Written by Stucco Champions — Southern California’s Authority on Exterior Plastering.
The Architectural Edge: A Technical Guide to Stucco Quoins
In classical architecture, "Quoins" (pronounced coins) were large, structural stones placed at the corners of brick buildings to provide strength. In modern Southern California stucco design, they are purely aesthetic, but they serve a vital visual function: they frame the home, adding weight, elegance, and definition to what would otherwise be a plain box.
Whether you are designing a French Country estate in Newport Coast or updating a Mediterranean home in Mission Viejo, understanding the material composition of modern quoins—specifically the shift from metal to EPS foam—is critical for a long-lasting installation.
1. The Evolution: Foam vs. Metal
Historically, stucco quoins were built by furring out the wall with extra layers of wire lath and cement. Today, technology has evolved.
The Modern Standard: EPS Foam
95% of new quoins installed in SoCal are made from Expanded Polystyrene (EPS) foam (1lb or 1.5lb density).
Why?
1. Seismic Flexibility: Foam absorbs vibration. Heavy cement quoins often crack during micro-tremors; foam moves with the house.
2. Insulation: It eliminates thermal bridging at the corners.
3. Cost: It creates complex shapes without expensive wood framing.
The "Old School": Wire Lath
We still occasionally build traditional quoins using built-up wire mesh (High-Rib Lath) and solid cement. This is primarily done in high-impact zones (like the base of a commercial building) where foam might get dented by vehicles.
2. Construction of a Foam Quoin
A quality quoin isn't just a piece of Styrofoam glued to the wall. It is a composite system.
- The Core: CNC-cut EPS foam.
- The Armor: A layer of fiberglass mesh embedded in a polymer-modified base coat. This creates a hard, impact-resistant shell.
- The Finish: An acrylic or cement finish coat that matches the texture of the main house.
3. Installation Protocols
How we attach the quoin determines if it stays on the wall.
We do not use nails or screws, which create water entry points. We use a polymer-modified adhesive mortar (like Foam-Tek or Primus). This glue creates a chemical bond between the brown coat of the wall and the back of the foam, stronger than the foam itself.
4. Design Profiles: Staggered vs. Stacked
The layout of the quoins dictates the architectural style:
- The "Gibbs" Surround (Staggered): Alternating long and short blocks. This mimics traditional English or Georgian masonry and breaks up the vertical line.
- The Stacked Column: Uniform square blocks stacked vertically. This creates a formal, modern, or Art Deco appearance.
- Chamfered Edges: We often bevel the edges of the foam to create shadow lines, making the "stone" look realistic rather than just a flat block.
5. The Water Management Warning
Adding foam to a wall changes how water flows.
A critical failure we see in DIY installations is running the quoin all the way down to the dirt/pavement.
The Rule: The quoin must terminate above the Weep Screed. If you glue foam over the weep screed, you trap moisture inside the wall, leading to mold and rot. We maintain a 2-inch clearance from the paving.
6. Customization
Because we use laser-cut foam, the design possibilities are endless. We can create arched quoins, battered (sloped) quoins, or rusticated (rough-textured) looks.
Note on Sourcing: We partner with specialized fabricators like New Image Foam to cut custom profiles to your architect's exact CAD specifications.
Conclusion: Architectural Jewelry
Quoins are the "finishing touch" that elevates a stucco exterior from standard to custom. By using modern EPS foam systems installed with proper drainage clearance, Stucco Champions ensures these details add value and beauty without compromising the waterproofing envelope.
Last week, we shared Guide For Stucco Application in Rainfall. If you are scheduling exterior upgrades during winter, this is essential reading.
