Repairing cracks in CMU

[StrEng007]

I was wondering if anyone has experience using Helical Stitching Ties by Simpson Strong-Tie. On a larger scale, I'm trying to determine when simple vertical cracks in masonry are suitable to route and seal vs. reappoint with introduction of a new control joint vs reinforcing by means of horizontal reinforcing or ties.

I have Alexander Newman's "Structural Renovation of Buildings" book and it offers a great discussion on these types of cracks and why they occur. However, I'm looking for a more detailed explanation as to when each type of fix is most appropriate. I understand this has to do with the underlying conditions and whether or not the crack is active or stabilized.

Keep in mind, this question pertains to vertical cracks in CMU due to expansion/contraction from moisture/thermal conditions and differential movement. I'm not talking about cracks due to overloading or structural failure via in-plane shear or out-of-plane flexure.

https://www.strongtie.com/accessories_restorationsolutions/helist_tie/p/heli-tie

 

[dik]

Just a caution... depending on the cracking it can be indicative of something going on... also, repairs can often make the cracking more noticeable.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[MRob909]

We tend to get involved in these types of repair in the UK quite regularly. As dik rightly highlights, the cause of cracking needs to be determined as the first priority. Our typical process is to determine if the cracking is:
- Historic (i.e. occurred when originally built) and not active.
- Historic but is active (i.e. cracks are progressing or getting larger).
- Recent and active/ not-active.

We will often undertake repeat surveys and deploy the use of crack monitoring gauges to record the cracks to determine active status. Alongside we will survey the building generally to try to determine the cause of cracking (ground heave, subsidence, settlement, drainage issues etc).

Regards to using Helibar, these are a very good product but only when used to repair a building that is not 'moving'. Note that if the original cause is not remediated and helibars are installed, you can actually cause additional cracking in new areas of the building as the stresses redistribute away from the repair zone.

When to use each type of repair (in my opinion) often comes down to:
a) Criticality of the masonry element. If just a partition wall then I would re-point. If load bearing and contributing to the structural load path or stability then I would helibar.
b) Size of crack. If cracking is small and not extending through the panel, then I would repoint. If cracking is significant then I would helibar.
c) Stability of the panel. Has the crack created a 'joint' in the panel and the stability has now changed? If yes, then I would helibar.

 

[StrEng007]

Thanks for that information.

That is another concern of mine... addressing the crack may introduce new cracks in the building as both of you have said. I mostly work with exposed/painted CMU or some sort of cementitious finish over the CMU. Very rarely is there a brick veneer. Is there a protocol you'd recommend for using a helibar at the location of the crack, then introducing a new vertical joint (offset by 24"?) with backer rod and sealant? The idea being to prevent the existing crack from getting worse and providing a new joint for extra measure incase the existing crack is active?

 

[dik]

Another caution... use proper mortar for repair, not Portland cement mortar... it's generally far too strong.

[URL unfurl="true"]https://res.cloudinary.com/engineering-com/image/upload/v1695733410/tips/Historic_Brickwork_23-02-05_qiuaph.pdf[/url]

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[StrEng007]

Anywhere I can find details for introducing a new control joint into an existing CMU wall that has a vertical crack? The vertical cracks I have completely vertically aligned and I can see these cracks have previously been sealed (likely) and painted over(definitely) in the past, and the crack occurred again at the same location.

The building is over 60 years old, and while I'm tempted to do the same thing as previous repairs (route, epoxy inject, paint), I expect the same issue will occur again. So if the building likes to crack at this location, why not put a permanent joint there?

I've also got the same issue with differential movement at the interface between block and a concrete tie-beam. It's a perfectly lined horizontal crack, and the CMU infill is for out-of-plan loading only (no in-plane shear).