On concrete block walls or unpainted brick walls the stone can be stuck directly to these surfaces without any additional layers needed.
On wood or drywall add a layer of tar paper starting at the bottom and working upward over laping the paper by 4″. The paper can be attached with a stapler because a layer of expanded metal lath is the next layer needed. This should be installed from the bottom working up and over lap by a couple of inches. Use nails or screws that will go into the studs by an inch and half. A tip here would be to add a washer to you nail or screw to help hold on the lath. Fasten the lath on every stud and not more than 8″ apart. Wear gloves to work with the lath it will chew up your hands as you work with it.
Cover the lath with a ½” coat of mortar or scratch coat and allow to dry for about an hour. When applying the scratch coat use a course brush to form grooves in the mortar so you next layer has something to grab on to. The mortar should be one part type “N” cement and 2 parts mason sand. Mix with enough water to form a putty consistency this formula can also be used to set the stones and grout the joints.
Applying the stone
Most stone veneer is easily shaped or cut as needed. Cutting or shaping can be done by using a circular saw with a masonry blade, a wet saw, or grinder with masonry cutting wheel or diamond edge. A hammer and chisel will cut the stone, tap the chisel on the stone until it splits.
Butter the stone by adding about a ½” to ¾” of mortar on the back of each stone before sticking them to the wall. Start at the bottom and firmly push the stone into the wall causing the mortar to squeeze out on the edges of the stone. If the stones are shifting when you let go of them your mortar may be too thin and you will need to add some more cement and sand till it is sticky. I have found that adding some masonry lime to the mix will make the stones stick better.
As you work up the wall you can use some wooden or plastic spacers to help hold the stones until the mortar dries.
Be careful not to be too messy with the mortar and get it all over the show side of the stones. You need to keep them as clean as possible for the best finish.
Getting your joints right
After about an hour, when the mortar has dried a bit, push the mortar into the joints this can be done with a jointing tool or a rounded stick. I have found and old spoon or even a kitchen knife works good for this.
After the above has been completed, wire brush any excess mortar from the face of the stone, and clean up joints with the wire brush and a whisk broom.
Now it is time to grout the joints and for this you will need a grout bag. Mix the mortar until it is a little runny and fill the bag half way roll the bag and squeeze with your other hand forcing the mortar into the joints. The hole in the bag shouldn’t be more than ¾”.
If you don’t grout the same day make sure you leave your stones clean and wire brush any mortar off of the face of the stones before the mortar hardens.