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

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At 02:40 PM 9/4/96 +0500, Bill Sherman wrote:
>According to the 1993 "Masonry Designer's Guide" by The Masonry Society: "Do 
>not use a higher compressive strength mortar than necessary....Unless dictated 
>by the compressive strength requirement, avoid the selection of Type M mortar 
>over Type S mortar.  However, when masonry is in direct contact with soil, 
>e.g. in retaining walls, Type M mortar should be used regardless of strength 
>According to PCA IS278.01M, "Factors affecting Bond Strength of Masonry": 
>"...the finding that little or no increase in bond strength is achieved by the 
>use of Type M mortars as compared to Type S mortars".  
>Type N mortar is considered better in Colorado's dry climate since it has 
>holds moisture better and doesn't dry out as quickly, although Type S can be 
>used.  Type M mortar is a harsher mortar.  Bond may be more important than 
>compressive strength and if the mortar dries out, it may not bond well. 
>I recommend specifying/ allowing Type S mortar for most structural 
>Date: 03 Sep 96 18:49:26
>From:"Mark Deardorff" <markedd(--nospam--at)>
>To: seaoc(--nospam--at)
>Subject: [SEAOC] Type M vs Type S mortar
>Reply-to: seaoc(--nospam--at)
>X-Orcl-Application: Organization: Deardorff & Deardorff, Inc.
>X-Mailer: Forte Agent .99e/32.227
>X-Orcl-Application: Precedence: list
>X-Loop: seaoc(--nospam--at)
>X-Orcl-Application: content-length: 1264
>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

This has been an interesting thread, but quite frankly it is an office
discussion. Here in seismic zone 4, I have not inspected one building yet
that has been specified for type M mortar. All have been type S. Also,
frankly, all the compressive strength mortar cubes have broken at 4000-5000
psi. As all masonry projects are fully grouted and reinforced, all that
matters is prism testing on a periodic basis. Mortar is just a way to level
the blocks.