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RE: Visqueen under slab in Arizona

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George,

The reason for the Visqueen is to serve as a vapor barrier.  

If concrete is placed directly on top of Visqueen, 3 things happen:
	1.	The slab will have excessive curl
	2.	Unless you use 10 mils or greater, the Visqueen will have
many punctures
	3.	Concrete placed directly on top of Visqueen will result in
the degradation of the Visqueen due to the 			alkalinity
of the concrete

The purpose of retarding the vapor is to assure that any adhered finishes
will not be damaged by the water vapor migrating up through the slab.

If water vapor is not desirable, I would:
	1.	Use a capillary break of open graded crushed rock as a base.
	2.	Provide a vapor barrier like the Mirafi or some other real
barrier
	3.	Provide a layer of compacted crusher fines over the vapor
barrier
	4.	Place the concrete on the crusher fines.

I have seen good performance on slabs on grade with no vapor barrier with
glued carpet and vinyl tile, but these slabs were on coarse sand.  And I
have seen delamination of seamless flooring on slabs on grade with vapor
barriers.  It is a function of the finish sensitivity, and the tendency for
water vapor to form.  I like a capillary break, no matter what (don't put a
SOG on clays or silty sands).

Regards,
Harold Sprague

> -----Original Message-----
> From:	George Richards, P.E. [SMTP:george(--nospam--at)BORM.com]
> Sent:	Monday, January 17, 2000 12:39 PM
> To:	'seaint(--nospam--at)seaint.org'
> Subject:	Visqueen under slab in Arizona
> 
>  We are being told that it construction practice in Arizona along the
> Colorado river is to not place Visqueen under residential floor slabs.
> Would anyone please comment.
> 
> George Richards, P. E.
>