Need a book? Engineering books recommendations...

Return to index: [Subject] [Thread] [Date] [Author]

RE: Vapor Barrier

[Subject Prev][Subject Next][Thread Prev][Thread Next]
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