Masonry Magic

Installing Manufactured Stone Products

By Fernando Pagés Ruiz
Spring 2003

Since antiquity, the hardness, durability, and beauty of stone represent the best in building materials. But natural stone has become hard to find, and expensive to purchase. So, it’s not surprising that builders have turned to artificial stone products to satisfy the demand to create affordable stone surfaces. The good news is that manufactured stone no longer looks artificial. Molded from true quarried materials and fieldstone walls, manufactured stone has become virtually indistinguishable from the real thing.

Field stone, lime stone, river rock, split rock, red rock, or ledge stone – it doesn’t matter what style, region, or theme you’re trying to emulate – there’s a manufactured product line to match it. You can create a dry-laid look without grout joints between the stones, or fill the joints with grout. You can even find fieldstone with simulated moss on them.

The components of manufactured stone include Portland cement, mineral oxide colors and lightweight aggregates. And manufacturers can ship these light and easily-packaged products just about anywhere in the United States. It’s no wonder the trend toward stone facing has revived nationwide.

Installation is Easy and Quick

You can install manufactured stone on interior and exterior applications over most types of construction surfaces. You don’t need wall-ties, footings or special structural support to hold the stone — even in earthquake regions. You can install manufactured stone over clean and untreated concrete or masonry surfaces without any special wall preparations. But on building surfaces such as wood studs, plywood and drywall, you have to construct a rigid mud-base subsurface similar to that needed for installing split-brick or ceramic tile.

Prepare the surface: To install manufactured stone onto open studs, you’ll need to apply paper-backed, galvanized, ¾-pound rib, expanded-metal lath nailed to your studs with galvanized nails or staples. Nail the lath every six inches vertically, and 16 inches horizontally with nails that penetrate at least 1 inch into the studs. Overlap your paper two inches horizontally and overlap the lath by at least ½ inch. On vertical end-joints, lap your paper 6 inches and the lath at least 1 inch. Then apply a ½-inch thick scratch coat of mortar over the lath and allow it to cure 48 hours before installing the stone.

Over wallboard, plywood or rigid insulation board, start by covering the wall with a weather-resistive barrier, such as Kraft waterproof building paper or asphalt-saturated rag felt. Apply the weather barrier horizontally, and install 2.5-lb. or heavier diamond mesh, expanded galvanized metal lath over this barrier with galvanized nails or staples. Apply a ½ in. scratch coat of mortar over the lath and allow it to set.

Lay out the stone: Before you start mortaring stones onto the wall, lay out about 25 square feet of stone on the floor near your work area. This allows you to play with the fit and color patterns before you set the stones in place. You’ll want to achieve a balanced pattern of shapes, sizes and colors on the wall. It’s easier to do this when you have a pre-arranged area of stone to choose from, instead of just grabbing whatever stone comes next from the box. When working with several crates of stone, mix and select pieces from different boxes. This helps assure a better blend for a balanced appearance.

Get started: Unlike other masonry, you install most manufactured stone starting from the top of the wall and working downward towards the bottom. These stones are light enough to stick without support and by starting at the top, you avoid dripping mortar onto finished work areas below. If you are laying stone to achieve a “dry-stack” appearance you will have to install stone courses starting at the bottom, and work carefully to avoid staining the stone with dripping mortar as you work your way up the wall.

Either way, before you get started installing stones on the open areas of the wall surface, install your corner pieces. This makes it easier to fit your other stones into place later. Corner pieces come with a short and long returns; alternate these in opposite directions on the wall.

If any mortar accidentally gets on your stone face, don’t wipe it off with water. This will only smear and stain your surface. Instead, allow the mortar to dry and then brush it off with a dry whiskbroom.

Fitting: When working with quarried stone styles, you’ll need to keep the courses level. Snap chalk lines about every four to eight as a guide, and then use a small level to set each piece.

Don’t forget to stagger joints both vertically and horizontally. Stones look best with uniform grout lines of about ½ in. or less. Avoid long, unbroken grout lines when placing fieldstone, river rock and other variable-sized stones.

Trimming: You can cut and shape stones with a brick hatchet, wide-mouth snips, or by striking them with the edge of your trowel. For long, straight cuts use a circular saw with a diamond masonry blade. Although good quality manufactured stone has uniform coloring all the way through, you should always turn any cut edges away from view.

Appling mortar: Using a mason’s trowel, coat the back of each stone with a ½-inch thick layer of mortar and then, using a gentle wiggling action, press the stone firmly into place. It’s okay to allow a little mortar to squeeze out along the sides of the stone.

It’s especially important to make sure there’s enough mortar behind every stone when laying up a jointless dry-stack installation, since the bedding mortar must hold the stone without grout. Apply a generous amount of mortar to each stone and then clean off the excess with a margin trowel, making sure to fill any voids.

If you’re setting manufactured stone on a hot day or in an especially dry climate, it’s a good idea to dip each stone into a container of water and then let it dry a few minutes before placing it on the wall. When working with jointless dry-stack materials, you should dampen the stones regardless of the weather conditions.

Grouting: After your stone has set, carefully apply mortar using a grout bag, taking care not to smear grout onto the stone surface. Once the mortar joints have become firm (after about 30-60 minutes), use a wooden or metal striking tool to rake out excess mortar and work grout into the joints to thoroughly seal the edges.

Cleaning and sealing: After finishing the grout lines use a whiskbroom to smooth the joints and clean off loose mortar. At this point, brush off any drops and spots, which should come up easily. Never use a damp sponge to clean the surface or you’ll stain the stone permanently. And don’t use a wire brush or acid.

Fernando Pagés Ruiz is a builder and writer in Lincoln, Nebraska.