Our house was built in 1915. It has a number of cracks in the walls that run through several layers of paint and wallpaper. What can we do to eliminate them?
Whether you strip off the old wallpaper and paint or not, make a flat valley over the crack about 7.5 cm (3 in.) wide and 3 mm (1/8 in.) deep using a paint scraper. This will create the space necessary for strong plaster and fiberglass tape. Moisten the existing plaster and embed the tape in a layer of fresh plaster. Make sure that the tape is slightly recessed from the wall surface because it will be difficult to sand. Finish the job with a couple of coats of drywall joint compound for a smooth finish flush with the wall.