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Severe impact damage can dislodge areas of plaster from the masonry behind, leaving a hole too big for filler to cope with. Plaster can also separate from its backing due to old age, often aided by the effects of damp or condensation. The ideal product to use to repair this kind of damage is Wickes Patching Plaster.
Start by tapping the plaster round the damaged area to see if any more sounds hollow. If it does, hack it off with a bolster chisel and hammer until you have a sound edge. Undercut it, then brush out all dust and loose debris.
Mix up a quantity of patching plaster in a bucket, to the consistency of thick porridge. Then transfer some to a hawk - a small square board with a handle fixed to its underside.
Use a garden spray gun or an old paintbrush to wet the wall and prevent suction from drying out the new plaster too quickly. Then take some plaster off your hawk with a metal plasterer's trowel and press it hard into the base of the hole. Take up more plaster as necessary, aiming to fill the hole to within about 3mm of the surface, and leave to harden.
Mix up a little more plaster to a runnier consistency and trowel it on to fill the hole flush with the surrounding plaster. Polish the surface with the trowel, spraying on a little more water if necessary to give it a smooth hard finish. Leave it to harden, then sand it with fine glasspaper if necessary to remove any nibs of plaster from the wall surface.
Cracks at the wall-ceiling angle and along the join between skirtings or architraves and the walls are caused by slight movement in the house structure as temperature and humidity levels change. This movement makes hard fillers crack and fall out.
The solution is to use a non-setting mastic sealant to fill these cracks. Rake and brush out any loose material from the crack, then apply a neat bead of Wickes Decorators' Filler using a cartridge gun. Smooth off the bead with a moistened finger and leave it to skin over. You can then paint or paper over it, confident that the crack will not open up again and spoil your decorations.
Plasterboard is an excellent material for surfacing ceilings and timber-framed internal partition walls, but it is relatively brittle and impacts will leave a hole in the board. How you go about repairing it depends on how extensive the damage is.
For small holes - caused for example by bashing the wall with the corner of a piece of furniture when moving it - you can stick a piece of plasterboard joint tape over the repair to patch it. Use glasspaper to feather the hard edges of the tape and then skim on a very thin coat of plaster to conceal it.
If the hole is more than about 25mm across, you need a more substantial repair. Neaten the jagged edges of the hole with a sharp knife. Then cut a scrap of hardboard to a rectangular shape, longer than the hole width in one direction and a fraction narrower in the other. Make a hole in the centre, pass some string through it and knot one end.
Spread some PVA woodworking adhesive on the ends of the strip, feed it into the hole and use the string to pull it back against the inner face of the board. The adhesive will hold it in place after a few seconds of firm pressure. Leave it to set, then cut off the string.
Fill the backed hole with filler, as if you were repairing a hole in solid plaster, and sand it flush with the surrounding plasterboard.
If the board is seriously damaged - for example, by a foot slipping off a loft joist and breaking through the ceiling - you will have to patch the damage. Use a pencil and straightedge to draw two lines on the ceiling at right angles to the joist direction so they enclose the hole. Then use a padsaw to cut the plasterboard along the marked lines until you reach the adjacent joists. Mark their centre lines and use a knife to cut through the board along these lines. Pull down the severed sections of board to leave a neat rectangular hole in the ceiling.
Cut a piece of new plasterboard to fit the hole and secure it to the joists at each side with plasterboard nails. Then bed lengths of plasterboard tape over the joins using runny patching plaster as the adhesive, and skim a thin layer of plaster over the whole patch to conceal it.
Patching large holes in plaster
Use a straightedge to level plaster in a patch larger than your trowel, working it from side to side.
Patching small holes in plasterboard
Stick a hardboard offcut to the inner face of the board with PVA adhesive to support the filler.
Patching large holes in plasterboard
Cut away the damaged board to leave a rectangular hole, and nail in a patch of new plasterboard.