A concrete vapor barrier is an essential part of moisture control on any jobsite where slabs are poured. If you’re placing concrete directly over soil or aggregate without a proper barrier, you’re leaving the slab vulnerable to water infiltration, mold growth, adhesive failures, and long-term structural damage.
At Americover, we help contractors tackle moisture intrusion with durable concrete vapor barriers and drainage solutions like Enka® products to manage hydrostatic pressure around slabs and foundations.
Here’s what you need to know to protect your next build.
What Is A Concrete Vapor Barrier?
A concrete vapor barrier is a tough plastic membrane that gets installed directly beneath a concrete slab to block moisture migration from the ground. It’s your first line of defense against water vapor entering the slab and causing downstream issues like flooring failures or slab curling.
Minimum Thickness Recommendation
According to ACI 302.2R-06, a vapor barrier used under concrete slabs in direct contact with soil should be a minimum of 10 mils, though 15 to 20 mils is preferred for enhanced durability, puncture resistance, and long-term performance.
(Source:Concrete.org)
Contractors often make the mistake of treating a vapor barrier like it’s the same as what’s used in bathroom walls or behind drywall—but these products serve very different purposes. A standard 6 mil construction-grade poly may be acceptable for interior use, but it does not meet the performance requirements for placement beneath a concrete slab.
Here’s why 6 mil poly falls short:
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It typically has low tensile strength, making it prone to tearing during installation.
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It can be damaged easily by subgrade irregularities like rocks or debris.
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Most critically, its permeance rating is too high to effectively block water vapor migration from the soil.
A proper concrete vapor barrier must withstand:
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Abrasion and tension during installation,
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Shifting and settling of the ground below,
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And the weight of freshly poured concrete without puncturing or degrading.
That’s why high tensile strength and low perm ratings (≤0.01 perms) are essential. Going with a thin or generic plastic sheet might save money upfront, but it can lead to moisture intrusion, flooring failures, and expensive slab repairs later on.
Why Are Concrete Vapor Barriers Important?
When installed properly, a concrete vapor barrier helps maintain the structural integrity of slabs by preventing both liquid and vapor moisture from moving upward into the concrete. This protects adhesives, flooring systems, insulation, and other materials from deterioration.
What Happens Without One?
- Moisture enters the slab, condenses under the flooring, and leads to warping, bubbling, and adhesive breakdown.
- Efflorescence and mold can form, especially in conditioned spaces like basements.
- Slab curling and cracking occur when moisture causes uneven drying or swelling in the concrete.
A concrete vapor barrier is your insurance policy against these expensive and time-consuming repairs.
For added protection in areas with poor drainage, pairing a vapor barrier with Enka® drainage mats can direct water away from the structure and prevent long-term moisture buildup.
Related Article: Crawl Space Waterproofing 101
Combatting Subsurface Water: Hydrostatic Pressure
Subsurface water movement isn’t just a nuisance—it creates hydrostatic pressure that can force moisture through cracks, joints, and porous concrete.
When you’re building near high water tables or in areas with heavy clay content, drainage solutions become just as important as vapor barriers.
How Enka® Products Help Relieve Hydrostatic Pressure
Americover’s Enkadrain® is designed to alleviate pressure from groundwater. It’s made with a high-strength polymer core sandwiched between geotextile fabrics that allow water to flow freely while keeping soil and debris out.
Key Benefits for Contractors:
- Supports vertical or horizontal applications
- Works behind retaining walls, under slabs, or along foundation walls
- Reduces build-up of water that causes slab failures or basement leaks
When combined with a concrete vapor barrier, Enkadrain ensures comprehensive moisture management from the ground up.
Related Article: Crawl Space Waterproofing Essentials for Contractors: Vapor Barriers vs. Drainage Mats
Protecting Against Soil Gases Like Radon
Moisture isn’t the only threat rising from the soil—soil gases like radon pose a serious health risk, especially in residential and commercial foundations built on or near bedrock or high-radon zones. Radon is a naturally occurring radioactive gas that can seep through cracks and concrete pores into enclosed structures. Long-term exposure is the second leading cause of lung cancer in the U.S., according to the EPA.
While many concrete vapor barriers block moisture, very few are engineered to stop gas transmission at a molecular level.
The Ultimate Solution: VaporBlock® Plus 20
For high-performance radon mitigation, VaporBlock® Plus 20 is the only barrier we recommend—it features a seven-layer co-extruded construction with an EVOH (ethylene vinyl alcohol) core, which acts as a powerful gas barrier.
Why EVOH Matters:
- EVOH is virtually impermeable to gas molecules like radon, methane, and VOCs (volatile organic compounds).
- It outperforms traditional polyethylene barriers in both moisture and gas resistance.
- The multi-layer structure enhances durability while maintaining flexibility and puncture resistance.
If your project is in an area known for radon or requires compliance with environmental or health standards, VaporBlock® Plus 20 is the professional-grade solution that delivers peace of mind and long-term protection.
The Moisture Prevention Products You Need
Americover stocks jobsite-ready solutions that meet the needs of commercial, industrial, and residential contractors:
- Enkadrain® – Lightweight drainage mat that manages hydrostatic pressure around slabs and foundations.
- Pro Crawl Barrier – A Class A, 10 mil concrete vapor barrier with high tensile strength and low perm rating. This barrier exceeds ASTM E1745 Class A standards and stands up to demanding soil conditions.
Get Your Concrete Vapor Barrier And Drainage Products Today
With over 30 years of experience supplying specialty plastic sheeting, Americover is your go-to source for high-quality concrete vapor barriers and drainage systems. Whether you’re pouring a slab on grade, encapsulating a crawl space, or waterproofing a foundation, we have the products and expertise to help you get it done right.
Call 760-388-6294 or contact us to request a quote.