Though concrete blocks are used to create strong, long-lasting structures that meet a number of residential and business needs, they're often finished in some manner to create an attractive facing. One finish that's popular is natural stone cladding. By adding a natural stone cladding you create the appearance of a wall built entirely of that natural stone. It's a way of enjoying the beauty of natural stone while applying just thin stone slices to the block wall surface for a tremendous cost savings.
Cover the surface of the blocks with 3.4 expanded metal lath, a metal mesh created from an expanded perforated metal sheet. Overlap the lath where the sheets join, overlapping 6 inches on vertical seams and 2 inches on horizontal seams. Cut the lath where necessary, using tin snips, and attach the lath to your installation surface using 3/4-inch steel hardened concrete nails.
Mix a thin mortar to the consistency of a thick batter in a bucket using an electric drill with a paddle-bit attachment. Spread the mortar over the lath, covering the surface completely until you have a level layer over the lath. Cover the mortar with a series of scratches using a mason's scratcher to create a scratch-coat surface suitable for the adherence of the adhesive for the stones. Wait 48 hours for the mortar to dry.
Mix a second batch of mortar, this time the consistency of peanut butter. Attach the stones to the scratch coat of mortar by spreading the mortar along the rear of the stones and pressing the stone onto the wall. Mount the stones beginning at the top of the wall and working your way to the base in rows. Wiggle the stone slightly during attachment to help bond the two mortar layers. Place the stones covering the entire surface, cutting them when needed with a wet saw. Wait an hour for the mortar to dry, holding the natural stones in place.
Use a rounded stick to push mortar into the joints between stones to the base of the stones on the blocks. Remove any excess mortar by raking it out with the stick end. Remove the excess mortar from the surface of the stones using a wire brush.
Grout the joints between the stones if desired, using a grout bag. Make a hole in a corner of the bag about 5/8-inch wide and push the nozzle through the hole. Fill the bag to the halfway mark with a grout made of 1 part Portland cement and 2½ parts sand. Roll the bag from the end tightly. Place the nozzle of the bag into the joint and squeeze the body of the bag to push the grout into the joints between the stones to the level desired. Allow the grout and mortar 10 days of drying time.