How to Take Off Wallpaper from Plaster with a Wallpaper Steamer
Once the wallpaper is removed, wash the walls with a solution of wallpaper removal solvent.
Wash off any remaining adhesive residue with wallpaper removal solvent or with a nonphosphate cleaner in water, using a large sponge or sponge mop.
You can use an abrasive pad or steel wool to help you remove the adhesive residue on plaster, but use caution on drywall. Avoid overwetting or abrading the cardboard facing that’s on the drywall.
Rinse your sponge often in a separate bucket of water, squeeze it out, and continue rinsing your walls until all the residue and remover solution are gone.