You may think the hardest part is over when you remove wallpaper from plaster walls, only to discover you need to tackle the adhesive. Wallpaper glue bonds quickly and effectively to plaster walls, so removing it requires loosening the adhesive enough to wipe it from the wall without harming the surface. Remove wallpaper glue from a plaster wall the same as you would drywall, with a combination of soap and water and physical effort.
Fill a large spray bottle with warm water. Pour 2 tsp of mild liquid dish soap into the bottle. Replace the lid and shake the bottle to distribute the soap.
Lay towels or sheets on the floor under the plaster walls to catch any water runoff.
Spray the wallpaper adhesive with the soapy water. Allow the liquid to loosen the glue for 10 to 15 minutes.
Fill a bucket with warm water. Wet a cloth with the water. Starting at the top of the plaster wall, begin wiping the adhesive from the surface. Dunk the cloth into the bucket of water to remove the adhesive as you continue wiping down the wall.
Respray areas of hard-to-remove adhesive with additional soapy water and allow it to remain on the walls for another 10 minutes. Rinse the adhesive and all the soap from the walls with the wet cloth. Dry the walls with clean cloths.