I have a couple of sheets of spare plasterboard and used it to replace the plywood on the ceiling in my downstairs bathroom. I'm looking to renovate and wanted to use either XPS or Marmox boards on the walls, skim the ceiling and halfway down the walls to a dado rail for wallpaper. I'd quite like to not have to rip this plasterboard down from the ceiling. Can I joint between plasterboards and XPS/Marmox Multiboards or is it one or the other?
