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RE: Portlands vs. Blended Hydraulics

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See Below.
 
Harold Sprague
The Neenan Company 
 

-----Original Message-----
From: Robert Rollo [mailto:rrollo(--nospam--at)TEAM-PSC.com]
Sent: Friday, June 04, 1999 3:27 PM
To: 'seaint(--nospam--at)seaint.org'
Subject: RE: Portlands vs. Blended Hydraulics


thanks harold for the thoughts on blendeds 

how about another one . . . 

is there chemical difference between portland plus lime and masonry cements
?   
or are masonry cements simply premixed with the lime ?  
They are proprietary.  Some are 1/2 cement and 1/2 crushed limestone.  Some
are 1/2 cement and lime.  Some have air entraining agents.  Some have other
stuff.  Limestone is inert and does not have the cemetitous or crack healing
properties of lime.  
 
Because of the problems (I don't know what is in them) with masonry cements,
I avoid them.
 
seems like i had heard once (with no confirmation) that portland plus lime
is better 
than allowing masonry cements, primarily due to the leaching of salts
responsible for efflorescence. 
we typically spec ASTM C270 proportion spec for S with portland and lime for
this reason. 
have i lost my mind on the efflorescence and should i be performance
spec'ing and forget the efflorescence issue ?  
 
There are other issues, but efflorescence is a major issue.  You don't know
what is in masonry cement.  But watch your details (cavity, weeps, mortar
bridging, etc.).  The details cause more efflorescence than anything else.
Even the best materials can leach salts. 
 
Stay with the cement & lime, but consider using type N mortar whenever
possible.  The additional lime will heal cracks better, and the additional
board life will improve the look and workmanship of the finished wall.   
 
Take a look at some of the Mortar Net products for maintaining the cavity
and providing weeps.  And don't use corrugated strap masonry ties.

thanks in advance.