Written by Stucco Champions — Southern California’s Authority on Exterior Plastering.
Don't Skip This Step: Lath Installation Can Make or Break Your Stucco
When homeowners think about stucco, they focus on the finish texture and the color. But the longevity of your exterior is determined long before the first bucket of cement is mixed. It is determined by the Lath—the hidden assembly of paper and wire that anchors the system to your home.
Lathing is the skeleton of your stucco. If the lath is loose, the wall will sag. If the paper is lapped incorrectly, the studs will rot. This guide explains the technical components of a code-compliant lath system and why it is the foundation of long-lasting stucco.
1. The Anatomy of Lath
Lathing is not just stapling chicken wire to a wall. According to ASTM C1063, a proper lathing assembly consists of three distinct layers working together:
- The Drainage Plane (Waterproofing): Two layers of Grade D building paper (Super Jumbo Tex). This separates the wet stucco from the dry wood framing.
- The Reinforcement (Wire): Galvanized metal mesh that holds the cement.
- The Accessories (Flashings): Weep screeds, casing beads, and corner aids that define the edges and drainage points.
2. The Two-Layer Waterproofing Rule
In Southern California, we face intense "wet-dry" cycles. This makes the waterproofing layer critical.
Code requires two separate layers of paper over plywood sheathing.
Layer 1: The "Sacrificial Layer." It bonds to the stucco and absorbs moisture.
Layer 2: The "Barrier Layer." It remains separate from the stucco, creating a tiny air gap (drainage plane) that allows water to run down to the weep screed instead of soaking into the wood.
3. Fastening: Shear Strength and Seismic Safety
Stucco is heavy (10-12 lbs per sq. ft.). The fasteners holding the lath must support this weight plus the lateral forces of an earthquake.
- Stud Spacing: Staples must be driven into the studs, typically every 6 inches vertically.
- Furring: We use "Self-Furring" wire. This wire has small crimps that hold the mesh 1/4 inch away from the wall. This allows the scratch coat to flow behind the wire, fully embedding it in cement. If you use flat wire, the cement won't key in, and the wall will fail.
4. Common Mistakes We Avoid
Why do some stucco jobs crack in 6 months? Usually, it's a lathing error.
- Improper Lapping: Wire mesh must overlap by at least 1 inch horizontally and 2 inches vertically. If the wire isn't continuous, the stucco will crack in a straight line at the seam.
- Missing Weep Screeds: If the lath runs into the dirt without a weep screed, moisture wicks up the wall (capillary action), rotting the mudsill.
- Reverse Lapping: Installing paper from top-to-bottom instead of bottom-to-top. This traps water behind the paper rather than shedding it.
Conclusion: Inspect the Bones
Before the brown coat covers everything up, the lath installation is your only chance to verify quality. A tight, properly lapped lath system ensures your home is waterproof, fire-resistant, and structurally sound for decades. At Stucco Champions, we treat the lath inspection as the most critical phase of the project.
Last week, we shared The Comprehensive Guide to Stucco Lathing Wire Types. Learn which wire gauge is right for your project.