Re-tiling a shower is a great way to take a dated bathroom into the 21st century without making any structural changes. If you are installing over an existing surface you will need to make sure that the surface is free of any imperfection and clean of debris. Sometimes imperfections can be solved by patching with a waterproof patching compound. Remove all grease, oil dust, sealer or curing compound by sanding, scraping or chipping away any contaminants.