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RE: purposely permeable concrete

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Russ -
  I've also encountered this problem. A few years past, I was the PM for the
upgrade of an existing 30 year old building. Part of the upgrade included
replacement of a VAT flooring located in the lobby with rubber flooring.
After in-place for a few months, several of rubber tiles lost their bond to
the 5" concrete slab on grade. When a tile was removed, moisture was
evident. Prior to placement of the new flooring, water vapor transmission
tests occurred per the flooring manufacturer's requirements. However, said
tests occurred after all of the existing VAT was removed(lessons learned).
The new rubber flooring apparently acted as a watertight membrane while the
VAT was a lot more permeable and didn't trap the water vapor. It was also
subsequently discovered that no vapor barrier occurred below the slab.

Charlie Canitz 

> ----------
> From: 	rnester(--nospam--at)juno.com[SMTP:rnester(--nospam--at)juno.com]
> Reply To: 	seaoc(--nospam--at)seaoc.org
> Sent: 	Tuesday, June 09, 1998 12:23 AM
> To: 	seaoc(--nospam--at)seaoc.org
> Subject: 	purposely permeable concrete
> 
> Permeable concrete sounds like a guarenteed failure for the flooring. 
> The planned sheet vinyl flooring will then become the vapor barrier, even
> if the concrete is of normal porosity.  In dozens of buildings built in
> the 1960's and 70's, I have seen two interesting rphenomena.  The first
> is that the water pressure will eventually lift the flooring off, glue
> and all.  The second is that the concrete underneath will be dark,
> indicating water saturation.  In the most extreme case, with a more
> modern urethane floor, blisters formed on the flooring, and if punctured
> would actually squirt water.   Similarly, plywood or OSB placed on a slab
> w/o a proper vapor barrier will swell and raise up, eventually requiring
> total replacement. If the flooring is to last, there must be an effective
>  vapor barrier under the slab.  
> 
> Russ Nester
> rnester(--nospam--at)juno.com
> 
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