Prevent Moisture Migration with Underslab Vapor Barriers
Underslab vapor barriers — also called a moisture barrier for concrete — are an effective way to prevent moisture migration. When this plastic sheeting is installed beneath concrete, it eliminates the risk of fungus, mildew, and mold from developing over time.
To protect your projects and adhere to code specifications, it’s important to select the highest quality vapor barrier. Vapor barriers will be exposed to high foot traffic and extreme conditions during construction that can result in tears. Even the smallest holes can lead to water vapor emissions and expensive problems. It’s crucial that your material is strong and puncture-resistant.
Underslab vapor barriers are also required for residential buildings according to Section R506.2.3 of the 2019 International Residential Code (IRC) and must meet ASTM standards.
- ASTM E1745 is the standard specification for plastic vapor barriers under concrete slabs. This standard applies to the puncture resistance, water vapor permeance, and tensile strength and classifies materials in A, B, and C classes.
- ASTM E96 is the standard test method for water vapor transmissions. This standard applies to the measurement of water vapor permeability through a variety of materials.
Common Questions About Underslab Vapor Barriers
What can I use for a vapor barrier under concrete?
Plastic sheeting is the material most commonly used under concrete slab foundations, but not all plastic sheeting can be considered an actual vapor barrier — sometimes referred to as a moisture barrier for concrete. A proper vapor barrier undergoes multiple tests to measure how much moisture vapor or gas vapor can transfer through the material. These tests are expensive and timely, and many manufacturers are unwilling to invest in such an expense. The product’s technical data sheet can confirm that it meets the specifications for your project.
What’s the best mil thickness for under-slab vapor barriers?
A vapor barrier is available in thicknesses ranging from 6 to 20 mils, with a 6 mil being the most economical solution. Anything thicker than 20 mil is over the top. In technical terms, you are looking for high puncture resistance (durability) and low permeability (the amount of water vapor that can diffuse through the vapor barrier).
A 10-mil vapor barrier offers both, but a 15-mil or 20-mil vapor barrier offers premium protection because it is thicker and has lower permeability. The chart to the left shows how these rates compare among the different mil thicknesses and product types.
Is a vapor barrier the same as a moisture barrier for concrete?
In the construction industry, “vapor barrier” and “moisture barrier for concrete” are often used interchangeably to describe polyethylene sheeting installed beneath a slab. ASTM E1745 technically classifies these products as vapor retarders, with true vapor barriers referring to materials rated at 0.01 perms or lower. Regardless of terminology, the goal is the same: stop moisture vapor from migrating through the concrete slab.
High Quality Underslab Vapor Barriers
Vapor Barrier Yellow
Vapor Barrier Retarders are composed of polyolefin resins to create a puncture-resistant vapor barrier for use under concrete slabs to stop moisture migration and reduce mold, mildew, and fungus.
Vapor Barrier Blue
Vapor Barrier Retarders are composed of polyolefin resins to create a puncture-resistant vapor barrier for use under concrete slabs to stop moisture migration and reduce mold, mildew, and fungus.
Pro Crawl Barrier
Pro Crawl Barrier is a 10 mil Class 1 Vapor Barrier with a high gloss white finish offering low permeability and excellent tensile strength to protect the building fabric from moisture vapor damage. Roll size is 10′ x 100′.
Vapor Block Vapor Barrier
VAPORBLOCK® is a high performance crawl space vapor barrier designed to retard moisture migration through concrete slabs-ongrade. VAPORBLOCK® vapor barriers exceed ASTM E-1745 Class A, B, and C requirements.
Vapor Block Plus Vapor Retarder
VaporBlock® Plus™ 20 Mil Vapor Retarder/Gas Barrier is a seven layer co-extruded barrier made from state-of-the-art polyethylene and EVOH resins to provide unmatched impact strength.
String Reinforced Plastic Sheeting
Dura-Skrim® Reinforced Plastic Sheeting is a heavy duty construction and agricultural film excellent for both indoor and outdoor applications requiring an exceptionally strong material.
Vapor Barrier Tapes
A continuous underslab vapor barrier is the most effective against moisture control, but in most cases the material has to be cut to size, so using the appropriate tape to overlap seams and seal holes is very important. Americover supplies 2 Sided Butyl Tape as well as Vapor Tape for these applications.
R25B Seaming Tape
R25B Tape is an aggressive 8 mil single-sided liner seaming tape engineered to bond instantly to polyethylene and polypropylene surfaces — no heat welding required.
Butyl Tape
35mil thick double sided black rubber tape used to adhere overlapping panels of vapor barriers or vapor retarders together.
Vapor Tape
Heavy Duty, weather resistant, white sealing tape with a acrylic adhesive used for seaming large panels of vapor retarder.
Check out our online selection of specialty plastic building solutions. Contractors and distributors are eligible for special pricing and volume-based discounts on select products, call us at 760-237-8786. Our online inventory is just our retail selection, which means we can often source items you may not see here.
Contractors and Builders Talk About Americover
When you partner with Americover, you benefit from our industry and product application knowledge. But don’t take it from us. Take it from those in the building industry who have relied on our quality and reliability over the years.
Underslab Vapor Barrier Resources
Americover’s Product Catalog
Browse our full inventory of vapor barrier and crawlspace encapsulation liner products.
Guide to Selecting an Effective Vapor Barrier
Everything you need to know about choosing and installing a vapor barrier.
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