Hi. Thank you for the efforts you have gone to, to help. It appears that I have been using the only known solution know 'the sledge hammer' to get rid of them. I have not noticed any missing ceiling, however, up until now I had not thought to look. I did have one that was particularly difficult to get rid of under a bridge which is over a pond. It was submerged below the water. I was able to get it to emerge by placing foundations then deleting one foundation square at a time and when the 'sheet of paper' reappeared above the water line I then was able to remove it (deleting the blocks of foundation together did not work as the sheet of paper returned under water). Thanks Again BillFlowerpot