Although marble is a stone, it is actually porous and absorbs liquids. When a darker liquid is spilled onto marble, the surface will stain. On decorative marble, such as fireplace mantels, this isn't a serious problem. But on working marble surfaces, including kitchen or bathroom countertops, a stain will ruin the appearance unless it can be sanded off. Fortunately, marble can be sealed to prevent staining so that the beauty will never be compromised.
Clean the marble surface with a soapy water solution and a sponge. Any type of dish-washing soap will work well, but if this is a marble countertop in a kitchen that has been exposed to cooking oils, a soap formulated to remove grease is the best choice. After the surface has been cleaned, rinse the marble with fresh water and allow it to dry thoroughly.
Tape off any areas around the marble that you don't intend to seal. This will include all chrome, stainless steel or wood that is directly adjacent to the marble surface. Use a high-quality painter's masking tape for this task.
Spray the marble surface liberally with sealer. Sealer for marble is available at hardware stores. Make sure the surface is completely wet and allow the sealer to remain on the marble for approximately 15 minutes to 30 minutes.This will give the liquid time to soak into the marble surface. If in doubt about the time needed, check the sealant manufacturer's instructions.
Wipe the surface off after the required saturation time using a clean, dry, cotton shop towel or shop cloth. If this is a large surface, you may need to use several shop towels. Make sure the surface feels dry after the sealer has been removed.
Apply another coat of sealer for added durability, especially if this is a working marble countertop. Wait until the first coat is completely absorbed, which will take about 30 to 40 minutes. Apply the second coat of sealer liberally, wait 15 to 30 minutes and wipe the excess off with your shop towels.
Allow the surface to cure for about six to eight hours before use. A full cure will take place, depending upon humidity and usage, between 24 hours and 72 hours. Avoid heavy use until then.