When installed properly on an exterior wall, manufactured stone is practically indistinguishable from real stone. Even the feel to the touch is very realistic. With the new types of manufactured stone available, if the finished wall does not look like real stone, it is because of installation errors. When installed properly, it should last a lifetime, which is good because manufactured stone is not inexpensive, costing about $6 to $10 per square foot.
Manufactured stone is made from lightweight concrete. This is basic concrete with lightweight fillers mixed with it. The forms for the stones are made from casts of real stones. The major manufacturers have many hundreds of different molds for a random selection of sizes and shapes. The fronts of the stones are colored and the backs grooved, so they adhere well to the mortar.
First, make sure the sheathing on your house is in good condition once the old siding is removed. Attach two layers of heavyweight (30-pound) builder’s felt to the wall sheathing. Use some type of membrane if the stone will run up to any window or door openings. Peel and stick membrane is easy to work with.
The next step is to attach metal lath over the felt. The lath provides a good, strong surface for the mortar to flow through. When you screw the lath to the wall, try to keep it as smooth and tight as possible. One way to do this is to locate the screw in one corner of an opening in the lath. Locate the next screw in the opposite corner of another opening to stretch the lath tight.
With the lath in place, it is time to apply the mortar. First, spread a medium-thick layer of mortar over the lath. Put another layer on the back of the stone so it covers the grooves. Press the stone into the mortar on the lath for the first bottom course. For each additional course, tap the stone back somewhat even with the first course and downward against it. The mortar should ooze out.
You must decide on the width and depth of the mortar joint between the stones. A one-half-inch wide joint is typical for exterior stone surfaces.
For a very rustic appearance, use three-quarter-inch width joints.
The depth (rake) of the mortar joint also affects its functionality and appearance. Any rake can be used for indoor applications. For exterior use, a standard rake is good where the mortar is just slightly below the surface of the stone. Flush joints give a smoother appearance and shed water well.
Overfilling the joint so the mortar sticks out creates a rustic look.
There are several options for working the mortar between the stones. If you work it almost immediately, the mortar joints will have a smooth appearance. The longer you wait, up to several hours, the rougher the surface texture of the joint will look.
