Need a book? Engineering books recommendations...

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

RE: Vapor Barrier

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

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
3.  A vapor barrier.
4.  A well graded 3" gravel layer (heavy on the fines, I prefer quarry
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

Harold Sprague, P.E.

-----Original Message-----
From: Donald L. Carr [mailto:dcarr(--nospam--at)]
Sent: Wednesday, October 14, 1998 2:26 AM
To: seaint(--nospam--at)
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
NAHB Research Center, Inc.
400 Prince Georges Blvd.
Upper Marlboro, MD 20774
301-249-4000 x575