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RE: Slab-On-Grade Vapor Barrier (One More Time)

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The question was asked "or has the wheel turned yet again?"

Yes things have recently changed.  ACI now recomends some graded material
instead of sand between the concrete and the membrane.   This is in one of
the reports in the ACI Manual of Practice.

Mark Gilligan


++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>Okay, I know this horse has been beaten into dogfood, but I'm slow (and
don't
face this that often).

Please remind me.

"Old" practice was to put e.g. 6-mil "Visquine" or equal directly under the
slab. Later it was discovered this was NOT a good idea, as the hydrostatic
pressure in the slab through-thickness weakened the cement (and caused the
slab
to cure more slowly at the bottom). This led to cracking and a not-so-great
slab.

LATER practice (this is where I'm fuzzy) was to put SAND directly under the
slab, THEN the Visquine. That way any water would bleed out of the slab
into the
sand, yet "new" water vapor wouldn't come up from the soil below.

Have I got that right, or has the wheel turned yet again?
<


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