hi there, we had an extension to the back of our house 12 months ago and karndean throughout (the existing and new part of the house downstairs). In the last two weeks this line has appeared where the new extension meets the old house and there is a ridge in the floor. A friend has said that the concrete floor has dropped and this will be a crack underneath. My question is how can this be rectified, whose fault is it and will it get worse if left? the karndean cost £3200 and was a installer from a showroom that stocks karndean. your thoughts would be much appreciated.