Secure a sagging lath and plaster ceiling

Support the sagging section, screw repair washers through the plaster into the joists, then fill and repaint for a lasting fix.

SLC-01Clear the room and check for asbestos riskMove furniture out or into the middle of the room and cover everything with dust sheets, including the floor. Wear an FFP3 dust mask and goggles — old lime plaster dust is unpleasant to breathe and gets in your eyes when you're working overhead. If the ceiling has a textured coating (like Artex) and the house was built or the ceiling done before 2000, stop and get a sample tested before you sand, drill or disturb it, as some textured coatings from that era contain asbestos.

RULES

2 each · Dust sheet

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1 pack · FFP3 dust masks (pack of 5)

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1 each · Safety goggles

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KNOW THE RULES

Some textured ceiling coatings applied before the mid-1980s to 1990s contain asbestos. The Control of Asbestos Regulations 2012 require you to identify and manage this before disturbing it — get it tested if you're not sure.

SLC-02Assess how bad the sag isPress very gently on the sagging patch with your fingertips — don't lean on it. A bit of give with a dull thud usually means the plaster keys have broken but the lath is still sound enough to fix. If it feels soft, crumbly, or you hear cracking and grinding as you press, or the sag covers a large area, this is beyond a simple repair and needs taking down and re-boarding instead. Check above the sag for brown staining too, as this can mean a leak caused the sag, not just old age.

1 each · Torch

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SLC-03Find and mark every joist under the sagging areaLath and plaster ceilings are always fixed to timber joists — there's no metal stud version, so you're only ever looking for wood. Use a stud/joist detector, or a strong magnet swept slowly to pick up the old nail heads, and trace each line of nails across the ceiling; the hollow sound changes to a dull knock over a joist. Mark a pencil line along each joist across the whole sagging patch so you know exactly where to fix later.

1 each · Stud/joist detector

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1 each · Pencil

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SLC-04Check for cables before you drillLighting cables very often run across ceiling voids, so sweep the whole sagging area with a cable and pipe detector before you drill anything. Treat the detector as a warning, not a guarantee — it can miss cables that are deep, run in metal conduit, or sit outside where you'd expect. If there's any doubt at all, switch off the relevant circuit at the consumer unit before drilling, and don't switch it back on until you've finished and checked nothing's damaged.

RULES

1 each · Cable and pipe detector

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KNOW THE RULES

This step is about drilling safety, not notifiable work itself. But if you do damage fixed wiring and need to repair it, that repair may fall under Part P of the Building Regulations in England and Wales.

SLC-05Prop the sagging section back into placePad a length of batten or a small board with an old towel or cloth, then use a stepladder or an adjustable ceiling prop to push it gently up against the sagging patch. Push just enough to close the gap and bring the ceiling back roughly level — don't force it, or you'll crack the plaster further. This is easiest as a two-person job: one person holds the prop steady while the other fixes.

1 each · Padding cloth or old towel

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1 day · Adjustable ceiling prop (optional hire)

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SLC-06Screw repair washers through the plaster into the joistsAt each point where a joist line crosses the sagging patch, drill a small pilot hole through the plaster and lath into the joist — timber dust from the hole confirms you've hit solid wood. Fit a lath and plaster repair washer (a shallow domed disc, usually around 65mm across) over the hole and drive a 40mm No.8 countersunk screw through the centre and into the joist, until the washer sits snug and pulls the plaster back up tight. Space washers roughly 150-200mm apart along each joist line across the whole sagging area, and don't overtighten — you're pulling the plaster back into place, not crushing it.

1 pack · Lath and plaster repair washers (pack of 20)

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1 box · 40mm No.8 countersunk wood screws (box)

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1 each · 3mm wood pilot drill bit

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SLC-07Remove the prop and fill the repairOnce every washer is fixed and the ceiling feels solid, carefully lower and remove the prop. Fill over each washer head and any cracks with a flexible filler using a filling knife, feathering the edges out so there's no visible ridge. Leave it to dry fully, then sand smooth with fine sandpaper.

1 tub · Flexible filler

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1 each · Filling knife

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1 pack · Fine sandpaper (pack)

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SLC-08Seal, paint and clean upOnce the filler is completely dry, apply a mist coat (ordinary emulsion diluted about 70/30 with water) over the repaired area to seal it, then leave it to dry. Paint the whole ceiling to match, rather than just the patch, so the repair doesn't show. Take down the dust sheets, vacuum up any plaster dust and debris, and bag up rubble for disposal.

1 litre · Mist coat emulsion (diluted)

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1 2.5L tub · Ceiling paint

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1 pack · Rubble sacks (pack)

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