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Masonry f'm

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I'd like to thank Michael Cochran & James Hagensen for their responses
to my post on masonry f'm.

I would certainly think that meeting quality assurance provisions by the
unit strength method of 2105.3.4 would be less expensive than by the
masonry prism testing method of 2105.3.2.

Under 2105.3.4, units and grout are to be tested for each 5000 sq. ft.
of wall area during construction and units are to be tested prior to
construction to show compliance to Table 21-D.

Under 2105.3.2, a set of five masonry prisms are to be built and tested
prior to construction and a set of three prisms are to be built and
tested during construction for each 5000 sq. ft. of wall area (using
full stresses in both cases).

It is tempting to try  controlling construction costs by specifying a
lower unit and grout strength (less material cost) and pay for prism
testing although this "roll of the dice" does not appeal to me.

I may yet discuss with the local testing lab their experience with unit
and mortar strengths which will in fact produce f'm=2500 psi and
consider material vs. testing costs.

Again, thanks to Mr. Cochran and Mr. Hagensen for their responses as
well as Shafat and Dennis for their efforts to make this forum a

Mark D. Baker
Baker Engineering