How to fix old plaster walls

Written by tracy morris
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How to fix old plaster walls
Plaster walls may be patched easily. (Jupiterimages/Photos.com/Getty Images)

If your house is filled with cracked, crumbled or old plaster, it may be tempting to rip it all away and cover the wall with sheetrock. But there are many advantages to plaster that may make it worth an attempt to repair. Plaster is both durable and smooth. It provides strong acoustical deadining that can make it an asset in a city where ambient noise can be quite loud. Although plaster can crumble under stress, old, crumbled plaster is actually quite simple to patch.

Skill level:
Moderately Easy

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Things you need

  • Hydrated dolomite lime
  • 5-gallon bucket
  • Stirring rod
  • Mixing board
  • Trowel
  • Builder's sand
  • Dust sheet
  • Drill
  • Phillips head bit
  • Drywall screws
  • Plaster washers
  • Chisel
  • Mallet
  • Hand broom
  • Rough-textured drywall screen
  • Paintbrush
  • Bonding agent
  • Fibreglass mesh tape
  • Sponge

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Instructions

    Mixing Putty

  1. 1

    Fill a 5-gallon bucket 1/3 of the way with water.

  2. 2

    Add lime and stir until the mixture is the consistency of yoghurt.

  3. 3

    Cover the mixture with a 1-inch layer of water so that the mixture does not carbonate. Leave the mixture to sit. This process is known as slaking. The longer the mixture sits, the more the mixture improves. The mixture should slake for at least 20 minutes. You can prepare your plaster wall while the mixture slakes.

  4. 4

    Arrange a portion of putty in a circle around a mixing board. Place builder's sand that is not too coarse in the centre of the ring. Use one part putty to three parts sand. Mix the sand and putty until it is the consistency of dough.

    Repairing the Wall

  1. 1

    Place a dust sheet beneath the area where you will be working to catch falling plaster dust.

  2. 2

    Press firm plaster back against the lath backing. Slip a drywall screw into a plaster washer. Screw the drywall screw through the plaster and into the lath to reattach it.

  3. 3

    Chisel away any soft, crumbly plaster back to the lath. Remove the crumbling plaster back to the firm plaster. Chisel out plaster from between the slots of the lath. Brush the lath with a hand broom to remove loose plaster dust.

  4. 4

    Brush around the edges of the plaster surrounding the hole with rough drywall screen to roughen the surface and prepare it for fresh plaster.

  5. 5

    Brush the edges of the plaster, the lath and the plaster cracks with a bonding agent. You can purchase specially prepared bonding agents from a hardware store. Cover the lath, plaster cracks and any plaster being re-coated with fibreglass mesh tape.

  6. 6

    Press the first coat of putty firmly into the patch and around the edges of the holes using a trowel. The putty will ooze between the slats of the lath before hardening in place. Leave a slight indentation in the holes for the final application of putty.

  7. 7

    Press fibreglass mesh tape into the plaster to reinforce it. Allow the first coat of plaster to set.

  8. 8

    Apply plaster that is not mixed with sand over the holes and cracks in the plaster. Fill in screw holes with plaster to hide the screw heads. This process is called skimming. Use a sponge to smooth over surface imperfections.

Tips and warnings

  • You will not need to sand plaster that is patched using this method.

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