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RE: Masonry Cement

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Roger, why do you say "prism tests are certainly not good tests"? 

Regarding mortar, ASTM C270 provides for compressive strength testing of
mortar (per ASTM C109) using a specific quantity of water. Since the amount
of water included in field mixed mortar is  not so well defined, compressive
test results of field mixed mortar cannot properly be compared with the lab
compressive tests. C270 even states that it "is not a specification to
determine mortar strengths through field testing". ASTM C780 can be used for
preconstruction testing and mortar testing during construction, including
compressive strength. However, C780 also states that "the test results
obtained under this test method are not required to meet the minimum
compressive values in accordance with the property specifications in
Specification C270" but such compressive strengths are to be considered
"approximate mortar strengths because lower water-cement ratios mortars are
more probable in the wall than can be measured for mortars from the mixer".
Thus it is inappropriate to require field mixed mortars to meet any specific
compressive strength requirement. 

> -----Original Message-----
> From: Roger Davis [mailto:rdavis(--nospam--at)sdsarch.com]
> Sent: Monday, July 02, 2001 6:20 AM
> To: seaint(--nospam--at)seaint.org
> Subject: RE: Masonry Cement
> 
> 
> For field testing, ASTM C270 is a measure of consistency but 
> it does report
> a measure that is described as the compressive strength of 
> the mortar.  The
> result is not a legitimate measure of strength but it tends 
> to be used as
> one.  There doesn't seem to be any good test for mortar or masonry
> assemblies, prism tests are certainly not good tests.
> 
> Roger C. Davis
> Architect
> SDS Architects, Inc.
> 
> 
> -----Original Message-----
> From:	Sherman, William [mailto:ShermanWC(--nospam--at)cdm.com]
> Sent:	Friday, June 29, 2001 5:56 PM
> To:	'seaint(--nospam--at)seaint.org'
> Subject:	RE: Masonry Cement
> 
> Roger Davis wrote:
> 
> > With site mixed, many times you get mortar that is way to 
> strong.  Masons
> know that if
> > the mortar is tested and the strength is low, they have a 
> problem.  Hardly
> 
> > anyone will complain about being over-strength.  Pre-mixed should be
> > closely in strength to what you specified.
> 
> But normally masonry mortar is not field tested, since there is no
> established compressive strength for mortar in the field 
> (i.e., ASTM C270
> only applies to laboratory specimens). So why should masons 
> be so concerned
> with strength of site-mixed mortar?
> 
> 
> 
> 
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