Need a book? Engineering books recommendations...

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

RE: Specifying CMU block weights

[Subject Prev][Subject Next][Thread Prev][Thread Next]
Scott, ASTM C90 no longer recognizes "Type I and Type II" units. The
engineer must specify moisture control requirements now, if they are

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)

> -----Original Message-----
> From: Scott Maxwell [mailto:smaxwell(--nospam--at)] 
> Sent: Wednesday, January 26, 2005 7:34 AM
> To: seaint(--nospam--at)
> 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

******* ****** ******* ******** ******* ******* ******* ***
*   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: 
******* ****** ****** ****** ******* ****** ****** ********