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[SEAOC] RE: [SEAOC] Type M vs Type S mortar

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The biggest issue from the masons perspective is board life.  M mortar has a 
shorter board life.  S mortar is much more prevalent outside of the west 
coast for most structural applications.  Generally in projects that I have 
worked on throughout the US, S mortar is specified for the perimeter and 
structural walls, M mortar is specified for back parging and below grade 

In applications where wind driven rain can be an issue, S mortar is 
generally accepted as superior to M mortar.  M mortar has a higher cement 
content, and will generally shrink more.  With M mortar being restricted to 
subgrade and back parging, board life is not as great an issue as it is once 
you start going up the scaffold.  S mortar's higher lime content also acts 
as a "crack healer".  See the article by Walker and Gutschick in The 
Magazine of Masonry Construction, July 1988.

Local practices:
Construction techniques and standards are highly regionalized in the US for 
masonry, wood, and for some specific steel details.  It becomes even more of 
an issue in foreign work where local rebar sizes and strengths are just one 
of many nuances encountered.

I am sure your plans and specs. are correct and accurate, but it is often 
better to try to accommodate local practices and avoid a dispute.  Unless 
the cost difference is significant, you may wish to use this as you owe me 

Black & Veatch
From: seaoc
To: seaoc
Subject: [SEAOC] Type M vs Type S mortar
Date: Tuesday, September 03, 1996 6:49PM

We routinely specify Type M mortar on jobs. No one has ever

We recently completed drawings for a high school in Colorado. We used
our standard specification for mortar and have received a request for
change to Type S. The contractor must not see it often. But he *did*
bid the job from plans that included the Type M spec. He will need to
credit my client.

Aside from strength what are the relative benefits of the two types of



Mark E. Deardorff, SE
Deardorff & Deardorff, Inc.
San Diego, CA