No, only those that are porous. Although it is the hardest stone known to man, its porosity varies from quarry to quarry and from slab to slab. But this characteristic is easily checked by pouring a little water on it in an inconspicuous location. If it sits there for 30 minutes, the countertop does not need to be sealed. If it absorbs rapidly, the countertop should be sealed. We can always help you determine if your countertop you purchase from us should be sealed or not.