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RE: Specifying CMU block weights

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Joel/William:

Thanks for the update.  My info apparently is a little dated.  "Helps"
that I don't have the disposible income to go out and buy all the latest
ASTM specs!  ;-)

Scott
Adrian, MI


On Wed, 26 Jan 2005, Sherman, William wrote:

> Scott, ASTM C90 no longer recognizes "Type I and Type II" units. The
> engineer must specify moisture control requirements now, if they are
> desired.
>
> Availability should also be checked. I'm not sure what the availability
> of light weight units is in the northeast - as noted, I think that
> normal weight units are more common there. I don't recall where, but on
> one project that I had specified light weight units, the bidders asked
> if normal weight units could be substituted, due to availability.
>
>
> William C. Sherman, PE
> (Bill Sherman)
> CDM, Denver, CO
> Phone: 303-298-1311
> Fax: 303-293-8236
> email: shermanwc(--nospam--at)cdm.com
>
>
> > -----Original Message-----
> > From: Scott Maxwell [mailto:smaxwell(--nospam--at)engin.umich.edu]
> > Sent: Wednesday, January 26, 2005 7:34 AM
> > To: seaint(--nospam--at)seaint.org
> > Subject: Re: Specifying CMU block weights
> >
> > Jim:
> >
> > Lighter weight block is generally more absorptive and more
> > permeable than normal weight block.  This is due to the use
> > of less density lightweight aggregates or due to the more
> > porous structure if a foam agent is used to get the ligher weight.
> >
> > Over all, the more absorptive nature of light weight block
> > can affect the durability of the block.  So, if the block is
> > going to be subjected to many freeze/thaw cycles than you
> > should use normal weight block.  Also, if moisture
> > penetration is an issue, then normal weight is the way to go.
> >
> > Light weight block will tend to shrink more than normal
> > weight block, but to get really "accurate" you should get
> > current shrinkage data from the block manufacturer that is
> > (potentially) supplying your project.
> >
> > And if block strength is an issue, while you can get high
> > strength light weight block, generally normal weight high
> > strength block will be more economical.
> >
> > I would say that if you are dealing with a cavity wall where
> > the block will largely be protected from moisture, then light
> > weight block could be used as long as you account for the
> > shrinkage issues.  The other thing that you will likely want
> > to think about is whether you want Type I
> > (moisture-controlled) or Type II (nonmoisture-controlled)
> > block.  I would say for exterior applications (potentially
> > including cavity walls depending on your "warm fuzzy feeling"
> > tolerance) you would want Type I.
> > It is used where you need higher strength, resistance to
> > moisture penetration, and resistance to severe frost action.
> > This would generally be things like retaining walls or
> > basement walls or exterior walls where the block is directly
> > exposed, but could include exterior cavity walls.
> >
> > HTH,
> >
> > Scott
> > Adrian, MI
> >
> > On Wed, 26 Jan 2005, Jim Wilson wrote:
> >
> > > What are the do's and dont's for specifying CMU block
> > weights in the
> > > northeast?  I am under the impression that normal weight
> > blocks are to
> > > be used for exterior exposed CMU walls due to water resistance.  Is
> > > water the governing factor, or are there other design components to
> > > this decision?
> > >
> > > Would medium weight or lightweight block then be specified only for
> > > interior partition walls, or would they also be specified
> > for exterior
> > > walls that are protected behind a vapor barrier, such as behind a
> > > brick face?
> > >
> > > I am guessing that it would it be too confusing to mix
> > block types on
> > > a project for interior and exterior walls?  Seems safer to
> > use normal
> > > weight block unless medium or lightweight are explicitly
> > required for
> > > some reason.
> > >
> > > TIA,
> > > Jim Wilson
>
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