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RE: Capillary Breaks

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The material we used under the building slabs on our last Navy project was "Porous Fill".  I'm trying to find the specs on it.  In my memory, it was a coarse granular material with no fines.  Like a very coarse sand but not quite gravel.  I think some people call this torpedo sand.  It doesn't compact per se but does o.k. if confined.  The slabs came out beautiful - not a single crack, nicely steel troweled finish.  Concrete don't get no better than these slabs.  No vapor barriers were used on this project as the floors remained exposed concrete.
 
Bob Garner
-----Original Message-----
From: GSKWY(--nospam--at)aol.com [mailto:GSKWY(--nospam--at)aol.com]
Sent: Wednesday, February 09, 2005 2:04 PM
To: seaint(--nospam--at)seaint.org
Subject: Re: Capillary Breaks

In a message dated 2/9/2005 4:29:51 PM Eastern Standard Time, rgarner(--nospam--at)moffattnichol.com writes:
Not sure how relevant this is.  I've had cracking problems with slabs placed directly on vapor barriers.  There needs to ba a way for bleed water to exit the bolttom of the slab, and placing capillarity break material on top of the vapor barrier seems to help in this.  Also, this seems to provide some protection for the vapor barrier during bar and concrete placement.
 
Bob Garner, S.E.
 
I guess my comment on this is still - are you talking about a capillary break material or are you talking about a granular material?  These are not the same thing.
 
The ACI 302/360 recommendation is that if you have anything on top of the vapor retarder,  it should be compactible and trimmable.  The 'trimmable" bit is kind of useless,  since as far as I know there are no measures of "trimmability",  but compactible means that you have to have particles of different sizes - i.e. not capillary break material.
 
This is way big litigation material.  Not to be too specific,  but you start by looking up all the definitions you find for things like "capillary break" in any ASTM standard.  And you start looking at the ASTM specification for vapor retarders.  Which essentially copied the above chunk out of ACI 302 (trimmability and all.)
 
Also,  putting a granular material on top of the vapor retarder just for protection is generally not recommended - if you do puncture the vapor retarder, it's hidden. Doesn't mean it isn't done,  but you might not find any well respected documents recommending it.
 
Gail Kelley
 
-----Original Message-----
From: GSKWY(--nospam--at)aol.com [mailto:GSKWY(--nospam--at)aol.com]
Sent: Wednesday, February 09, 2005 11:53 AM
To: seaint(--nospam--at)seaint.org
Subject: Re: Capillary Breaks

In a message dated 2/9/2005 2:45:58 PM Eastern Standard Time, James.Lutz(--nospam--at)earthtech.com writes:
I think maybe the "capillary break" above a vapor barrier is just to provide somewhere for bleed water to go so it doesn't accumulate on the bottom of your slab. If there were no vapor barrier, you would want a real "capillary break" to keep the soil from pulling water out of the mix.
That was kind of my assumption too - but then you get into the ACI 302/360 discussion about whether there should be a granular layer above the vapor retarder.
 
And a capillary break needs to be more or less the same size particle so that it is very free draining.  And that kind of material is not easy to compact well.  Whatever goes on top of the vapor retarder has to be compactible.  So to call for a "capillary break"  on top of the vapor retarder does not seem to make sense.
 
I am not sure who the guy that wrote the article is - he's a salesman, for all I know his qualifications are that he has a degree in automotive technology. 
 
Gail Kelley
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