CMU block veneer

[PSUengineer1]

Please identify the block veneer in the attached photo. I see it on many buildings built in the 1970s. The veneer is backed up by 8-inch CMU block.
thx.

 

[bridgebuster]

The pattern is stack bond BUT when I zoom in on the joints it looks like the same material as the "CMU"; I see what appears to be small pieces of aggregate in the joints. Are you sure this isn't a concrete wall with a form liner?

 

[Wallache]

Looks like scored face CMU to me.

http://www.basalite.com/products/masonry-block/cmu-concrete-masonry-units/scored

 

[Ron]

bb...that was my thought as well.

PSU....look for joints at modular dimensions, like 4 feet and 8 feet.

Any chance you could snake a borescope behind the veneer?

 

[concretemasonry]

Those units look like a CMU veneer (2-8x8 nominal faces per 15-5/8 long CMU) that was laid in a stack bond. - It can be easier for a veneer that avoids the 2:1 ratio of the common 8x16 CMU faces. Since it is a veneer for an 8" CMU, the strength of the wall is not affected. It also works well dimensionally for openings, corners, etc.

Dick

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

 

[msquared48]

"Since it is a veneer for an 8" CMU, the strength of the wall is not affected. It also works well dimensionally for openings, corners, etc."

Not entirely true for a high seismic application with the additional dead load of the veneer on the wall to consider.


Mike McCann, PE, SE (WA)

 

[hokie66]

I can't really tell from the photo, but if it is scored face, it was probably laid in running bond to look like stack bond.

 

[concretemasonry]

Hokie -

For a single scored CMU (2 - 8x8 nominal faces), the appearance of the CMU wall will be the same for both stack and the common running bond. - It is a grid of 8x8 squares with the joints and scores lining up.

If you look very closely at the joints, you can see small a surface difference in the texture or surface. The joints will have a smoother, denser appearance and the texture may show a slicker face than the joint tooling. The differences are usually masked by depth and shadows of the "racked" joints. For other types of jointing (concave or "V" joints) it can more noticeable, especially if the CMU face have a coarser texture.

Very often, for single scored CMUs, many contractors and manufacturers will score both sides of the CMU to permit the use of a slightly chipped CMU and use the best face exposed for veneers.

Dick

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

 

[hokie66]

Dick,

I know that. I was just pointing out that this wall may be laid in running bond, as opposed to the statements above that it is stack bond, but my eyes are not good enough to tell from the photo. If I were looking at the wall itself, I would know.

 

[concretemasonry]

hokie66 -

I had a problem also since my eyes are probably older than yours and I did not download and enlarge the photo.

It certainly is a tough call on the stack bond construction or running bond because often a mason will drag the skimmer along the head joints while finishing to even out the colors. - Some architects even require this, especially with ground face, colored or scored (1 score, 2 score or 3 scores per unit) architectural units. Since the wall is about 40 years old the mortar has cured, weathered and bleached out to come close the CMU color.

The common terms of running bond and stack bond are NOT the only description for bonding from a structural standpoint. Some people refer to another term - "other than running bond" that put a requirement for bonding to qualify for codes based on the decades of wall testing. I know that a 4" offset (1/4 of the unit length) can meet the necessary condition for use in running bond. I do not know if the 1/3 bond (5-1/3") does qualify, that is not too common except for some architectural or specialty structural units.

Structural masonry design is difficult for most engineers to comprehend, since it refers to a wall performance using different materials/products with different strengths and different h/t ratios. Fortunately the strength of the mortar has little effect on the wall strength and that is why the procedure/standard for field testing of mortar was discarded after bring on the table for decades.

Dick



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