Need a book? Engineering books recommendations...

Return to index: [Subject] [Thread] [Date] [Author]

RE: Capillary Breaks

[Subject Prev][Subject Next][Thread Prev][Thread Next]
Gail, I agree with you that a "capillary break" should not be required
above a vapor barrier - this seems to be a "belt and suspenders"
approach. But I do think that a "compactable, granular material" should
be used between the vapor barrier and the bottom of concrete.  

I have been searching for a specification for a granular material to
place on top of the vapor barrier, to conform the recommendations of ACI
302.1R. The ACI guide is not written in enforceable specification
language. Do you have any suggestions for specifying this material? 

I am considering using the local DOT base course material (e.g., "ABC" =
aggregate base course). This seems to have the qualities of being
compactable and granular. 

William C. Sherman, PE
(Bill Sherman)
CDM, Denver, CO
Phone: 303-298-1311
Fax: 303-293-8236
email: shermanwc(--nospam--at)


	From: GSKWY(--nospam--at) [mailto:GSKWY(--nospam--at)] 
	Sent: Wednesday, February 09, 2005 3:04 PM
	To: seaint(--nospam--at)
	Subject: Re: Capillary Breaks
	In a message dated 2/9/2005 4:29:51 PM Eastern Standard Time,
rgarner(--nospam--at) 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) [mailto:GSKWY(--nospam--at)]
			Sent: Wednesday, February 09, 2005 11:53 AM
			To: seaint(--nospam--at)
			Subject: Re: Capillary Breaks
						In a message dated
2/9/2005 2:45:58 PM Eastern Standard Time, James.Lutz(--nospam--at)

				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

******* ****** ******* ******** ******* ******* ******* ***
*   Read list FAQ at:
*   This email was sent to you via Structural Engineers 
*   Association of Southern California (SEAOSC) server. To 
*   subscribe (no fee) or UnSubscribe, please go to:
*   Questions to seaint-ad(--nospam--at) Remember, any email you 
*   send to the list is public domain and may be re-posted 
*   without your permission. Make sure you visit our web 
*   site at: 
******* ****** ****** ****** ******* ****** ****** ********