Ensure that the exterior wall is clean and dry. Try to wait at least 24 hours after a rainstorm before beginning this project.
Apply construction adhesive to the exterior wall and immediately place plastic sheeting over it, smoothing the sheeting out with your hands. This plastic sheeting provides a moisture barrier between the exterior wall and the decorative rock veneer.
Spread a layer of mortar over the plastic. Smooth the mortar out with a cement trowel until it is relatively level. The smoother the mortar is, the more contact the decorative rock veneer pieces will have with the mortar. Allow the coat of mortar to dry for 24 hours.
Back butter the back of your decorative rock veneer with mortar using a putty knife. Press the veneer against the exterior wall, holding it firmly in place for one minute.
Continue placing pieces of veneer until your exterior wall is covered with the decorative rock. The veneer pieces are generally cut so that the rocks appear random, so working straight across the wall shouldn't present any problems. Allow the decorative rock veneer to cure for 24 hours.
Using the same mortar mix that you used to attach the veneers, grout between the veneer panels. Pull a fair amount of grout across the stones in a diagonal manner with a rubber grout float. Once the gaps are filled, allow grout to set for 20 minutes. Wipe the stones with a damp cloth to remove excess grout and allow the grout to dry for 24 hours.