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

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And also consider using a heavier "barrier" to reduce the chance of
puncturing it.  I have been "taught" to use at least a 10-mil below the
graded material.

Scott Maxwell, PE, SE


On Thu, 31 Aug 2000, Mark Gilligan wrote:

> 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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