Bought an old sandstone rock house built in the late '20's. Over the years its been added on to, walls covered, roof structure compromised, etc. Oddest structure I've ever come across. 

Walls are stacked sandstone mortared together. Inside a board runs at the top of the wall and another at the bottom horizontally. Connecting the two are 12" wide boards running from floor to ceiling. The roof joists tie to the top board, the floor joists tie to the bottom board. No cavity or insulation.

At some point the walls were covered with cardboard boxes and newspapers ... then wall paper ( multiple layers ) ... then drywall ... then paneling (Ooh-la-la). The newspapers have been a fascinating read from 1938 to 1956, but that's another story.

Our problem is that part of one wall is leaning outward. The rest of the walls don't have a crack anywhere not even over windows or doors. There is a window in the middle of the part that's leaning that we planned to repurpose as a doorway leading into an addition. But I need to fix the wall and I have zero experience in working with sandstone masonry walls.

Our options, as I see it, are to 1) buttress the wall and leave the lean knowing it won't further lean, 2) build the new room using the structure of it to buttress the rock walls on either end of the lean and remove the leaning portion, 3) possibly use an earthen/cob plaster technique to stabilize the wall, 4) ????

We are in the country so we aren't constrained by any city or county codes other than elevation of floor level for flood plain. Our design essentially builds a new structure surrounding the existing structure so no new loads will be placed on the stone walls. 

Anyone with experience willing to chime in?