Part of the Ceiling in one of the bedroom needs repair that was plastered before and the plaster is falling off again.
The initial damage was caused probably by a radiator leak from the floor above(damaged ceiling has a living room directly above). Please see two photos of the damage.

1. What is a good way to repair the ceiling and cost?
2. What is the advantage of installing a mesh in the ceiling?

Please feel free to ask any questions or give any suggestions.