I have just finished painting two rooms in my house. Above a framed opening leading from kitchen to family room the wall had cracked, possibly poor support. I plastered and sanded it repeatedly until it stopped cracking. Now the rooms have been painted for 2 weeks and the crack has come back on both sides of the wall. What could I have done to avoid this. How can I repair it now or the next time I paint. Someone suggested caulk but how can you sand that smooth to paint and someone else suggested white glue. What do you think?