Measure the surface area to be covered with thinstone veneer. Trim veneer stone to fit using a wet saw, hammer or chisel. Spread a 1/2-inch layer of mortar directly onto the thinstone with a notched trowel. Tilt the trowel to a 45-degree angle and drag it along the surface of the mortar to raise ridges for better coverage of the unit shell wall.
Place the veneer stone from the bottom up. Apply firmly, with a slight twisting motion to set the stone. Wait an hour for the mortar to begin to dry. Fill the joints between the placed stones with mortar. This will help secure the stones. Remove excess mortar from the surface of the stones. Allow mortar to firm for two hours, and then level the mortar in the joints using a striking tool or stick. Wipe out and remove excess mortar from joints. Compress mortar in joints, making joints an even depth. Allow mortar to set for three weeks, then apply a layer of stone sealant to protect the surface of the stones.