I have an abandoned flue penetration in a 1920's stucco wall that I'm trying to patch. This is my first stucco adventure on the house, and I'm having trouble removing the stucco without shredding the paper. The penetration is on the weather side (comes at the wall from left to right) and probably leaked before (and obviously does now). It is ~3/4" stucco with chicken wire lath over 1x board sheathing, and I also happen to have the interior side open to the studs. The stucco is very hard and takes significant force to crack. The paper is very old, fragile and 'weathered'. The sheathing is in good condition so far.
I started smashing with a hand sledge and 1/2" cold chisel. Bashing a hole, then trying to cut parallel to the wall to avoid hitting into the paper. Online suggested smashing with just a hammer to break it down to the wire, but this didn't work either. Everything I've tried destroys the fragile old paper. I understand that water intrusion has rotted much of what I have exposed thus far, but even the areas that seemed to be getting better, I damaged the paper with delicate use of a small 1/4" chisel and a framing hammer.
The best method I have worked out is cutting a line with the chisel down to the wire, then starting perpendicular lines off of that, Making sure to break all pieces small enough before moving on (and leaving them loose, but wrapped around wire). Generally it is problematic large chunks that are loose, but firmly attached to the wire - any way you hit them, they puncture the paper... I also think it helps to leave the wire uncut longer for support.
To complicate things, there is a water table (visible top of photo), three PVC flues crossing the wall just above that, and a condensate line that I'll obviously have the remove. I was hoping the contain the repair to avoid removing additional plumbing, but I guess I'll see how far it goes...