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12" CMU fire rating

12" CMU fire rating

12" CMU fire rating

I am looking at a 12" cmu wall from 1970s. The drawings appear to show the wall grouted @ 48" oc. I am trying for find some fire rating dates for CMU from that era but not finding anything.

What be a good resource for this information?

Thank you.

RE: 12" CMU fire rating

It's a little fuzzy... but a 12" CMU of that era had a 2 hour rating if memory serves and if fully grouted had 4 hours... partially grouted I'm not sure. BART's suggestion of the NCMA is great... CMU walls were often filled with zonalite insulation to up the FRR of them.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

RE: 12" CMU fire rating

12" CMU was not common in the 1970's. Probably still the case. Too darn heavy to lift. 8" was more frequently used with pilasters as necessary.


RE: 12" CMU fire rating

Thank you all.

@BA, just checked the drawings again. Built in 1972, in Chicago. The drawings show "Wall reinforcing every second block course". Which likely means grout @ 16" oc.

RE: 12" CMU fire rating

WWTEng, I don't think that is what it means. I think it is referring to welded wire block reinforcement which is laid horizontally every second block course. There may be some vertical cores which are filled, but if they aren't shown on plan, they probably aren't there.


RE: 12" CMU fire rating

Quote ("Wall reinforcing every second block course")

Is that hor or vert reinf? Often had horiz rfg each second or third course.

12" block wasn't common, but was used back then... units were too heavy and masons did not like them to work with.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

RE: 12" CMU fire rating

"Course" means horizontal layers, isn't it? The vertical reinforcing/grout cell is usually specified as "#x @ xx" oc", and "grout solid every XXth cells" respectively.

RE: 12" CMU fire rating

BA, I think you are correct. That appears to be a reference to horz reinforcement.

RE: 12" CMU fire rating

Look up publications by Armand Gustaferro. They are all about fire ratings for concrete and masonry. Some of them give calculation procedures which are also contained in some building codes.

RE: 12" CMU fire rating

The fire ratings for concrete block are all about using the equivalent thickness method which are found in the NCMA TEK that BARetired linked. The horizontal joint reinforcement that everyone is talking about doesn't have much on an impact on the fire rating. In addition, the fact that this is a partially grouted wall also doesn't have much of an impact as the area without vertical reinforcement will be the "weakest" from a fire resistance standpoint. So when you determine the fire rating using equivalent thickness it will be of the ungrouted portion.

Also, 12" block are common in different parts of the country and in some cases two masons will install a 12" unit since they are heavier. But as many of you have noted, 8" block are more common and in many applications are all that are necessary (when the masonry isn't overdesigned :)).

BTW, have you seen the M.U.L.E or Material Unit Lift Enhancer: https://www.construction-robotics.com/mule/? This has helped out on many masonry projects and will help extend the life (careers) of masons. Check out the videos on their website too - its helps masons lift block over the vertical reinforcing.

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