Pour 1 cup of white vinegar into a small bowl, and submerge the sponge into the vinegar.
Squeeze out excess vinegar. Gently rub the wallpaper adhesive in a circular motion with the sponge.
Rewet the sponge, and squeeze it to drain the sponge. Continue rubbing the untreated surface with the vinegar-soaked sponge, until the adhesive is soft to the touch.
Scrape the adhesive off of the untreated surface with the plastic scraper in an upward motion. Do not scrape up and down, as this can create scratches in the surface.
Rinse a cleaning cloth with warm water, and wipe the adhesive off of the surface. Wipe the surface with a dry cloth.