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Get a copy of ASTM E1643-94.  An excellent discussion and specification on this
subject. (It agrees with your architect.)  The sand can cause some serious
chuck Utzman

Gary Chock wrote:

> Don't be too quick to discount potential problems with vapor transmission.
> There have been problems with delamination of adhesively applied flooring
> due to vapor pressure.  In this region, it has been observed in private,
> state, and federal projects.
> Apparently, the adhesives used in modern times is more susceptible to vapor
> transmission.  The flooring industry has adopted moisture emission
> standards that can be difficult to meet in a timely manner.
> The sand or fine-grain aggregate layer can potentially contribute to this
> by accepting water from the freshly placed concrete (which is why it would
> be placed there).  The potential benefit of this reservoir of moisture to
> aid slab curing may also have a disadvantageous long term effect on
> flooring.  There are various products, such as floor sealers designed to
> limit vapor transmission, that are available.
> You might consider discussing  this issue and the sand layer with your
> architect, and let him make the call after consideration of the potential
> benefits and disadvantages.  It's not solely a structural decision.
> Gary Chock
> At 12:35 PM 4/25/00 EDT, you wrote:
> >Just hoping I can get a basic question clarified. I  have a client  I'm
> doing
> >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
> when
> >sand over the vapor barrier is moistened prior to pouring concrete, sand
> will
> > 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
> >appreciated.
> >Andy Vidikan
> >
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