Although more than 8,000 varieties of dimension stones supposedly exist in the world, most are varieties of marble, granite, limestone, sandstone, and slate. Which type of stone should you use? It depends on the use. No stone application works equally well in all applications. WATER PROBLEMS Moisture can destroy stone in several ways: Absorbed moisture can freeze and cause spalling in some stones. Salts and pollutants carried by moisture can cause efflorescence and spalling. Porosity, permeability, absorption, and capillarity of stone are, therefore, important considerations in any exterior application. National Bureau of Standards tests found slate to be the least permeable building stone, followed by granite, marble, limestone, and sandstone. FLOORING Stone used for commercial flooring must have good abrasion resistance to foot traffic. It should have a minimum rating of 8 or 10 as determined by ASTM C 241. It also should resist staining. Stone flooring problems increase as the thickness of the stone decreases.