Clean the wall and the stone veneer of dirt and debris with water and a brush. You want a clean surface before adhering the rocks to the wall to create the facade.
Trowel mortar onto the wall roughly a half inch thick.
Dip a single stone into water to dampen the backside. Apply a coat of mortar to the back of the stone.
Press the stone into the mortar. Twist the stone as you press. Repeat the process to create the artificial rock facade, placing the stones ⅜ to ½ inch apart. Remove excess mortar in the joints before the mortar sets.
Fill in the joints between the stone veneer pieces and adjacent walls with a grout bag. Allow at least two hours for the mortar to set.