You?re right. Lath and plaster ceilings can be very brittle especially in older properties and any work or activity in the loft can result in several heavy plaster showers!
The problem occurs because the nibs formed when the plaster was originally applied to the lath can easily get broken especially when laying down loft boarding. If the nibs are broken than the plaster will drop or crack.
It is possible to strengthen lath and plaster ceilings by screwing or nailing (with plasterboard nails) the plasterboards into the joists above the ceiling to add extra strength. Additionally, plaster washers can be used to strengthen the ceiling if the plaster has started to separate from the lath.
