How to Repair Plaster Walls for Wallpaper Preparation

Written by laura reynolds
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One of the joys of owning an old house is in learning about the craftsmanship that went into making a home before prefabs and sheet rock. Although wall board has been used since the early twentieth century, most homes built before mid-century had plaster walls--and those that were built using wallboard had plaster over the wallboard. Hanging wallpaper over old (or new) plaster walls is easy if you do some minor repair work before sizing the walls.

Skill level:
Moderately Easy

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Things you need

  • Can opener
  • Sandpaper
  • Spackle
  • Patching plaster
  • Plaster tape
  • Assorted putty knives
  • Stiff brush
  • Spray bottle with water

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Instructions

  1. 1

    Inspect the walls carefully before starting. Imperfections that are almost invisible on a painted wall will show up immediately under wallpaper. Find patch edges, pin or nail holes and uneven areas that may or may not be the result of past repairs. Find any cracks, no matter how small. Mark these areas with a soft lead pencil as you work your way around the room. Inspect the area again, going the opposite way so you can see the surfaces from a different angle.

  2. 2

    Wash the entire area well to remove any grease or grime that's settled from household air and cleaners. Use a painter's soap, like trisodium phosphate or any other soap recommended for cleaning walls prior to decorating. Remove any coating, like the wax used on Venetian plaster, that might prevent wall size or paper from adhering. Spackle nail holes and hairline cracks before taking on larger projects. While the spackle is drying, sand any ridges or patch edges flat. Sand spackle edges. If the wall has been painted with a high gloss or oil-based paint, you can sand a bit to rough up the surface.

  3. 3

    Fix the cracks and smaller holes. Use putty knives, a stiff brush or the sharp end of an old-fashioned can opener to score and remove any loose plaster. Cut plaster out from under the edges to "key" or anchor the new plaster. Use plastering tape for cracks or small holes and cover with a thin coat of patching plaster. Use plaster anchors in any areas around patches that you think might loosen in the future. Countersink anchors and cover with patching plaster or spackle.

  4. 4

    Repair larger cracks and holes by repairing and applying a new mud-, or base-coat of plaster. Mend missing wallboard or lathes by preparing a piece of wallboard or crumpled chicken wire a bit larger than the hole or crack behind the wall. Loop a few strings through it to hold on and slide your patch behind the wall. Hold on to the strings as you apply your mud coat, keying to the patch. Be sure to spray water on existing plaster before you start and as you work. This will help the new plaster adhere to the old, minimising the possibility of new cracks. After the mud coat dries, trim the strings and apply the finish coat of plaster. Be sure to spray the area with water before beginning the finish coat.

  5. 5

    Sand repairs with medium to fine grit sandpaper to be sure that the surface is flat and smooth. Fill any areas that are low--plaster shrinks as it dries--and sand when dry. Prime any new plaster before sizing the wall. The calcium and lime in plaster will spot through wallpaper.

Tips and warnings

  • Chicken wire makes an especially good base for patches because the mud coat can be driven down into the chicken wire to form keys that will hold the two sides together tightly. If you're going to use wall board, punch a few holes in it to form keys.
  • If you use a wide putty knife to scrape down edges, remember that a sheen can develop on plaster when it's scraped with a steel knife. Be sure to rough it up with some fine sandpaper before painting.
  • Be patient when patching plaster. Be sure to let base coats dry before adding finish coats. If you cover a base coat too soon, the finished patch will stay damp longer and will not form a good base for primer or wall sizing.

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