Scrape the paint bubbles or blisters with the putty knife. Remove all of the bubbles.
Peel any loose paint off the wall around the area of the bubbles.
Wipe the area with a damp cloth. This will remove dust or dirt. Allow 30 minutes to an hour for the wall to dry.
Apply a thick coat of primer with the paintbrush. Allow at least an hour for the primer to dry.
Sand the primer with the sandpaper until the wall is smooth. Wipe the dust off with a damp cloth.
Apply new paint to the wall with the roller.