Faux rock is often made of concrete, and while it may have the size and shape of natural stone, it still has the same dull gray appearance of freshly set concrete. To add more style to your setting, you'll need to change the appearance of the rock. With the same process used to stain colors to concrete slabs, you can also stain your faux rock. A brush and some color will transform your rock, altering its appearance to match your décor and turning that dull gray into a colorful addition that serves as an accent piece.
Clean the surface of the faux rock with a liquid soap and water mix. Use a scrub brush to remove any dirt or debris, and then rinse the cleanser away with clean water. Pat the rock dry with a piece of cloth.
Put on a pair of rubber gloves to protect your hands from the stain. Apply a layer of acrylic-based concrete or faux rock stain using a foam applicator. Spread the stain over the rock, covering the entire surface with an uneven layer of the stain to create a mottled, more natural color distribution. Use an earth-toned color of stain or gray for a natural look. The heavier you apply the stain, the darker the color. Allow the stain to dry for two hours.
Apply additional patches of stain onto the first coat using the applicator. Use a random coverage pattern for a natural appearance. You can use the same color as the first stain or apply a new color of stain that's lighter than the first to build up the natural stone appearance. Allow 24 hours for the last layer to dry.
Brush a coating of concrete sealant over the stain using a foam applicator — this will protect the color. Use a matte sealant to avoid creating a glossy look for the rock.