When my condo was built, the upstairs sewer pipe was right up against the downstairs wall line. What the builder did was to remove the paper and plaster from part of the drywall, leaving the sewer pipe right against the exterior paper. When the upstairs toilet became misaligned because they didn't place it properly, the water ran over the edge of the pipe, down the pipe, and into the drywall. However, the downstairs wall was covered in heavy wallpaper, so the damage wasn't visible until we removed the paper years later. The drywall is all puckered around the pipe. When I removed the drywall, I discovered the close proximity of the pipe to the paper. I cannot move the pipe and I cannot move the wall. So I will have to remove some of the limestone on my patch to cover the hole in the wall and the pipe. Besides "very carefully," how do I remove the limestone without damaging the paper and losing wall integrity? Thanks.

 

A picture would certainly be helpful but it sounds like you'll just need to use spakling tape to cover over the pipe. How-to-insert-pictures.

 

Ideally you'd laminate the wall with another layer of drywall but that's easier said than done.
I'd get some of the wide mesh tape and put it down with a setting compound.
btw - drywall is made with gypsum not limestone

 

Not the first time that was ever done!

How much into the drywall?

If minimal you could cut back to the studs, add some furring strips to the inside and install 1/4" drywall across and finish.

If you need thinner, as mentioned you can cut away the bad and install mesh tape or even expanded metal (like they use for gutter covers) and just mud the entire area closed!

 

What are you doing with the wall after you patch it?

If you are planning on painting it then adding a layer of drywall is the way to go.