If you are planning to install glue up tiles to your ceiling, you need to make sure your ceiling is clean. We recommend that you apply a fresh coat of primer or paint on the ceiling before the panels are installed. Also, be sure to clean the back of each panel with rubbing alcohol before applying adhesive. Acceptable substrates are drywall, plaster or clean, smooth tile (glazed, porcelain type tile; not porous or textured). Any damaged, loose or uneven areas must be repaired, patched, leveled and primed. Fill cracks and irregularities with wallboard compound or spackling, then sand smooth with fine-grade sandpaper. Any porous material like highly textured drywall, plywood (or any raw wood without primer), and wallpaper unless removed, sanded and primed, will result in adhesive failure.