The adhesive on the back side of the Aspect tiles is highly aggressive and pressure sensitive. Proper wall preparation is required. Aspect can be installed over most structurally sound substrates if they are clean, flat, smooth, dry and free of dust, wax, soap scum and grease. 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-grit sandpaper. Also, to prevent the color of your wall from showing through the seams of your Glass Aspect installation, one coat of paint (in the finish of your tiles) can be applied to your wall before installation.