For marble cleaning the best acid-based stone cleaners cannot be used. You are limited to (alkaline-based) cleaners which are made from sodium carbonate/hydroxide/hypochlorite/anionic/nonionic surfactants/citrates/glycol ethers/alcohol/sodium sulfates to name a few. Home Depot carries their "Zep" product line of cleaner/degreasers which are formulations based on these chemicals.If you have existing stains, mold,grout grime, or a yellowing of your marble this must all be removed before any sealing preservation otherwise the discoloration will be trapped under the sealed surface. If your marble is new or "like new" in appearance and has been washed, rinsed, and dried completely then proceed with sealing preservation. "Dupont Stonetech Professional Bulletproof Sealer" is by far the best sealer and does not change the marble's appearance. Since it is an impregnating sealer it will not coat the surface and will allow the stone to breathe. There are epoxy coatings to make marbles resistant to scratching and bruising but they are difficult to apply on vertical surface, costly, and make the marble non-breathable. Breathability is important to allow moisture vapours and mineral gas exchanges from behind and inside your marble to be released. Hope this helps! info@rmstoneworks.ca