Removing cement that sticks to granite surfaces takes a specialized acid cleaner. Outdoor cement projects, or indoor projects such as grouting tiles in the bathroom or kitchen, are usually messy jobs. The cement can drip or smear on nearby surfaces, such as granite countertops. Cleaning it immediately, though the best choice, isn't always an option. A little brick acid and sealer will bring back the beauty of granite.
Pour a small amount of brick acid in an inconspicuous area of the granite surface to test the product. Follow the product label instructions. Most brands come prediluted, but some require mixing the solution with distilled water.
Pour the brick acid directly onto the cement that has adhered to the granite. Allow 15 or 20 minutes for the acid to soak on the surface if the cement is hardened, or three to five minutes if the cement is still wet.
If you are treating an exterior granite surface, rinse it with a pressure washer set at 800 psi (pounds per square inch). Rinse interior granite surfaces with a sponge and cold water.
Let the granite dry completely.
Apply a granite sealer with a large paintbrush. Follow the label directions for proper drying times. Exterior granite will dry much quicker than interior.
Buff the surface with a soft towel when it is dry for a nice finish.