How to Repair Damaged Plaster Walls

Repairing Damaged Plaster Walls

How to Repair Damaged Plaster Walls Whatever you intend to use as a decorative finish, plastered walls or ceilings must be made good by filling cracks and holes.

Patching plasterwork can be a messy job and if you are not careful you can end up with white footprints all round the house. Cover the floor around the work area with dust sheets, particularly if you are unable to remove the carpets. If you are working overhead also cover the furniture.

You don’t need to be an expert plasterer unless you are faced with repairing large areas of loose plaster, in which case it is worth hiring a professional.

There are easy-to-use fine fillers available, but if you need to make good a thick coating you can use the traditional undercoat and top-coat plasters or one of the newer one-coat plasters. Let plaster and fillers dry out thoroughly before you begin to apply paint or wall-coverings.

Essential tools:

  • Bolster chisel
  • Filling knife
  • Hammer
  • Paintbrush
  • Plasterer’s trowel
  • Tinsnips
  • Wallpaper scraper


Levelling the repair

Uneven plaster can spoil any decorative finish. Use a straight-edged batten to help level the surface of a plaster patch before finishing with a trowel.

Filling Cracks and Holes

Special flexible emulsions and textured paints are designed to cover hairline cracks, but larger ones will reappear in a relatively short time if they are not filled adequately

  1. Rake loose material from a crack with the blade of a scraper or filling knife. Undercut the edges of larger cracks in order to provide a key for the filling. Mix up interior-grade cellulose filler to a stiff consistency or use a premixed filler.
  2. Dampen the crack with a paintbrush, then press the filler in with a filling knife. Drag the blade across the crack to force the filler in, then draw it along the crack to smooth the filler.. Leave the filler standing slightly proud of the surface, ready for sanding flush with abrasive paper. Fill shallow cracks in one go; but build up the filler in stages in deep cracks, letting each application set before adding more.
  3. Fill and rub down small holes and dents n solid plasterwork, using the methods recommended for filling cracks.


Gaps between skirting boards

Large gaps can open up between your skirting boards and the wall plaster. Cellulose filler simply falls into the cavity behind, so bridge the gap with a roll of press-in-place butyl sealant.

Patching Up Damaged Corners

Cracks sometimes appear in the corner between walls or between the wall and ceiling; fill these by running your finger dipped in filler along the crack. When the filler has hardened, rub it down with medium-grade abrasive paper.

  1. To build up a chipped external corner, dampen the plaster and use a filling knife to scrape the filler onto the damaged edge, working from both sides of the corner.
  2. Let the filler stiffen, then shape it with a wet finger until it closely resembles the original profile. When the filler is dry, smooth it with abrasive paper.

Patching a Lath-and-Plaster Wall

If you live in an older house, you might find that a wall between two rooms is hollow. This type of partition wall is made with a timber framework covered with thin strips of wood known as laths which serve as a base for the plaster. If the laths are intact, just fill any holes in the plaster with cellulose filler or fresh plaster. If some laths are broken, you need to reinforce the repair with a piece of fine expanded-metal mesh.

  1. Rake out loose plaster and undercut the edge of the hole with a bolster chisel. Use tinsnips to cut the metal mesh to the shape of the hole, but a little larger.
  2. The mesh is flexible, so you can easily bend it in order to tuck the edge behind the sound plaster all round.
  3. Flatten the mesh against the laths with light taps from a hammer and, if possible, staple the mesh to a wall stud to hold it.
  4. Apply one thin coat of backing plaster and let it dry for about an hour before you fill the hole flush with more plaster.

Filling Holes in Plasterboard Walls

Use plasterer’s glass-fibre patching tape when mending holes up to about 75mm (3in) across.

  1. Stick on the self-adhesive strips in a star shape over the hole, then apply cellulose filler and feather the edges.
  2. Alternatively, use an offcut of plasterboard just larger than the hole yet narrow enough to slot through. Bore a hole in the middle and thread a length of string through. Tie a galvanized nail to one end of the string.
  3. Butter the ends of the offcut with filler, then feed it into the hole. Pull on the string to force it against the back of the cladding, then press filler into the hole so that it is not quite flush with the surface. When the filler is hard, cut off the string and apply a thin coat of filler for a flush finish.

Patching Larger Holes in Plasterboard Walls

A large hole punched through a plasterboard wall or ceiling cannot be patched with wet plaster only.

  1. Using a sharp craft knife and a straightedge, cut hack the damaged board to the nearest studs or joists at each side of the hole. Cut a new panel of plasterboard to fit snugly within the hole and nail it to the joists or studs using galvanized plasterboard nails.
  2. Use a steel plasterer’s trowel to spread finish plaster over the panel, forcing it well into the edges. Allow the plaster to stiffen, then smooth it with a dry trowel. You may have to add another layer to bring the patch to the level of the wall or ceiling.

08. December 2010 by admin
Categories: Construction, Decorating, Restoration and repairs | Tags: | Comments Off on How to Repair Damaged Plaster Walls


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