ASTM E1745
Standard Specification for Plastic Water Vapor Retarders Used in Contact with Soil or Granular Fill under Concrete Slabs
The plastic sheeting installed under a slab on grade to block moisture vapor rising out of the ground, and the Class A, B, and C designations that rank its toughness.
Who needs it
Slab contractors, flooring installers, building envelope designers, and anyone specifying a slab that will receive moisture-sensitive floor covering.
What the test involves
It sets requirements for water vapor permeance, tensile strength, and puncture resistance, with the three classes representing progressively tougher material for progressively rougher installation conditions. The permeance requirement is what makes a product a vapor retarder rather than merely a plastic sheet; the strength requirements are what keep it intact after crews walk on it and set rebar over it. Installation details such as lapping and sealing penetrations are addressed in companion documents rather than here.
Common misconceptions
- Hardware-store polyethylene sheeting is not an equivalent product. It is not qualified for permeance and it typically will not survive installation intact.
- Class A, B, and C describe physical toughness for the installation environment, not moisture performance tiers — the permeance requirement applies across the classes.
- A vapor retarder torn during rebar placement or left unsealed at pipe penetrations provides far less protection than the rating suggests, and flooring failures are frequently traced to exactly that.
Official source
We summarize scope and purpose only. The full text belongs to the issuing body — read it at the official source. ASTM International