We've been in our house about two years now. Our living room has a fireplace with two small windows on either side about 2/3 up the wall. I noticed that there were cracks in the plaster coming from the upper corners of the wall to the windows, then from the windows to the top of the fireplace mantle. Also, the is about a half inch gap between the fireplace and the mantle by the wall.
I patched the cracks about 18 months ago and they started reappearing within 3-4 months after patching. At the time I talked to several folks (even posted on this board) and the feeling was that I either had some slight movement in the wall or something was sinking.
Back in January I started testing by putting masking tape with lines drawn on it on both the wall and the fireplace. There was zero movement up until about a month ago. Now the lines are seperated by about the vertical width of the line, with the line on the fireplace being lower.
Is this an indication that my fireplace and chimney are sinking? If so, what should I do? I have some experience with sagging floors, decks, etc., but the thought of a sagging chimney scares me.