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Masonry f'm Inspection

Masonry f'm Inspection

Masonry f'm Inspection

Some Building Codes require f'm checked periodically. Does that mean having mortar checked by testing lab doing cube samples, or is it just observing mortar being mixed, from bags labeled correctly as to Type (M, N, S, etc) and CMU being placed?
I am specifically referring to NYC BC Chapter 17, Table 1704.3 (Level 2), and for that matter whatever the IBC 2015 also says for New York State work.

Of course its always a good idea to use labs to check mortar samples, but my question is specific to BC requirements.

RE: Masonry f'm Inspection

From a code standpoint, the f'm is determined by a 2 block high HOLLOW prism using the materials on the project.

The over-riding factor in determining the f'm is the compressive strength of the block, that can be verified by pulling samples. The strength of the actual mortar is not a major factor and can be verified by observing the mixing procedures and proportions.

Strength testing of mortar is only used for research and not for construction verification. The ASTM standard for mortar, in the the appendix note states that the weakest mortar should be used to take advantage of the other properties of mortar, such a workability.

You can get a 5000 psi f'm with 2200 psi mortar if you can even find a need for such strengths. It may require a higher strength block that can be verified or specified in advance of construction.

Testing of job site prisms is unreliable, costly and time consuming.

Read the ACI 530 document regarding the design and construction of masonry. - The ACI 530 is the "bible" for masonry design and construction domestically and internationally and is normal referred in most civilized codes.


Engineer and international traveler interested in construction techniques, problems and proper design.

RE: Masonry f'm Inspection

It no longer will be known by "ACI 530" as TMS has taken sole control of the publication (TMS 402 and 602)

Most of the time we avoid masonry prism testing and simply used proportional specifications for masonry.

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RE: Masonry f'm Inspection

agreed, JAE. Cube strength has little relationship to the actual in place wall construction. The confinement afforded by the CMU units as well as the large difference in strength observed with a non-porous mold and one that allows the water in the mortar mix to 'soak into it'.


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