Wash off the wall and the back of the stones with a mild cleanser to provide a cleaner surface for the mortar to adhere to.
Mix a batch of mortar that contains 2 parts of washed sand and 1 part of Portland cement, stirring it for about 5 minutes until it's about as thick as mashed potatoes.
Spread water onto the back of the first stone you're installing with a masonry brush. This prevents the stone from drawing moisture out of the mortar, which can cause it to crack.
Cover the back of the stone and the spot on the wall where you're installing the stone with a 1/2 inch of mortar.
Push the stone onto the wall, twisting it slightly as you place it. Begin laying the stones in one of the bottom corners, going across the wall to the other side, then working your way up to the ceiling. Cut the stones with a wet saw to fit around light switches, vents and electrical outlets. If any mortar gets onto the front of the stones, wipe it off with the trowel before the mortar can set.
Apply grout to the joints between the stones with a grout bag, then smooth the grout with a joint tool. Allow the mortar to set for the time specified on the packaging.
Cover the wall with concrete sealer to protect the finish of the stones.