To properly install stone veneer, you typically apply a series of essential layers that provide structural adhesion, moisture protection, and a stable base. This multi-layered system ensures the longevity and stability of your stone veneer wall.
Essential Layers Beneath Stone Veneer
The layers underneath stone veneer are crucial for both its adhesion and the protection of the underlying structure from moisture. Here's a breakdown of the typical components:
1. Structural Substrate
The foundation layer is the wall or surface you're veneering. Common substrates include:
- Plywood or OSB Sheathing: For exterior walls over wood framing.
- Concrete: Poured concrete walls or foundations.
- CMU (Concrete Masonry Units): Cinder block walls.
- Existing Stucco or Masonry: Sometimes veneer can be applied over existing, stable surfaces after proper preparation.
2. Weather-Resistive Barrier (WRB)
Directly applied over the structural substrate, the WRB acts as a crucial moisture management layer. Its primary function is to prevent water that might penetrate the veneer and mortar from reaching the sensitive framing or interior of the building.
-
Types of WRBs:
- Building Paper: Often two layers of grade D building paper.
- House Wrap: Synthetic, water-resistive membranes.
- Fluid-Applied Barriers: Membranes sprayed or rolled onto the surface.
-
Importance: Proper overlapping and flashing of the WRB around openings (windows, doors) are critical to ensure a continuous weather seal.
3. Metal Lath
After the WRB, an expanded metal lath (often galvanized or stainless steel) is mechanically fastened to the substrate. This lath provides a rough, textured surface that creates a strong mechanical bond for the subsequent mortar layers.
- Purpose: The lath acts as a "key" or "reinforcement," allowing the mortar to grip firmly and prevent cracking or delamination.
- Installation: It's typically attached with corrosion-resistant fasteners, ensuring sufficient overlap between sheets.
4. Mortar Scratch Coat
A mortar scratch coat is the fundamental foundation of any stone veneer wall. Applied directly over the metal lath, this initial layer of mortar (often a type S or N mortar mix) is pushed firmly into and through the lath.
- Application: Once applied, the surface is "scratched" horizontally using a notched trowel or special rake. This creates deep grooves and ridges, enhancing the surface area and mechanical bond for the next mortar layer.
- Curing: It's essential to allow the scratch coat to cure properly, usually for at least 24-48 hours, before proceeding.
5. Mortar Setting Bed
This is the final mortar layer applied directly to the cured scratch coat, to which the stone veneer units are adhered.
- Composition: Often a polymer-modified mortar is used to improve adhesion and flexibility, especially for exterior applications.
- Application: Mortar is typically "buttered" onto the back of each stone veneer piece or applied directly to the scratch coat, and then the stone is firmly pressed into place.
Summary of Layers
Here's a quick overview of the typical layering for stone veneer installation:
| Layer | Purpose | Application Method |
|---|---|---|
| Structural Substrate | Primary wall structure (e.g., plywood, concrete) | Existing structure |
| Weather-Resistive Barrier | Moisture protection; prevents water intrusion | Rolled/applied over substrate, fastened |
| Metal Lath | Mechanical key for mortar adhesion | Fastened securely over WRB |
| Mortar Scratch Coat | Foundation; textured bonding surface | Troweled over lath, then scratched |
| Mortar Setting Bed | Adheres stone veneer units | Troweled onto stone backs or scratch coat |
| Stone Veneer | Decorative finished surface | Pressed firmly into setting bed |
Additional Considerations
- Weep Screed: For exterior applications, a weep screed is installed at the bottom of the wall, allowing any moisture that gets behind the veneer to escape.
- Control Joints: For large surfaces, vertical and horizontal control joints may be necessary to accommodate movement and prevent cracking.
- Mortar Type: The specific type of mortar (e.g., Type S, N, M) will depend on local building codes, climate, and the specific veneer product being used. Always refer to the stone veneer manufacturer's guidelines.
Understanding these layers ensures a durable and aesthetically pleasing stone veneer installation that will stand the test of time.
