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Fwd: Re: Location of Vapor Barrier Below Concrete Slab on Grade

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I would also like to add some comments since this subject gets discussed
periodically in our office (up in Portland Oregon)

>From talking to some developers and contractors,   even with the vapor
barrier installed properly under ideal conditions, many projects don't get
the warranty from the flooring folks as they test the finished concrete slab
for acceptable limits on various chemicals and it often fails to meet all of
the requirements.  This usually results in the floor being applied without
the anticipated warranty.

A nagging problem up here in the Pacific Northwest with the vapor barrier is
it usually rains (a lot lately) after the vapor barrier, sand, and rebar are
placed but before the concrete slab is poured.  Do you take out the sand and
start over fresh, try to dry the sand out, or punch holes in the vapor
barrier to drain the free standing water?  Usually its holes in the vapor
barrier due to the cost and the warranty item above.

Walking on wet sand (previously compacted) after a good rain also creates
nice deep foot prints.  We try to get the contractors to smooth their
footprints while pouring but basicaly end up with a 4" slab that may be as
little as 3" deep in many spots due to the saturated sand moving.  It seems
to me that structurally we would get a better slab system the majority of
the time without the vapor barrier or should be using a gravel based
material over the vapor barrier for better compaction.  

Anyway, we still use the vapor barrier in our standard slab details as it
shows up in most of the soils reports, however, we also have some developers
who choose not to install it. 

Peder Golberg, P.E.

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Subject: Re: Location of Vapor Barrier Below Concrete Slab on Grade
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Richard Lewis, P.E.
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