If you're planning to tile your fireplace, you'll need to start with a clean slate. Whether your marble is discolored from soot or needs a good deep cleaning, you'll want to take care of that before tiling. The good news is that marble is a fairly easy material to clean, as long as you use the right products and techniques. A paper towel, cotton ball, or white terry cloth towel soaked in liquid bleach can be used to clean marble tile. Leave it for 24 hours, then remove it and rinse with water. For particularly stubborn stains, repeat this process. Once stains have been removed, wipe down the marble with natural-stone cleaner, followed by a coat of sealant.