Bowing plaster ceiling

Hi,

First time poster so firstly hi.

In my my dining room (house was built in 1930's) I've noticed a long crack that runs along the sides of what must be the plasterboard, at closer inspection I've also noticed it appears to be bowing.

I've attached 2 photos so advice on what could be causing it and how to repair it would be greatly appreciated.

A 1930's build, more than likely lath and plaster than plasterboard, I would think. No matter, in either case the resolution may be the same.

First off is to find out if the joists supporting the ceiling are bowing, or something else.
Your first pic shows the ceiling to wall relationship with a bow in the ceiling, is this quite solid to the joists?
Your second is showing a fairly normal crack but, how long has the crack been visible, what other, if any, works have been undertaken recently regardless of relating to the crack/bow??...pinenot

Lath and plaster for sure, more than likely the plaster has come away from the laths.

It'll be coming down any day....

If it was my ceiling, bite the bullet, pull it all down (a very messy job, I once spent 6 weeks pulling down lath and plaster walls and ceilings when converting a load of old houses into flats) replace with plasterboard.

There are ways to repair, but once it has started to fail........

http://handycrowd.com/how-to/plasterwork/repair-lath-and-plaster-ceilings/

here's a few ideas on repair....