I found out how to hang posters on cement cinder block walls. I laminate my posters and put masking tape on the edges of the backside. I put white school glue on the tape and hold it on the wall for about thirty seconds. Sometimes they slide a bit but they usually stop after a minute or two. At the end of year, my posters come right off the wall. I'm careful when I remove them because sometimes a little paint comes off the wall too.