Drywall installed over plaster
Over the years I have worked on many old southern homes, homes Sherman did not burn to the ground, and they all had plaster walls, some walls were level others wavy. In some instances I used 1/4 inch drywall and others 1/2 depending on what shape the walls were in. The contractors had gone in and put in new wiring and plumbing and when I came in we just sheetrocked over the existing walls. I have done several renovations in Atlanta where all the homes were plaster, I put drywall on both ceiling and walls, and on one job I butted drywall to the plaster. If you are doing it yourself, use longer screws.