My house was built in 1949 and the walls and ceilings are made of some kind of wallboard that isn't modern gypsum sheet rock. It's thicker and crumbles a bit like plaster and the filling is gray in color and grainy. Some wall/ceiling surfaces also have been coated with a pretty thick (1/32" or more) coating of something that chips and flakes when damaged but doesn't crumble or make dust.

When I bought the house, there was a thin crack running the length of the kitchen ceiling. I didn't think anything of it. There are three or four similar cracks, of varying lengths (depending on the wall/ceiling they're on) but mostly they're all quite long.

Last night, I noticed a new crack running horizontally along the length of one wall of the dining room and I began to be concerned. I picked off a few chips of the coating. The crack is deep enough to go through the coating, but I see no damage to the not-sheet-rock panel beneath. There is no joint beween panels under the coating where the crack is.

In a newer house, I might assume the house was "settling", but this house has had 60 years to do its settling. Here's my thought, some years ago, the house was attacked by termites. It was treated and there is now no sign of active infestation. The house inspector stabbed the ground-floor floor joists and claimed they had not been damaged, but I have found 2 x 4's around ground floor radiator openings that were destroyed.

Is it reasonable to think that the house is shifting in response to old termite damage? Is there another, more likely reason for the appearance of new cracks?