I think Nige F is right about not worrying too much over the roof but it's always wise to find out if the structure needs strengthening to accommodate the extra weight of concrete tiles before replacing slate. (Maybe you did?) I only mentioned the roof because a crack that is widening to 3/16" does sound like a little more than the movement you would normally expect in a lath and plaster ceiling, although, on the joint of a slope, is possible.
As said, it's not going to collapse but it is worth asking a question in one of the other forums just to put your mind at ease. If any work is required, just make sure you know exactly what needs to be done and is exactly what you get for your money.
I hope it is just settlement and that the bonding/filler solves the problem, if only in the short term.
As said, it's not going to collapse but it is worth asking a question in one of the other forums just to put your mind at ease. If any work is required, just make sure you know exactly what needs to be done and is exactly what you get for your money.
I hope it is just settlement and that the bonding/filler solves the problem, if only in the short term.