A concrete vapor barrier is simply a sheet of polyethylene plastic (Visqueen) placed directly on top of the sub-grade before the concrete floor or slab is poured to help keep moisture from the soil from passing up through the concrete.
Many moisture problems associated with interior concrete floors and slabs on grade can be minimized or eliminated by installing a vapor barrier under the concrete.
A vapor barrier should be used for all concrete floors and slabs that are going to receive an impermeable floor finish like epoxy, laminate, linoleum, and wood or if the concrete floor will be used for any purpose where the passage of water vapor through the floor may create problems.
Water vapor that passes through the concrete will evaporate if the concrete surface isn't sealed or covered by a material that doesn't allow the concrete to breathe. Floor coverings like linoleum, vinyl tile, wood, carpeting, and epoxies, seal the moisture in the concrete where it eventually causes the floor covering to loosen, blister, or buckle.
Things you should know about Visqueen or polyethylene plastic sheeting used as a vapor barrier.
1. Visqueen or Poly is made from low grade resins and recycled materials that can break down over time.
2. Poly vapor barriers usually do not meet the new guidelines for puncture resistance.
3. Most poly vapor barriers don't meet the permeance rating of .10 or better, which means they still let moisture pass through the concrete.
4. Visqueen polyethylene is better called a vapor retarder as it really just slows the passage of moisture through the concrete and doesn't really
block or create a true impermeable barrier.
What kind of concrete vapor barrier should I use?
New generation vapor barriers made from the highest grade, virgin, polyolefin resins have been developed that are considered true below slab vapor barriers or concrete vapor blockers. These 10 mil and 15 mil vapor barriers are very puncture resistant and will not break down over time, creating a true moisture barrier between the sub-grade and the concrete floor.
I've personally used Stego Wrap's 15 mil vapor barrier. It comes in a 7 foot roll that unfolds to 14 feet wide by 140 feet long. It's quite easy to
install and Stego has a special tape to seal all the seams and around protrusions to create a true barrier. In the past, I've used 6 mil poly as a vapor barrier under concrete floors and slabs and will say it is easily punctured, the Stego Wrap is much more puncture resistant.
There are other manufactures like W.R. Meadows that make equivalent vapor barriers to Stego Wrap. W.R. Meadows vapor barrier is called Perminator, it also comes in 10 mil and 15 mil thicknesses.
What is moisture vapor transmission in concrete?
How to test for moisture in a concrete floor and slab.
How thick should my vapor barrier material be?
What is the best concrete vapor barrier?
How much does a concrete vapor barrier cost?
Learn how to install a vapor barrier correctly.
What you can do if you have too much moisture in your concrete floor or slab.