Vapor retarders
Vapor retarders can provide a very effective and necessary means of retarding
the amount of moisture transmitting through slabs-on-ground from sources below.
While often referred to as vapor barriers, few such materials truly provide a
100% barrier to rising moisture and therefore are more accurately referred to as
vapor retarders.
The effectiveness of
a vapor retarder is dependent upon many factors. The material must be strong
enough to resist construction traffic and puncture. It must exhibit very low
permeability and be constructed of material resistant to long term decay. The
vapor retarder must be installed carefully and be sealed at all seams,
penetrations and at the perimeter. For most floor covering applications the
vapor retarder should be placed directly beneath the concrete and design
measures utilized to resist the curling or warping of the slab.
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Many types of
extremely low permeable floor coverings such as rubber and sheet vinyl warrant
the use of the lowest permeable vapor retarder materials available. When such
floor coverings are used over higher permeable vapor retarder materials,
moisture related problems have been found to develop as the moisture content of
the concrete increase over time.
Thickness alone is
not always a reliable yardstick of the performance of a vapor retarder material.
Many thinner high density materials easily outperform thicker low
density materials. |
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Copyright 8/95, revised 8/98, P.
Craig
Special thanks to Mr. Peter Craig for his contribution of this page |
The selection of the vapor retarder material should be made on the
basis of physical properties, composition and on the requirements of the floor
covering system.
Research into
moisture-related floor covering problems has shown a high correlation between
the absence of an effective vapor retarder and flooring failures. All too often
vapor retarders are omitted when the water table is determined to be well below
the building site and free draining soils are utilized beneath the slab. However
without an effective vapor retarder in place the vapor pressure differential
above and below the slab can contribute to moisture rising through soil and
concrete. This moisture will condense at the slab surface and can potentially
initiate several of the mechanisms of floor covering failures.
The investment in a
high quality vapor retarder material, properly installed directly beneath
concrete slabs-on-ground is inexpensive insurance against one major avenue of
costly moisture related floor covering and coating failures.
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