfully soft.

Really though, if they're all off by exactly the same amount, then danger is minimal IMO. Grinding them down will ruin their patina, so from an esthetic view point, I'd leave them alone after shoring them. That's assuming that walking up and down them doesn't feel funny, and that they're all true to each other heightwise within 3/8 of an inch at any given point.

I'd prefer you put your efforts into installing railings. Hopefully that's part of your rebuild plan. If you have to move them make sure you have help and that you both choke-up on it so that they don't crack in half under their own weight when you pick them up.