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RE: Vapor Barrier

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Speaking of Masterspec, the latest one has the thickness as 10 mil. 
Needless to say we have been challenged on this.  Does anyone know why the
increase in thickness?  Is it because of degradation.  I saw an article in
one of the concrete magazine that showed where old vapor barriers were dug
up to see how they were aging.  After only a few years there were holes the
size of 50 cent pieces all over the place.  Just curious.
 
John Jones
Pell City, AL

-----Original Message-----
From: Robert Rollo [mailto:rrollo(--nospam--at)TEAM-PSC.com]
Sent: Wednesday, October 14, 1998 3:47 PM
To: 'seaint(--nospam--at)seaint.org'
Subject: RE: Vapor Barrier



I think that about sums up everything I ever heard to use the ol' 6mil
visqueen for . . .
And while we're here, is it barrier or retarder?  Po-tay-to / po-taht-o :-)
I personally have a pet peeve and have seen a change order granted to a GC
where the details call it barrier, but the Masterspec section calls it
retarder.

We have always used 2" of clean sand dampened before the pour.  Does the
benefit of more sand justify the cost?

	-----Original Message-----
From:   Harold Sprague [SMTP:harold.sprague(--nospam--at)neenan.com]
Sent:   Wednesday, October 14, 1998 3:35 PM
To:     'seaint(--nospam--at)seaint.org'
Subject:        RE: Vapor Barrier

	Don,

	Let's call it plastic, and it can do whatever you want.  It can serve as a
vapor barrier, it can serve as a control for curling, and it can serve as a
method to develop a slip plane for maximizing joint spacing.

	On general warehouse slabs on grade with as many joints as I want, I do not
use it.

	For any space that may get a floor covering, I use it.

	For joints spaced at greater distances than the standard for slab-on-grade,
I use it.

	To control moisture in an area with a finished floor:
1.  I require a well graded sub grade. 
2.  A layer of open graded clean crushed rock.  This serves as a capillary
break.
3.  A vapor barrier.
4.  A well graded 3" gravel layer (heavy on the fines, I prefer quarry
tailings).
5.  A concrete slab reinforced with rebar, and control joints placed with a
Soff Cut saw or tooled, with alternate rebar cut to form a 4" space.

	If the plastic is placed directly on grade (assuming clay), any water
migrating laterally will perch on the plastic and cause a damp slab.  If the
grade has good drainage characteristics, the plastic can be placed on grade
with no problem.

	And yes I require them on any residence I am asked about.  They might not
want a rec room now, but they will.  Loading is irrelevant to vapor
barriers.

	Harold Sprague, P.E.
harold.sprague(--nospam--at)neenan.com


	-----Original Message-----
From: Donald L. Carr [ mailto:dcarr(--nospam--at)nahbrc.org]
Sent: Wednesday, October 14, 1998 2:26 AM
To: seaint(--nospam--at)seaint.org
Subject: Re: Vapor Barrier


	I have been following the discussion of the vapor barrier and the
sand or gravel layer under a slab.
Can anyone help me with a question?
 " Is this a detail you would specify for a commercial slab
on grade design, a residential slab design, or any ground slab design
depending on the loading conditions?"
Thanks for your opinions.
Don Carr

	Donald L. Carr
dcarr(--nospam--at)nahbrc.org
NAHB Research Center, Inc.
400 Prince Georges Blvd.
Upper Marlboro, MD 20774
301-249-4000 x575
http://www.nahbrc.org


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