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Best Plastic For A Vapor Retarder/Barrier

Posted by Nana Hinsley on Thu, Jan 27, 2011 @ 10:11

 Question:  What is the best plastic to use for a  vapor barrier?

Answer by Lee Hinsley: I highly recommend only Engineered Vapor Retarders/Barriers for any application where one wishes to reduce or control vapors.  If one goes with an engineered film that has been designed for this purpose, and passes some level of the ASTM E 1745, preferably Class A, then one can be well assured they have a quality product that will last when in contact with soil.  Today as in the past, huge numbers of structures are built with no vapor retarder, or almost as bad, using Construction/Ag Grade Polyethylene sheeting.  I strongly recommend using a vapor retarder under all building structures, and just as strongly recommend that only engineered films are used in this critical application.  The big problem with Construction grade film (aka Visqueen) is that it will normally degrade when in contact with soil, and this process is usually significantly underway within 2 years.  Anyone who has been around construction for any length of time has dug up this kind of product.  Ask yourself how often this sheeting is in one piece?  Does it still have the strength it had when buried?  Not likely in either case.  In addition, the Construction grade sheeting is not even guaranteed to be pinhole free when brand new.  It often has high levels of something called Slip agents.  These make it easier for the manufacturing plants to make this lowest grade of polyethylene quickly and inexpensively.  The slip keeps the tapes normally used on this type of sheeting from permanently sealing at the seams.  Vapor Barriers and Vapor Retarders are often used interchangeably, but the preferred term in the industry today is vapor retarder.

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Tags: Plastic for vapor barrier