Written by Stucco Champions — Southern California’s Authority on Exterior Plastering.
Should You Replace Rusty Weep Screed? A Technical Assessment
In the coastal and high-humidity zones of Southern California, rust at the foundation line is a common sight. This corrosion attacks the Weep Screed, the critical metal flashing responsible for draining moisture from your stucco walls. While unsightly, rust is often ignored until it causes significant structural damage.
So, when does "surface rust" become "structural failure"? This guide explains the pathology of metal corrosion in stucco systems and the professional protocol for repair.
1. The "Rust Jacking" Phenomenon
Weep screeds are typically made of galvanized steel (zinc-coated). Over time, moisture and soil acidity eat through the zinc, exposing the raw steel to oxygen.
What Happens Next: Iron oxide (rust) occupies 4-6 times the volume of the original steel. As the metal rusts, it expands. This force, known as "Rust Jacking," cracks the surrounding stucco and pushes it off the wall, creating a direct path for water and termites to enter the framing.
2. Diagnostic Matrix: Monitor vs. Replace
Not every rust stain requires demolition. Use this guide to assess severity.
| Symptom | Diagnosis | Action Required |
|---|---|---|
| Orange Stains Only | Cosmetic Surface Rust. | Wire brush, prime with rust inhibitor, and paint. |
| Flaking Metal | Pitting Corrosion. The metal is thinning. | Monitor closely; plan for replacement in 1-2 years. |
| Cracked Stucco | Rust Jacking. The metal is expanding. | Immediate Replacement. The envelope is compromised. |
| Perforation (Holes) | Total Failure. Water is entering the wall. | Emergency Replacement to prevent dry rot. |
3. The Replacement Protocol
Replacing a weep screed is a surgical procedure. You cannot just slide a new one in.
- Demolition: We saw-cut the bottom 8-12 inches of stucco along the entire affected wall to expose the framing.
- Extraction: The old, rusted screed is pried off. We inspect the mudsill plate (wood framing) for rot and termites.
- Integration: A new screed is installed. Critical Step: New waterproof paper must be slid under the existing paper above to create a shingle lap.
- Re-Stucco: We install new wire lath and apply a three-coat patch to match the existing texture.
4. Upgrade Options: Vinyl & Stainless
If you live near the beach (Salt Air Zone), replacing galvanized with galvanized is a temporary fix. It will rust again.
The Upgrade:
- Vinyl (PVC) Screed: Impervious to rust. The best choice for coastal homes, though less rigid than metal.
- Stainless Steel: Extremely expensive but virtually indestructible. Used in high-end custom estates.
The #1 cause of premature rust is Soil Contact.
Code requires a 4-inch clearance between the weep screed and the earth. If you pile mulch or dirt against the metal, the acidity in the soil eats the galvanization in months. Keep the grade low!
Conclusion: Don't Wait for the Leak
A rusty weep screed is a "Check Engine Light" for your home. Catching it early allows for a simple repair. Ignoring it leads to dry rot repairs costing thousands. At Stucco Champions, we specialize in the surgical replacement of these critical components, ensuring your home's drainage system functions perfectly.
Last week, we shared What Is a Weep Screed? Understand the physics of drainage.