Understanding Under-Slab Vapor Barriers
Whether it is evident on the surface, water exists, to some degree underneath a building. This water can migrate through the soil and potentially contact the bottom of a concrete slab. A layer of free draining crushed fill between the sub-grade and the slab is typically installed to restrict the capillary rise of water; however, this will not prevent water vapor from reaching the concrete. For this you’ll need a high performance under-slab vapor barrier between the sub-base material and slab.
VAPOR BARRIER BACKGROUND
Water vapor from sub-slab conditions will pass through the pores of an unprotected concrete slab through vapor diffusion. This vapor transmission creates a conflicted environment for the floor coating or adhesive. Because government regulations were established to reduce volatile organic compounds (VOCs) found in numerous architectural coatings, specifically floor coatings and adhesives, many solvent based flooring materials have been changed to water based. When exposed to water and alkalinity, these water based coatings and adhesives are prone to re-emulsification resulting in costly flooring failures. In addition to flooring failures, moisture migration also creates poor indoor air quality (IAQ), mold, mildew, fungi and damage to the slab and its components.
VAPOR BARRIER PURPOSE
The infiltration of water vapor and gas from the earth through concrete slabs is a costly building liability. Under-slab vapor barriers/retarders provide an inexpensive insurance policy to protect floors and other moisture sensitive equipment within the building’s interior. The definition of a vapor barrier/retarder, according to ASTM E1745, “is a material or construction that impedes the transmission of water vapor under specified conditions.” By inhibiting moisture and soil gas migration, under-slab vapor barriers/retarders greatly reduce condensation, retard mold growth, provide healthy breathing conditions within a building, prevent flooring failures and aid in controlling structural degradation.
WHAT TO LOOK FOR IN A VAPOR BARRIER
ASTM E 1745 (Standard Specification for Plastic Water Vapor Retarders Used in Contact with Soil or Granular Fill under Concrete Slabs) standardizes vapor barriers/retarders according to various performance properties. The three classes (A = highest, B = middle, C = lowest) are based on a membranes resistance to punctures, tears and water vapor. When choosing under-slab vapor barriers/retarders, it is important to look for products that are independently tested and exceed all ASTM E1745 requirements. Furthermore, vapor barrier/retarder products should be made from virgin (non-recycled) resin to assure long term protection.
THE SOLUTION
Viper II is the first line of defense against all damaging water vapor and soil gas threats existing below the concrete slab. Viper II is a multi-layer, extruded, virgin polyolefin under-slab vapor barrier/retarder. The virgin resin used to manufacture Viper II contributes to it’s long term stability and prevents the material from breaking down when buried below the slab. Viper II is engineered with superior resistance against punctures, tears and water vapor. The high puncture resistance and tensile strength greatly reduce potential damage when exposed to rigorous job site conditions. Furthermore, VIPER II products have very low water vapor permeance properties which are key to preventing water vapor migration.