I have cracks that appeared after 6 months, and neighbours tell me they have cracks that appear each year. I guess movement of joists, and the changing humidity with season causes walls and ceilings to move. I tried caulk, but did not like the result, so changed to Easi-fill. I am told that Easi-fill has some plasticisers in it allowing it some give. Whatever the truth, it is easy to apply, and it paints well. I also had three long cracks appear in a new ceiling, and some fine cracks in two re-skimmed walls, plus some large cracks near a new boiler flue.