Cinder block walls - need hanging and acoustic advice My room walls are cinder-block! The ceiling is high. Sound echos (did I spell the correctly). What can I do to absorb the sound? What sticky stuff attaches to cinder blocks? I would like to hang up posters and not have to re-attach them b/c they fall down after a week. Masking tape doesn't work (what DOES work with masking tape... even the post office asked that I not use it b/c they say it falls off). Duct tape will leave residue that I would have to clean off at the end of the year (but will it work on cinder block?). Oh, and the teacher before me used painter's tape on the white boards. I took it down but now there's sticky residue where the yellow tape was (but not where the blue was)!