On 02/02/2020 12:27, Dave Plowman (News) wrote:
https://imgur.com/e7pfZ2p
Put a bit of ply behind the joint and screw with plasterboard screws. Fill
the heads and join with decorator's caulk - you'll likely need a few goes
to get it perfect as it shrinks slightly.

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Although not obvious in the image, below the green line is ply for
around 6 inches so can secure with screws along that `green` joint.