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I agree with your contractor.  You just can't wait long enough to dry the
slab if you are going to be adhering a membrane floor finish to the slab.
If you put down a thin sand lift, they will moisten it in order to be able
to work on it.  If you get a rain after the sand lift is prepared but before
the slab is cast, how will you dry it out?  If you use a good concrete mix
and wet cure the slab, you will not get much if any perceptible curling.  If
you do get a little curling, it will be easier to grind it out than to wait
for the slab and the sand lift to dry out.  Remember the moisture drawn out
of the concrete into the sand lift will eventually return to the interface
between the concrete and the floor finish.  The surface of the concrete may
test dry, the day you install the finish and be wet later because the
moisture has finally migrated to the surface of the concrete.  If the floor
finish is not a vapor tight membrane, then my opinion might change.

Roger Davis
SDS Architects, Inc
205 N. Dewey Street
Eau Claire, WI 54703

-----Original Message-----
From:	NDZ28(--nospam--at) [mailto:NDZ28(--nospam--at)]
Sent:	Tuesday, April 25, 2000 11:36 AM
To:	seaint(--nospam--at)

Just hoping I can get a basic question clarified. I  have a client  I'm
a series of homes for, and he wants me to specify that the slab on grade be
placed directly over the vapor barrier, (no sand between) He claims that
sand over the vapor barrier is moistened prior to pouring concrete, sand
 never dry out,  the moisture from the sand will travel through the slab for
a very long time causing bubbleing in the vinyl flooring, prevents  wood
flooring from sticking to concrete, etc. I've always believed that the sand
aids the curing of the slab.  The caveat is that vapor barrier is installed
properly and not punctured during placement of concrete. Any help is
Andy Vidikan