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RE: Vapor Barrier

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Jim,

One of the subs that specialize in floors and minimizing joints is Kalman.
Their practice is to put floors down in about 100' x 100' sections from
joint to joint.  They wrap the columns to allow movement relative to the
slab.  The slab is reinforced with rebar.  They use a proprietary mix with a
shrinkage compensation admixture.  The slab is placed with no thickened
portions on a well graded sub base.  The sub base is covered with plastic
and that is covered with a layer of geotech fabric.  The slabs sections are
doweled with the types that allow differential longitudinal movement.

The keys are their proprietary mix, quality control, and curing.

Keep in mind that ACI 302.1 is a guide not a code.  Requirements are not the
same in a guide.

If I do a conventional slab on grade with a vapor barrier, I prefer to use
crushed rock in lieu of sand.  It will not displace as easily.  

Harold Sprague, P.E.
The Neenan Company
2620 E. Prospect Ave
harold.sprague(--nospam--at)neenan.com


-----Original Message-----
From: Jim Kestner [mailto:jkestner(--nospam--at)somervilleinc.com]
Sent: Tuesday, October 13, 1998 11:06 AM
To: seaint(--nospam--at)seaint.org
Subject: Vapor Barrier


I would like to get opinions on what I consider conflicting requirements
regarding vapor barrier under slab-on-grade. ACI 302.1-R, 2.4.1 requires
that if a vapor barrier be used that it be covered with 3" of sand
before pouring the slab. This minimizes plastic shrinkage cracking and
curling. It also controls bleed water coming to the surface. This is
logical and well documented. However, this procedure is risky when
pouring a slab not under cover. What are the chances of rain occuring
after the sand is placed over the vapor barrier but before the slab is
poured? Now, you may have water trapped which could be very expensive to
deal with or if ignored, worse than having no vapor barrier at all.

It seems like ACI requirements address the finishing and performance
aspects of the slab, but have ignored the practical aspects of what the
contactor must deal with. How do you other Engineers and Contractors
deal with this?

Jim Kestner
Green Bay, Wi