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RE: sand layer under slabs - was ACI or CRSI question-answer center

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Scott,

Do you or anyone know what ASTM or DOT number to use for
the "blotter" material?  We are trying to find a specification
for this material.

Thanks

Brian Spencer
Tylk Gustafson Reckers Wilson Andrews, LLC
407 South Dearborn, Suite 900
Chicago, IL 60605
bspencer(--nospam--at)tgrwa.com
http://www.tgrwa.com 


>
>Ken,
>
>First of all, the most current recommendation on the "blotter" layer (if I
>recall correctly) was to use a layer of "crushed fines" or something
>similar.  The idea was to have a layer of something that would allow the
>moisture from the bottom side of the slab to migrate into that layer
>allowing the slab to cure.  Initially, the recommendation was sand (which
>allows movement of moisture relatively well).  The problem with sand is
>that it gets "mushed" during construction (i.e. placement of rebar,
>placement of concrete, etc) which can destroy the nice uniform surface.
>Thus, the idea of using something like a well-draining crushed fines that
>can compact relatively well and not be distrubed during the rest of the
>construction process.
>
>The recent change has been with the use of the "blotter" layer with a
>vapor barrier.  Recent information indicates that this formerly
>recommended system (a "blotter" layer under the slab but on top of the
>vapor barrier) can create problems with some moisture susceptible flooring
>materials.  The problem arrises from the fact that any moisture that gets
>trapped between the vapor barrier and the bottom of the slab in the
>"blotter" layer (i.e. rains after placement of the vapor barrier and the
>"blotter" layer but before the placement of the slab and not enough time
>is allowed for the "blotter" layer to dry; "excessive" moist cure that
>causes moisture to get in to this layer; wetting of the "blotter"
>layer prior to placement of concrete...a common/required practice; etc)
>can only go in one direction...up through the slab.  The potential result
>is that the moisture/vapor emmision rate could be high enough to cause
>some flooring materials to fail.
>
>The result is that ACI 302 and 360 issued a revised flow chart for
>determining when to use vapor barriers and what other conditions should be
>required with or without the vapor barrier.  This was issued in the spring
>of 2001 in an issue of Concrete Construction.  Additionally, the revision
>should be included with any new purchases of the main ACI 302 or 360
>documents and likely the MCP.  This subject was discussed on the list a
>couple of months ago...take a look at the archive.
>
>HTH,
>
>Scott
>Ypsilanti, MI
>
>
>On Tue, 5 Nov 2002, Ken Peoples wrote:
>
>> Is this true?  Is the sand layer no longer recommended?
>>
>> Kenneth S. Peoples, P. E.
>> Lehigh Valley Technical Associates
>> 1584 Weaversville Road
>> Northampton, PA 18067-9039
>> Phone: (610) 262-6345
>> Fax: (610) 262-8188
>> e-mail: kpeoples(--nospam--at)lvta.net
>>
>> ----- Original Message -----
>> From: "Roger Davis" <rdavis(--nospam--at)sdsarch.com>
>> To: <seaint(--nospam--at)seaint.org>
>> Sent: Tuesday, November 05, 2002 8:06 AM
>> Subject: RE: ACI or CRSI question-answer center
>>
>>
>> > Scott,
>> > That warm fuzzy feeling is what I wanted.  Questions seldom 
>come up until
>> > you need an answer.  I want immediate feedback so I can 
>continue with the
>> > work that brought up the question.  The answers that you and others
>> > contribute on this list have confirmed some of my opinions and made me
>> > change my mind on some things and educated me on many others - 
>they seldom
>> > come with any authority like a ruling from an ACI committee  but that
>> > doesn't bother me. I judge for myself whether or not to accept 
>them - just
>> > like I did with the old ACI Committee recommendation to place 
>a sand lift
>> > under a concrete slab on grade. I think it was only appropriate under
>> > special circumstances even though the committee recommended it 
>for years
>> > until they recently reversed themselves.
>> >
>> > Roger C. Davis
>> > Architect
>> > SDS Architects, Inc.
>> >
>> > -----Original Message-----
>> > From: Scott Maxwell [SMTP:smaxwell(--nospam--at)engin.umich.edu]
>> > Sent: Monday, November 04, 2002 5:05 PM
>> > To: seaint(--nospam--at)seaint.org
>> > Subject: RE: ACI or CRSI question-answer center
>> >
>> > To clarify what Jay wrote below...
>> >
>> > What he states is absolutely correct if you want an "official"
>> > interpretation of something in an ACI document.
>> >
>> > On the other hands, if you want the opinion of an INDIVIDUAL who was
>> > involved with the creation of that document, then members of 
>committee's
>> > can give their own opinion.  The key is that it is the opinion 
>of that one
>> > individual, NOT an official opinion in any way.  It may be 
>that opinion is
>> > correct and co-insides with what the official interpretation 
>would be if
>> > rendered.  The end result is that getting the opinion from an 
>individual
>> > committee member or an ACI staff member (or staff member from 
>CRSI, PCA,
>> > PCI, etc) may give you a warm fuzzy feeling, but it is more or 
>less worth
>> > what you paid for it (i.e. nothing) if you want to use it in 
>any form of a
>> > legal or substantive arguement.
>> >
>> > So, to use Roger's example, the answer he got was only useful 
>to give him
>> > a warm fuzzy feeling.  Even though it came from a member of the 318
>> > committee, it was not in anyway an official answer or a 
>respresentation of
>> > what was actually meant other than that individual's opinion.
>> >
>> > FYI, ACI staff member when they do respond to technical inquiries will
>> > sometimes contact committee members to see if one is willing to get an
>> > opinion.  Not only does this potentially get a more 
>authoritative (notice
>> > the adj.) for the person asking the question, it can also 
>point out to the
>> > committee where there are some items of confusion that may need
>> > clarification in the next iteration of the document.
>> >
>> > HTH,
>> >
>> > Scott
>> > Ypsilanti, MI
>> >
>> >
>> >
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