Sanding marble is a time consuming process. This will require using a wet sanding process to achieve the desired results. While this method will work fine for statues, tile and marble countertops, sanding large areas of marble, like marble floors, requires a completely different process and technique. Knowing how to do this allows you to polish hand cut and rough edges to really make your marble job shine.
Start with the coarsest grit sandpaper you have. Wrap it around a block of wood or sanding sponge. Wet the surface of the sandpaper and marble. Begin sanding. Note use 220 when trying to smooth out irregularities. For small blemishes uses 400 grit. For anything else start with 600.
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Progress through the grits, using a higher number until you reach 1600 or 2000 (or stop whenever you like the look, even if it is only at 600 grit). Make sure to keep the sanded area wet or you could 'burn' the marble. By now your marble should be taking on a highly polished sheen and be free of surface blemishes.
Seal the sanded area. Use a marble sealer and apply it liberally with a rag. Wait the indicated amount of time and wipe off any excess with a clean, white cloth.