Concrete might look dry on the surface — but what’s happening inside the slab can determine whether your coating succeeds or fails.
Moisture-related failures are one of the most common causes of peeling, blistering, and delamination in epoxy and resinous flooring systems. The culprit? Excess moisture vapor trapped beneath the coating.
Skipping moisture testing can turn a profitable job into an expensive redo.
Why Moisture Matters
Concrete is porous and continues to transmit moisture vapor long after it cures. When coatings are applied over slabs with high internal moisture:
- Vapor pressure builds
- Adhesion weakens
- Bubbling and blistering occur
- Coatings delaminate
The result: costly removal, re-prep, new materials, and lost time.
Common Moisture Testing Methods
In-Situ Relative Humidity (RH) Testing
Measures internal slab moisture (ASTM F2170).
Often preferred by manufacturers because it reflects long-term moisture conditions.
Calcium Chloride Testing (MVER)
Measures surface vapor emission rate (ASTM F1869).
Useful, but only evaluates the top portion of the slab.
Moisture Meters
Great for quick scanning and identifying trouble areas — but not a replacement for ASTM-compliant testing.
When Should You Test?
- Before any epoxy or resinous coating application
- On new slabs (even if fully cured)
- After water exposure
- On below-grade or unknown vapor barrier slabs
Even older concrete can retain and transmit moisture.
Protect Your Warranty — and Your Margins
Most coating manufacturers specify maximum RH or MVER limits. Exceeding those limits can void warranties and lead to failure.
Testing takes a few extra hours. Replacing a failed floor takes days — and thousands of dollars.
Moisture testing isn’t optional — it’s part of professional surface prep.
Know your numbers before you coat. It protects your profit, your reputation, and your customer!
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