I had a problem with my shower tile and grout so I tore the old tile down. What I have now is the old mastic and some torn drywall paper on the wall. The gypsum is not really showing though. I want to put some solid shower panels up now. Do I need to put up a vapor barrier on the wall? And if yes (or no for that matter) how will I get the new solid panels to stick to such a surface? Can I just attach the panels with a few screws and caulk over the screw holes? This house is 7 years old. Thanks a million.