Over 16 years of field experience, we’ve seen the same installation mistakes repeated across hundreds of projects. The good news: these mistakes are entirely preventable. This guide compiles the best practices that separate successful installations from those that fail within a few years.
Mistake #1: Inadequate Substrate Preparation
This is the most common — and most consequential — error. Metal lath installed over a dirty, unstable, or unsuitable substrate will not perform properly regardless of how well the lath itself is installed.
Best practices:
- Remove all loose material, dust, oil, and form release agents from concrete or masonry substrates.
- On wood sheathing, verify that the sheathing is properly fastened to studs and free from water damage or delamination.
- On existing structures, repair deteriorated substrates before installing lath.
- Apply appropriate primers or bonding agents where specified.
Mistake #2: Insufficient Lap Joints
The second most common error is reducing lap dimensions below code requirements. It’s tempting to reduce laps to save material, but the consequence is concentrated stress at sheet edges — exactly where cracks start.
Best practices:
- Side laps: Minimum 2″ (50mm), fastened at 6″ (150mm) on center along the lap.
- End laps: Minimum 1″ (25mm), fastened at 6″ (150mm) on center across the lap.
- Never reduce lap dimensions without written approval from the project’s structural engineer or architect.
Mistake #3: Wrong Fasteners or Fastening Schedule
Using incorrect fasteners or incorrect spacing compromises the entire system. The fasteners are what transfer loads from the lath and plaster to the structural substrate.
Best practices:
- Use corrosion-resistant fasteners (hot-dip galvanized or stainless steel) — never bright steel fasteners.
- Fastening schedule: 6″ (150mm) on center at supports (studs, joists, furring channels).
- For ceiling applications, additional fastening at 7″ (175mm) on center at intermediate supports.
- Drive fasteners flush — not countersunk. Countersunk fasteners tear the lath and reduce holding power.
Mistake #4: Running Lath Through Control Joints
Control joints are designed to concentrate cracking at predetermined locations. Running continuous lath through a control joint defeats this purpose and guarantees cracking elsewhere.
Best practices:
- Cut the lath at every control joint location.
- Leave a minimum 3/8″ (10mm) gap between lath edges at control joints.
- Install control joints in strict accordance with the project’s crack control plan.
Mistake #5: Neglecting Corner Reinforcement
External corners are high-stress, high-impact areas. Without proper reinforcement, corners chip, crack, and deteriorate rapidly.
Best practices:
- Install corner bead or corner reinforcement at all external corners.
- Use metal corner bead with a minimum 1-1/4″ (32mm) flange on each side.
- Fasten corner bead at 6″ (150mm) on center on each flange.
- For high-impact areas (schools, commercial buildings), consider reinforced corner guards.
Mistake #6: Improper Lath Orientation
Lath has a correct orientation. Installing it upside down reduces plaster keying and can lead to sagging in ceiling applications.
Best practices:
- Install lath with the long axis of the diamond pointing upward (toward the ceiling).
- This orientation allows plaster to key in from below and provides maximum resistance to plaster sag.
- If the lath has a paper backing, install with the paper toward the substrate.
Installation Checklist
Before applying plaster, verify:
- Substrate is clean, stable, and properly prepared.
- Lath weight, mesh size, and galvanization meet specifications.
- All lap joints are minimum 2″ side lap, 1″ end lap, and properly fastened.
- Fastener spacing is correct (6″ on center at supports).
- Lath is cut at all control joint locations.
- Corner reinforcement is installed at all external corners.
- Lath orientation is correct (long axis of diamonds pointing upward).
Conclusion
Successful lath installation is not complicated, but it requires attention to detail. The six mistakes described here account for the vast majority of installation failures. By following the best practices outlined in this guide and using the installation checklist, you can ensure that your plaster or stucco system performs as designed for decades.