What is a Vapor Barrier? (Keeping Moisture Out)

What is a Vapor Barrier? (Keeping Moisture Out)

A vapor barrier is plastic sheeting placed under the slab. It prevents ground moisture from rising up through the concrete and delaminating epoxy floors or causing other moisture problems later. Understanding vapor barriers helps ensure your concrete installation protects against moisture issues.

What is a Vapor Barrier?

A vapor barrier is:

• Plastic sheeting: Typically 6-10 mil polyethylene
• Placed under slab: Installed on base before concrete
• Moisture barrier: Prevents moisture migration
• Protective layer: Protects concrete and finishes

How It Works

The vapor barrier blocks moisture:

1. Ground moisture: Soil contains moisture
2. Moisture tries to rise: Water vapor moves upward
3. Barrier blocks it: Plastic prevents moisture from passing through
4. Keeps concrete dry: Concrete stays dry from below

Why It Matters

Ground moisture can cause problems:

1. Epoxy Floor Delamination

• Moisture rises: Ground moisture travels up through concrete
• Reaches epoxy: Moisture reaches epoxy coating
• Breaks bond: Moisture breaks bond between epoxy and concrete
• Delamination: Epoxy peels off

2. Other Moisture Problems

• Moisture-sensitive finishes: Other coatings may fail
• Mold growth: Excess moisture can cause mold
• Floor covering issues: Moisture can damage floor coverings

When Vapor Barriers Are Essential

Vapor barriers are essential:

• Epoxy floors: Required for epoxy coatings
• Moisture-sensitive finishes: Any finish sensitive to moisture
• Ground contact: Slabs in direct contact with ground
• High water table: Areas with high groundwater

Installation

Proper installation is critical:

1. Prepare base: Level and compact base
2. Lay plastic: Cover entire area
3. Overlap seams: Overlap sections by 6-12 inches
4. Seal seams: Tape seams for complete coverage
5. Protect from damage: Don't puncture during installation

The Bottom Line

A vapor barrier is plastic sheeting placed under the slab that prevents ground moisture from rising up and delaminating epoxy floors or causing other moisture problems. It's essential for epoxy floors and moisture-sensitive finishes. Without a vapor barrier, ground moisture can travel up through concrete, breaking bonds and causing failures. Always install a proper vapor barrier when moisture protection is needed.

Need help with vapor barrier installation? Contact Local Concrete Contractor. We install vapor barriers properly to protect your concrete and finishes from moisture problems.