Written by Stucco Champions — Southern California’s Authority on Exterior Plastering.

Applying Stucco to Metal Buildings: An Expert Guide to Load & Deflection

Metal buildings—whether prefab sheds, workshops, or commercial steel structures—are prized for durability but often criticized for their industrial appearance. The most common question we get is: "Can I stucco over this metal siding to make it look like my house?"

The short answer is Yes. However, treating a metal building like a wood-framed house is a recipe for disaster. Metal expands in heat, vibrates in wind, and has different load-bearing capacities. This guide explains the engineering required to make the bond last.

1. The Weight Problem: 12 lbs vs. 6 lbs

Before applying a single trowel of cement, you must determine if your metal frame can hold the weight.

• Traditional 3-Coat Stucco: Weighs approximately 10-12 lbs per square foot. Most lightweight prefab sheds cannot support this load without buckling.
• One-Coat / Foam System: Weighs approximately 4-6 lbs per square foot. This is the preferred method for metal structures.

2. The Insulation Solution (R-Value)

Metal transfers heat instantly. Without insulation, a stuccoed metal building will be an oven in summer and a freezer in winter.
The Fix: We install 1-inch or 1.5-inch EPS Foam Board over the metal skin before lathing.
This serves two purposes:
1. Insulation: It creates a thermal break, drastically improving energy efficiency.
2. Isolation: It separates the rigid stucco from the expanding/contracting metal skin, preventing thermal cracking.

3. Fastening: Self-Tapping Screws

You cannot use nails on a metal building. You must use Self-Tapping Ceramic Coated Screws with washers.

The Protocol:
1. Attach the foam board through the metal ribs into the structural purlins (studs) using heavy-gauge screws.
2. Install the wire lath through the foam, ensuring the fasteners bite into the steel frame, not just the thin metal siding.

4. Deflection: Why Metal Cracks Stucco

Metal walls flex (deflect) in the wind more than wood walls. If you apply brittle cement over a flexing wall, it will crack.

5. The Application Process

Once the engineering is solved, the application follows a specific sequence:

• Layer 1: Tyvek StuccoWrap or Grade D Paper (to prevent galvanic corrosion between the steel building and the wire lath).
• Layer 2: EPS Foam Board (optional but recommended).
• Layer 3: Self-Furred Wire Lath screwed into structural members.
• Layer 4: Fiber-Reinforced Base Coat (adds strength).
• Layer 5: Acrylic Finish Coat.

Conclusion: It’s an Engineering Project

Stuccoing a metal building turns a utility structure into a permanent architectural feature. However, it requires respecting the weight limits and thermal movement of steel. By using a lightweight foam system and acrylic finish, Stucco Champions ensures your metal building looks like a custom home.