Manufactured stone veneer offers builders and homeowners the look of natural stone at a fraction of the weight and cost. Also called cultured stone or artificial stone, this product has evolved significantly since its introduction. When installed correctly, manufactured stone can deliver decades of service and closely mimic the appearance of quarried stone. This article covers the essential techniques for working with this versatile exterior cladding material.
Understanding Manufactured Stone Products
Composition and Manufacturing Process
Manufactured stone is a cement-based product made from Portland cement, lightweight aggregates, and iron oxide pigments. The mixture is poured into polyurethane molds taken from real stone. This process captures every detail of the natural stone surface texture, from lichen growth patterns to subtle grain variations. After casting, the stones cure for 24 to 48 hours before being palletized and shipped.
The lightweight nature of manufactured stone is one of its primary advantages. A square foot of manufactured stone weighs about 5 to 8 kilograms, while natural stone can weigh 25 to 40 kilograms per square foot. This reduced weight means standard wall framing can support the veneer without additional structural reinforcement in most residential applications.
Types and Profiles Available
Manufacturers produce a wide variety of stone profiles to suit different architectural styles:
- Ashlar patterns: Rectangular stones in varying sizes arranged in a running bond pattern, suitable for traditional and formal architecture
- Rubble or fieldstone: Irregular shapes that mimic natural fieldstone walls, ideal for rustic and cottage-style homes
- River rock: Smooth, rounded stones that resemble creek bed stones, often used for accent walls and chimney surrounds
- Ledge stone: Flat, stratified pieces that create a stacked appearance, popular for contemporary and modern designs
- Corner pieces: Preformed L-shaped units that wrap around outside corners, eliminating the need for miter cuts
Color options range from warm earth tones like tan, brown, and buff to cooler grays, charcoals, and bluestone hues. Many manufacturers offer color-blended palettes where individual stones vary slightly within a consistent family, creating a more natural appearance than uniform color.
Surface Preparation and Substrate Requirements
Creating a Proper Base
Manufactured stone requires a solid, stable substrate. The installation surface must be structurally sound and capable of supporting the weight of the veneer plus the mortar. Common substrates include:
- Exterior-grade plywood or OSB sheathing covered with building paper or felt
- Concrete or masonry walls with adequate bonding surface
- Metal lath attached over approved weather-resistant barriers
- Portland cement board installed per manufacturer specifications
Installing the Weather-Resistant Barrier
A weather-resistant barrier is mandatory behind manufactured stone veneer. Two layers of Grade D building paper or a single layer of house wrap approved for use behind masonry veneer should be applied. All horizontal seams must overlap by at least 6 inches, and vertical seams by at least 4 inches. The barrier should extend into window and door openings to direct any moisture that penetrates the veneer back to the exterior.
Metal Lath Installation
Self-furring metal lath provides the mechanical key for the mortar scratch coat. The lath must be attached with corrosion-resistant fasteners, typically 1-inch-long galvanized roofing nails with 3/8-inch heads, driven into the wall framing at 6-inch intervals vertically and 16 inches horizontally. Lath sheets should overlap by at least 2 inches at vertical and horizontal joints. At outside corners, bend the lath around the corner to maintain continuity.
Flashing and Weep Screed Requirements
Proper drainage behind the veneer is critical for long-term performance. A weep screed must be installed at the base of the wall to allow moisture to escape and to provide a clean termination point for the veneer. The weep screed should be placed a minimum of 2 inches above finished grade and 4 inches above concrete surfaces such as driveways or patios. Additional flashings are required above windows, doors, and at roof-wall intersections.
Mortar Mixing and Application
Scratch Coat Application
The scratch coat forms the base layer that bonds the stone to the wall. Mix Type N or Type S mortar to a stiff consistency similar to clay. Apply the mortar to the metal lath with a trowel or hawk, forcing it through the lath openings to create a mechanical bond. The scratch coat should be approximately 1/2 inch to 3/4 inch thick. After application, scratch horizontal grooves into the surface with a rake tool to create a mechanical key for the setting bed. Allow the scratch coat to cure for 24 to 48 hours before installing stone.
Setting Bed Mix
The setting bed mortar should be slightly looser than the scratch coat. Mix in small batches that can be used within 30 to 45 minutes, as mortar begins to set quickly in warm weather. The mortar should be applied to the back of each stone piece before pressing it into place. This back-buttering technique ensures maximum bond strength and fills any voids in the stone.
Grouting and Joint Finishing
Mortar joints in manufactured stone work serve both structural and aesthetic purposes. The table below shows recommended joint sizes for different stone types:
| Stone Type | Joint Width | Joint Depth | Tool Type |
|---|---|---|---|
| Ashlar patterns | 1/4 to 3/8 inch | 3/8 to 1/2 inch | Pointing trowel |
| Rubble or fieldstone | 3/8 to 1/2 inch | 1/2 to 5/8 inch | Gauge trowel |
| River rock | 1/2 to 3/4 inch | 5/8 to 3/4 inch | Slicker trowel |
| Ledge stone | 1/8 to 1/4 inch | 1/4 to 3/8 inch | Joint filler |
Joints should be finished with a tool that matches the stone style. A concave joint is traditional for most manufactured stone installations, while a flush or raked joint works better for rustic styles. Avoid smearing mortar on the face of the stones. If mortar does get on the stone face, allow it to partially dry before brushing it off with a stiff brush.
Stone Layout and Installation Sequence
Preparing the Layout
Before mixing any mortar, lay out the stones on the ground in front of the wall. Pull stones from several boxes to blend colors and sizes evenly across the wall. Most manufactured stone is packed with color variations within each box, but blending multiple boxes prevents concentration of any single color. Arrange the layout to avoid long vertical joints, clustered patterns of the same color, and running bond alignments that create visual lines.
Installation Sequence
Follow these steps for a systematic installation:
- Begin at the bottom of the wall and work upward, starting from a corner if possible
- Apply mortar to the back of each stone (back-buttering), covering at least 80 percent of the surface area
- Press the stone firmly into place with a slight twisting motion to ensure full contact
- Maintain consistent joint spacing using plastic wedges or joint spacers if needed
- Install corner pieces first at outside corners, then fill in with flat pieces
- Cut stones as needed with a masonry saw or angle grinder fitted with a diamond blade
- Step back frequently to check for pattern and color balance across the wall
- Allow the mortar to set for 30 to 45 minutes before tooling the joints
Cutting and Shaping Stone
Cutting manufactured stone requires the same tools used for natural masonry work. A wet saw with a diamond blade produces clean, dust-free cuts ideal for exposed edges. For on-site adjustments, an angle grinder with a dry diamond blade works well for notching stones around outlets, pipes, and other penetrations. When cutting, always wear eye protection and a respirator, as the silica content in the cement can create hazardous dust.
For small nips and shaping, masonry nippers can snap off small pieces from the edges of stones. This technique is useful for fitting stones into tight spaces without generating dust. Score the stone with the nipper jaw first, then squeeze firmly to break along the scored line.
Sealing and Curing
Manufactured stone does not require sealing for structural performance, but a penetrating sealer can help resist staining and simplify future cleaning. Wait at least 28 days after installation before applying sealer to allow the mortar and stone to fully cure. Use a breathable, water-based sealer designed specifically for masonry products. Avoid film-forming sealers that trap moisture behind the stone surface.
Proper curing is essential for mortar strength. The installation should be kept moist for at least 48 hours after completion, especially in hot or windy weather. Light misting of the wall twice daily prevents the mortar from drying too quickly, which can lead to reduced bond strength and cracking. In cold weather, protect the installation from freezing for at least 48 hours using insulating blankets.
Manufactured stone offers an excellent balance of aesthetic appeal and practical performance for exterior walls. By understanding the material properties, preparing the substrate properly, and following correct mortar and installation techniques, builders can achieve results that rival natural stone at a lower cost and weight. For more information on related materials, see our guide to exterior cladding systems, compare natural building stone types, or explore brick veneer installation methods as alternatives to manufactured stone.