want to remove painted textured ceilings. They are a plaster base finish and have been painted several times. I here this can be quite the job.
Would it be best to simply remove old dry wall and replace or add another sheet of dry wall over existing dry wall.
It would be much easier to put another layer of sheetrock over the existing ceiling. Using longer screws, 1 5/8" or longer depending on what exactly you are going over. I have done this many times. Removing the existing ceiling will be quite messy. Still be sure to go perpendicular to the framing members. And if you don't use ceiling sheetrock, then you will want to use 1/2" on 16" centers and 5/8 on 24" centers. Also remember that you are going to be covering the ceiling so you can put holes in the old ceiling if necessary to find the framing members or for relocating lights.