Absolutely. Have you ever noticed the effect created upon a piece of sandblasted marble, limestone or granite after it has been sprayed with water? A very light material will take on a dark gray or black appearance after the water has penetrated! Yes, moisture will indeed penetrate these substrates and, compounding this porosity, is the fact that some marble, limestone and granite panels are usually a mere 1 to 1.5 inches thick.
It certainly does not take long for absolute water transmission through the substrate. Cautionary note, test the application of any material upon these substrates, as they may effect the appearance of the stone. Due to its specific formulation, KL-25 is normally recommended for stone applications. A small test sample should always be applied prior to commencing the entire application.