Concrete 101: Moisture Vapor Emission & Vapor Barriers in Slabs

Concrete might look solid, but it’s actually porous. That means water vapor can move through it — and in some cases, this leads to big problems like flooring failures, mold, or damp basements. This process is called moisture vapor emission (MVE).

What is Moisture Vapor Emission?

MVE is the movement of water vapor from the ground or within the concrete up to the surface.
Even slabs that “look dry” may still be releasing moisture.
Flooring like hardwood, tile, or vinyl can fail if the vapor pressure isn’t managed properly.

Controlling Moisture in Slabs

Vapor Barriers/Membranes: Placed under the slab before the pour to block vapor from the soil.
Proper Curing: Ensures concrete dries evenly and reduces excess trapped moisture.
Moisture Testing: Tools like RH probes or calcium chloride tests measure MVE before flooring is installed.
Sealants & Coatings: Can provide extra protection on the slab surface when needed.

Why It Matters

Moisture issues may not show up right away — but without proper planning, they can cause costly repairs later. By understanding vapor movement, contractors and homeowners can keep slabs dry, safe, and long-lasting.

👉 A solid slab starts with more than just concrete — it starts with protection from below.

⚠️ Legal Disclaimer:
This blog post is intended for informational purposes only and should not be taken as professional, legal, or construction advice. Every project is unique, and conditions may vary. RLW Concrete LLC is not liable for any actions taken based on this information. Always consult with a qualified professional or attorney for your specific needs.
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