Driveway Vapor Barrier: When to Use Plastic Sheeting

What Is a Driveway Vapor Barrier?

A driveway vapor barrier is a continuous sheet of heavy-duty plastic that blocks moisture from moving up or down through the sub-base and into the concrete or asphalt above. Think of it as a one-way raincoat: it keeps ground water from wicking upward while still allowing any trapped construction water to evaporate out the top surface.

Homeowners often confuse vapor barriers with weed fabric or standard 1-mil painter’s plastic. True driveway-grade vapor retarders are 6–15 mil thick, meet ASTM E1745 Class A, B, or C standards, and are installed before any concrete pour or paver base.

Why Your Driveway Might Need a Vapor Barrier

Water is concrete’s silent enemy. When vapor moves through a slab it can:

• Push salts to the surface (efflorescence)
• Trigger freeze-thaw spalling in northern climates
• Cause decorative coatings to bubble or delaminate
• Support mold and mildew in attached garages

Installing a vapor barrier cuts these risks and is cheap insurance compared with resurfacing later.

Climate Zones That Benefit Most

• High water table areas (coastal Florida, Gulf Coast, parts of the Pacific Northwest)
• Heavy clay soils that hold moisture (Dallas–Fort Worth, Atlanta, Denver expansives)
• Cold regions subject to de-icing salts (Upper Midwest, New England)

Site Red Flags

1. Standing water after rain
2. White mineral stains on existing concrete
3. Musty odors inside an adjacent basement or garage
4. Previous slab heaved or cracked in first five years

Vapor Barrier vs. Vapor Retarder: Does the Name Matter?

Technically, a barrier must have a permeance rating of 0.01 perms or less (ASTM E1745 Class A). A retarder can allow up to 0.1 perms. For residential driveways the terms are used interchangeably, but insist on 6-mil or thicker polyethylene that meets at least Class C. Anything thinner is landscape plastic and will tear under 4 inches of concrete plus steel reinforcement.

How to Install Plastic Sheeting Under a New Driveway

If your contractor says “We always pour right on gravel,” show them these steps.

Step 1: Grade & Compact Sub-grade

Excavate to the depth required by local code—usually 7–9 in. for passenger cars, 10–12 in. for RV pads. Compact soil to 95 % Modified Proctor density to avoid future settlement that could rip the plastic.

Step 2: Choose the Right Mil & Sheet Width

• 6-mil: absolute minimum; okay for temperate, well-drained sites
• 10-mil: best value for most homes
• 15-mil: go-to for high water table, heated slabs, or when a warranty is required

Use 12-ft-wide rolls to minimize seams. Overlap joints 6 in. and seal with vapor-barrier tape (not duct tape).

Step 3: Add Base Layer

Place 4 in. of crushed limestone or recycled concrete aggregate (RCA) directly on top of the plastic. The stone protects the sheet from punctures during the pour and provides capillary break.

Step 4> Pour Concrete or Lay Pavers

Keep concrete trucks on the street the first day; driving heavy wheelbarrows over uncovered plastic can tear it. If you see holes, patch with vapor-barrier tape before the concrete trucks arrive.

Can You Retrofit a Vapor Barrier to an Existing Driveway?

Short answer: not really. To be effective, the sheet must run continuously under the entire slab. Options instead:

• Topical sealers: Silane-siloxane sealers reduce surface absorption and slow vapor but do not stop soil moisture.
• Slab replacement: If your driveway is already spalling or has widespread D-cracking, budget for removal and new pour with proper barrier.
• Overlay with moisture-mitigating primer: Epoxy primers rated for 3-lb/1000 ft²/24 h moisture vapor emission can be used before stamped overlay. Cost is $2–$3 per square foot on top of overlay price.

Best Plastic Sheeting Products for Driveways

Big-box 6-mil “contractor” plastic is okay for short-term curing blankets, not for long-term moisture control. Buy from a concrete supply house or online industrial retailer. Look for:

• ASTM E1745 listing printed on the roll
• UV resistance if the project might sit exposed for weeks
• Color: clear lets you see tears; black hides stains but gets hot—either works

Recommended brands: StegoWrap, Griffolyn, Raven Industries Dura-Skrim, and Americover VaporBlock. Expect to pay $0.07–$0.15 per square foot for 10-mil.

Cost Breakdown: DIY vs. Contractor

Material for a 20 × 40 ft (800 ft²) driveway:

• 10-mil vapor barrier: 1,000 ft² roll = $90
• Barrier tape (2 rolls) = $24
• Delivery = $35
• Total DIY material: ≈ $150

Contractors typically mark up 20 % and include it in the full concrete package. On a $7,500 driveway, adding a vapor barrier adds only about $180—less than 2.5 %. Always request it as a line item so you can verify thickness on delivery.

Common Mistakes Homeowners Make

• Skimping on thickness: 4-mil painter’s plastic disintegrates under aggregate.
• Skipping tape at seams: A 1/8-in. gap lets through 100× more moisture.
• Walking on plastic in windy conditions: One boot tear can funnel water into a channel.
• Placing plastic on top of base instead of under: Stone punctures the sheet when you compact.

Environmental & Warranty Considerations

Polyethylene is recyclable. Ask your supplier if they participate in a take-back program. From a warranty standpoint, many decorative coating manufacturers (BEHR, SherCrete, Eagle) void their warranty if moisture vapor emission exceeds 3 lb/1000 ft²/24 h. A vapor barrier installed at pour time is the easiest way to stay under that limit for the life of the slab.

Frequently Asked Questions