I need all of my precious stage space for our production of Cabaret, as the pit will be on stage. So I'm going to keep our back curtain open (we are at a school), and expose the back (black) cinder block wall and music room door. I want the back wall to look like old brick wall with a top edge that looks like it has crumbled away (a way to blend it into the high cinder block walls), and the door to look old as well. I thought cardboard sheets might be the lightest and most economical solution (correct me if I'm wrong), but I need a way to fix the cardboard to the wall so that it does not leave anything behind, but so that it will be permanent enough so as not to come off during the show's run. Any creative solutions?