Cracked CMU Block Repair
Cracked CMU Block Repair
(OP)
Does anyone know a good method to repair cracked masonary blocks. I have a situation where I have a block wall that has a almost completely vertical crack, crack goes through mortar joints and through the blocks themselves. The joints can be tuckpointed, but I am not sure the best approach to repairing the cracked concrete block itself. See attached picture.






RE: Cracked CMU Block Repair
I would suspect that this is a settlement crack and would look for another crack too. However, it could also be due to temperature - a shrinkage crack.
Best way I know is to seal the crack with a flexible mastic and monitor the crack for further movement to see if iti s due to settlement.
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Cracked CMU Block Repair
BA
RE: Cracked CMU Block Repair
I took a real close look at the area surrounding the crack. The foundation is in perfect shape. Also, there is no differential vertical movement between the blocks. So it is not a settlement crack. Definatly temperature. It is about half way between the control joints. So with the door there, it is the weakest section of wall to resist the cold weather shrinkage.
Unfortunatly there are cracks similar to this (not as large) all over the building. So it looks like there is some work that needs to be done.
RE: Cracked CMU Block Repair
RE: Cracked CMU Block Repair
For a permanent repair, break the outer shells, form and pour grout. Finish won't match so you'll have to stucco or texture coat the side.
Epoxies will work for the repair (Sika SikaDur 32 or similar), but masonry is a bit fickle on rigid repairs...expect another crack nearby. Mike's approach of sealant and monitoring is a good idea.
The carbon fiber approach mentioned by MikeTheEngineer can be done, it's just a bit expensive and the texture won't match either. Sika has a carbon fiber product as well. (Carbodur, I believe)
RE: Cracked CMU Block Repair
RE: Cracked CMU Block Repair
The only purpose in filling the crack would be for waterproofing, but hokie is quite right that a rainscreen would do a better job.
BA
RE: Cracked CMU Block Repair
RE: Cracked CMU Block Repair
Actually working on a CMU repair detail right now. And I look at cracks of various widths in CMU every week. They are one of the biggest judgment calls of any forensic engineer, whether or not the cracks are settlement or expansion/contraction related, or long term shrinkage, or a combination of several factors... And does the cracking require repair or is it "normal" settlement cracking, and of a small enough magnitude to not effect the strength.
I think everyone is bringing up good points, because the repair should be based on the cause of the distress and the intended end goal. I think a few overall pics and maybe a sketch that shows dimensions and openings would help everyone, especially in relation to expansion/contraction movements.
Do you know anything about the reinforcing or lack thereof?
I don't like the length, width, and location of those cracks. I am a bit conservative with CMU cracks greater than approximately 1/16", especially if this is a commercial building with walls well over 10ft. Openings already are weakened and have stress concentrations at the jambs. It also looks like there are cracks over the lintel, and that lintel looks like it was CIP with CMU, not a precast, which would make me suspect also.
If this wall is sparsely reinforced, then I'd add vertical bars in solid grouted cells to those jambs if they are not, and maybe adding a couple of horizontal bond beams to tie that crack above the door together may be prudent. I may also add another vertical bar and grout to the left of the downspout and have them sawcut an actual control/expansion joint (inside and out) and of course use a backer rod and elastomeric sealant.
Finally, with forensic and repair jobs, keep in mind that you are going on record with this problem, and I always figure I have bought that section of wall (or whatever it is you were looking at). Any further problems with that section of wall will be your problems too. The owner can always toss your letter or drawings in the garbage but that will be on them, not on you. Don't be afraid to be conservative in this instance with all of the unknowns..
RE: Cracked CMU Block Repair
I did a very close inspection of the foundaion (which is exposed about 2' above grade) and there is definately no differential settlement. The only cracks in the foundation are hairline. This is one of the best looking foundations I have seen.
The repair is to seal up the structure. It is in a location where no one will ever see the defect. The door shown is a back door that is never used.
Location is low seismic and normal design wind speed is 90mph.
Here is a pic of another crack location. This one is at a corner and the crack is right next to a control joint.
RE: Cracked CMU Block Repair
RE: Cracked CMU Block Repair
RE: Cracked CMU Block Repair
RE: Cracked CMU Block Repair
RE: Cracked CMU Block Repair
RE: Cracked CMU Block Repair
RE: Cracked CMU Block Repair
But I would agree the vertical cracks are from the lack of an expansion joint at the corner. The wall has formed the expansion joint for you, I would just make it official.
I think I would still strengthen the CMU around the door, the details depending on the location of grouted cells.
With all due respect, though you may be right about the settlement, I don't agree with this reason to conclude that:
"I did a very close inspection of the foundaion (which is exposed about 2' above grade) and there is definately no differential settlement. The only cracks in the foundation are hairline. This is one of the best looking foundations I have seen."
You said it was exposed to 2' above grade, so you have a reinforced concrete stem wall in addition to a strip footing? My point is that if you have a well-reinforced grade beam with a sparsely reinforced CMU wall on top of it, the foundation may show very little distress (cracks held tight as it deflects) while the relatively brittle CMU wall develops many cracks in it.
Just a theoretical point, it may not apply to your case.
RE: Cracked CMU Block Repair
The third photo with the stepped cracking seems to indicate settlement, but the fourth, with it's uniform cracking, shrinkage.
Be mindful, that this could be a combined issue here. However, until you can determine the cause and nature of the problem, I emphasize the need to temporarily seal the wall with a flexible mastic. To allow further water penetration will only further compromise the wall. Sorry BA, but I feel that a rigid seal is not the right thing to do at this time. Maybe later.
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Cracked CMU Block Repair
BA
RE: Cracked CMU Block Repair
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Cracked CMU Block Repair
Further photos imply other than settlement, but would be good to find actual cause. As Mike noted, water intrusion appears to be an issue, so seal it, even if it looks awful for a while.
RE: Cracked CMU Block Repair
RE: Cracked CMU Block Repair
That outta hold 'er!!
I wonder what that is about, and if it was built that way. That is not a continuous bond beam, that is just the lintel huh? Something like a mezzanine beam or joist girder in that area? If it was built that way, I guess local deflection of that lintel may be ruled out :)
RE: Cracked CMU Block Repair
Sorry I did not elaborate. It is a continuous bond beam around the entire structure. It is not just a lintel.
RE: Cracked CMU Block Repair
RE: Cracked CMU Block Repair
Did you verify IN THE FIELD that the bond beam is actually there? It may have been placed for a future mezzanine that was never built, or may have been eliminated if the mezzanine was eliminated.
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Cracked CMU Block Repair
RE: Cracked CMU Block Repair
The bottom course of the bond beam appears to be less than 8", so the beam height is probably closer to 22" than 24".
BA
RE: Cracked CMU Block Repair
As for the (8) #6 in the 24" bond beam, it is probably there considering the crack pattern seen at the doorway in your photos - they are much tighter together and spread out in the vicinity of the beam, which would be understandable.
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Cracked CMU Block Repair
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Cracked CMU Block Repair
What is happening is that the 24" deep bond beam is constraining the cracking just above the door jamb, making it appear that it is settlement related with the varying crack width.
The problem is temperature related, not settlement. I'm sure of that now.
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Cracked CMU Block Repair
RE: Cracked CMU Block Repair
If I was writing this up I would say that "Settlement is a potential contributing factor to the cracking observed in the CMU walls, but the main contributing cause is likely expansive/shrinkage movements within the CMU walls and a lack of properly placed expansion joints."
That'll be one beer if you use it, uhmmm, Hoegaarden will do.
And I would still do the other stuff I said above, call me conservative but I am not a fan of those cracks. And I'd add expansion joints and filled cells to each side of them, at least where the wall already cracked.
RE: Cracked CMU Block Repair
Settlement is not the only reason for stepped cracks. Diagonal cracking at ends of walls is also a typical type of restraint shrinkage cracking. The footing/stem wall restains the wall at its base, and the body of the wall shrinks up and away from the end.
RE: Cracked CMU Block Repair
Doesn't really change the outcome or repair recommendations, just trained now as a forensic engineer where you have to cover every base in your reports because of possible legal proceedings.
RE: Cracked CMU Block Repair
RE: Cracked CMU Block Repair
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask