There is a lot of controversy over whether or not you need to seal marble and granite counter tops, and if so, how often. First you should do this simple test to see if your stone is already sealed. Bear in mind that the ability to absorb sealer in the first place is due to the porosity of the stone and this varies from stone type to type.

How to test if your marble or granite need to be sealed:

  1. pour a tablespoon of regular tap water onto the counter and let it sit for 10-15 minutes
  2. Wipe away water with a dry cloth
  3. Is there a darkening of the stone?
  4. If there is darkening, your counters could use some sealer.
  5. If color hasn’t changed, the stone is sealed.

Most granite is very dense and doesn’t need as much sealer nor does it need to be reapplied often. Certain granite such as Black Absolute shouldn’t be sealed at all. Marble, especially the lighter colors, are more porous and will  benefit from sealing. Just remember sealer DOES NOT PROTECT against etching, sealer will only protect from staining. Stains from red wine, and the like won’t darken the stone if it is protected, but anything acidic can “etch” or erode the  surface of stone leaving a ring or water mark.
For information on how to protect against etching follow this  link to learn about Clearstone coating.
http://bostonstonerestoration.com/clearstone-marble-protector/