Cracking of mortar joints in new cmu wall 1

[Gopher13]

I have a newly constructed building with cmu walls. The building is approximately 250 feet long by 24 feet wide with a roof overhang of 8 feet on all sides. The top of cmu walls are 8'-8" above finished floor elevation. Window openings are 4 feet wide and are spaced at every 4'-8" on center. Two cores are grouted and reinforced on each side of each opening as well as one core between each opening. Vertical control joints are spaced at approximately every 16 feet and each adjacent core is grouted and reinforced. Type S mortar was used.

There are a lot of vertical cracks in the mortar joints right where the mortar bonds to the block. What could be causing these cracks? Is it happening because there is too much grouting and reinforcing in the walls? Should there be more control joints?

Thanks!!!

 

[concretemasonry]

Do the block cores align vertically to provide a clean vertical grout space? - Most block core do not align perfectly and grout can leak into adjacent core spaces. - A 2 core unit with a small end core will not provide clean grouting spaced that cannot leak laterally.

A 16" long block with one core and 2 webs at 8" o.c. provides perfectly aligned grouting.

Dick

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

 

[Gopher13]

Yes, I believe the block cores align vertically.

 

[SLTA]

pics of the cracking?

if the wall was built in the super cold, and now it's not, it could be temperature differential.

Please remember: we're not all guys!

 

[Gopher13]

Block was placed in the fall. Temperatures were favorable.
Up close picture attached. Typical throughout building.

 

[JLNJ]

We did a school where the weather overcame the heat of hydration and the grout in the jambs froze and cracked the units. Obviously, the wall was not properly protected from the elements.

How were the control joints detailed? Did the contractor happen to continue the horizontal reinforcement through the joint?

 

[JAE]

That's pretty minor - but probably could be due the units shrinking a bit.

With joints at 16 ft. o.c. I can't see how the overall wall shrinkage could be the direct cause.
If the joints weren't made properly and still had some through-joint connectivity, then perhaps some overall wall shrinkage cracks might occur.
This usually is the case in top-of-wall bond beams where the reinforcement was continuous.





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[dik]

The original photo shows snow and a wide open building... maybe thermal due to cold?

Dik

 

[Gopher13]

Horizontal joint reinforcement was not continuous through control joints.
There is a bond beam at the top with (2) - #5's continuous through the control joints.
Yes, cracks are minor, but there seems to be a lot of them. The mason claims they are a result of the amount of vertical reinforcing and grout in the walls.

 

[oldestguy]

I'd suspect the mortar was very wet and before it fully set there was evaporation and it shrunk some and even new block could have some similar mechanism along with temperature shrinkage. I'd not be concerned with the situation however.

Do a Google search and there is plenty out there on mortar shrinkage. Here is one.

tps://link.springer.com/article/10.1007/BF02481617?no-access=true

 

[SLTA]

I agree with oldestguy. I'd honestly call that a separation instead of a crack. I don't think it's a problem.

Please remember: we're not all guys!

 

[hokie66]

That is just poor workmanship on the part of the blocklayers. The mason's contention of too much reinforcement and grout makes no sense. If he honestly thinks that, he knows little about concrete masonry.