How to skim plaster walls

Written by robert sylvus
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How to skim plaster walls
A skim coat gives plaster walls a smooth and flat surface. ( Images)

A skim coat added to a plaster wall removes the bumps and depressions in an old plaster wall's texture or hides a new plaster wall's imperfections. The smooth, flat surface of skimmed plaster readily accepts wallpaper or new texture. The base coat a plaster installer applies to a wire-lathe-covered wall consists of at least 2 layers of a gypsum-based plaster. Once the base coat dries, the installer works a skim coat into the plaster wall's base coat. Remodelling contractors usually do not remove an old plaster wall's texture before applying the skim coat.

Skill level:

Things you need

  • Sponge
  • Water
  • All-purpose joint compound
  • Lime
  • Electric drill
  • Cage bit
  • 5-gallon bucket
  • 12-inch flat trowel
  • 24-inch flat trowel
  • Sanding block
  • Light

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  1. 1

    Dampen a sponge in water and clean the plaster walls.

  2. 2

    Mix a bucket of all-purpose joint compound with an electric drill equipped with a cage bit until the joint compound's consistency matches warm butter. Premixed joint compound comes from the manufacturer in a bucket with all the ingredients included. Professional plaster installers commonly mix the plaster manufacturer's recommended ratio of fast-set powdered joint compound, lime and water in a 5-gallon bucket.

  3. 3

    Skim a coat of the joint compound 1/16 inch thick onto the plaster wall with a 12-inch flat trowel. Start at the top of the wall and feather the skim coat toward the floor. Cover the entire wall.

  4. 4

    Hold a 24-inch flat trowel at a 45-degree angle and use the edge of the trowel to smooth the skim coat. Start at the top of the wall in 1 corner and work toward the floor. If the skim coat starts to stick to the trowel's blade, wet the blade with water.

  5. 5

    Let the skim coat dry completely, using the joint-compound manufacturer's dry-time guide. Premixed all-purpose joint compound takes 24 hours to dry. Fast-set joint compound states the dry time on its bag, usually between 5 and 30 minutes.

  6. 6

    Set a light on the floor next to 1 corner of the plaster wall. Shine the light across the wall's surface. The skim coat's imperfections and ridges will show up as shadows.

  7. 7

    Dampen a sanding block in water.

  8. 8

    Remove the ridges and imperfections in the plaster wall's skim coat with the damp sanding block, using the shadows from the light as a guide.

  9. 9

    Apply a second skim coat if the first skim coat did not hide all of the plaster wall's imperfections or texture.

Tips and warnings

  • Work on 1 wall at a time.
  • Amateurs should avoid using fast-set plaster with lime due to its quick-setting nature.

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