Written by Stucco Champions — Southern California’s Authority on Exterior Plastering.
What Is One-Coat Stucco? An In-Depth Guide to Energy Efficiency
The name "One-Coat Stucco" is one of the most confusing terms in the construction industry. It implies a single layer of material. In reality, it is a sophisticated, multi-layered assembly designed to meet California's strict Title 24 energy codes.
Unlike the traditional "Three-Coat" system which relies on mass (thick cement) for strength, the One-Coat system relies on engineering (fiber-reinforced cement + foam insulation). This guide breaks down the anatomy of the system that dominates modern tract home construction.
1. The Anatomy of the System
A "One-Coat" system is actually three distinct layers applied over the framing. It gets its name because the grey cement base is applied in a single pass (3/8" to 1/2") rather than two separate passes (Scratch and Brown).
Layer 1: The Insulated Lath (R-Value)
This is the game changer. Instead of just wire paper, we install 1-inch rigid EPS Foam Board over the studs.
The Benefit: This provides "Continuous Insulation," breaking the thermal bridge of the wood studs and keeping your home cooler in summer.
The Wire: A 20-gauge wire mesh is attached to the face of the foam to hold the cement.
Layer 2: The Fiber-Reinforced Base Coat
This is the "One Coat." We apply a specialized cement mix (like Omega or Quikrete One-Coat) that contains chopped fiberglass strands.
Why Fibers? Because this layer is thinner than traditional stucco (3/8" vs 7/8"), the fiberglass acts as internal reinforcement to prevent cracking and add flexural strength.
Layer 3: The Finish Coat
Just like traditional stucco, the final layer is a decorative texture (1/8" thick). It can be a cement-based "Old World" finish or a modern Acrylic finish.
2. One-Coat vs. Three-Coat: Which is Better?
Homeowners often ask: "Is One-Coat cheaper/worse than Three-Coat?"
It isn't worse; it's different.
- Three-Coat (Traditional): Best for impact resistance (solid rock) and fire rating (1-hour). Preferred for custom estates.
- One-Coat (Modern): Best for energy efficiency (insulation) and speed of construction. Preferred for production homes and retrofits.
3. Application: Speed & Efficiency
The major advantage for builders is speed.
In a traditional system, you must wait 48 hours between the scratch and brown coats. In a One-Coat system, the base coat is applied in a single day. It typically cures for 7 days before the finish is applied, cutting the schedule in half.
Because the cement shell is thinner (approx 1/2" total), One-Coat stucco is easier to puncture. A heavy impact (like a baseball or car bumper) can punch through the cement and crush the foam behind it. Repairs on foam systems are more complex than solid cement repairs.
Conclusion: Efficiency vs. Mass
If your priority is lowering your AC bill and meeting modern energy codes, One-Coat Stucco is the superior choice. If your priority is a bulletproof wall that can take a beating, stick with Traditional Three-Coat. Both are excellent systems when installed to ASTM standards.
Last week, we shared What Is Stucco Lath?. The wire used for One-Coat is different from Three-Coat—learn why.