Cracked CMU Block Repair 2

[DWHA]

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.

 

[msquared48]

Looks wider at the top than aat the bottom unless the crack to the right of the door is part of the crack system too. Interesting that it happened over a door where the wall is weaker in bending from any settlement.

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

 

[BAretired]

I would consider epoxy fill in the cracks.

BA

 

[DWHA]

Yep, crack is wider at the top.

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.

 

[MiketheEngineer]

Someone makes a graphite (I think) material that is applied with an epoxy. Supposed to be stronger than the wall. Sorry I don't have better details

 

[Ron]

DWHA...don't rule out settlement. Wider at the top usually indicates that the ends have settled relative to the center. It only takes about a 1/4" of differential settlement in 20 feet to cause a crack. Considering the apparent width of the shown crack, it would only take about a 1/4" on each side to do that. Not much settlement, but the effect is a bit magnified at the top. If the crack were caused by shrinkage alone, it would go to one corner of the door or the other...not down the middle. Further, shrinkage cracks tend to break along mortar joints.

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)

 

[hokie66]

What will repair of these cracks achieve? If for aesthetics, the repairs will look as bad as the cracks themselves. Control joints are just straight, planned cracks, and maybe there weren't enough control joints. Repair or filling of the cracks won't accomplish anything structurally. If the walls are structurally adequate, why not just make the walls look better by concealing the cracking rather than repairing? Steel cladding is one way, which has the added advantage of making the wall watertight.

 

[BAretired]

The crack over the door gets wider toward the top, but the crack to the right of the door gets wider toward the bottom. Also, there are more cracks just above the door, so I'm not convinced that settlement is a factor.

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

 

[ToadJones]

Sika does make some amazingly flexible sealants. They cure like rubber and stay flexible virtually forever.

 

[a2mfk]

What part of the country (seismic, wind, both)?

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..

 

[DWHA]

A little info for all to help clarify the situation.

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.

 

[DWHA]

Here is another pic of that same corner with a crack right next to a control joint.

 

[frogit22]

presuming that the cause of the crack has been determined and rectified, it may be very simple to selectively remove the outer portion of the individual blocks that are cracked and replace with a 4" piece of block, set in mortar.

 

[frogit22]

if you think they are shrinkage cracks that may move, you may consider routing and sealing the cracks.

 

[hokie66]

Back to whether the wall is structurally adequate with or without the cracks. Is this wall reinforced at all? The appearance of the cracks would suggest not.

 

[DWHA]

I have not yet had a chance to determine the reinforcing of the blocks.

 

[hokie66]

Well, that would be my first step. No point in sealing cracks if the cracks indicate structural failure rather than just aesthetic nuisance.

 

[a2mfk]

I saw a step crack, I saw a step crack!! In the first picture.

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.

 

[msquared48]

It is very easy to determine the vertical reinforcing pattern with a hammer alone. The sound is very distinguishable as well as the feel. The size of the bar is another issue, and there are other means for this.

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

 

[BAretired]

Okay Mike, you are forgiven for disagreeing with me this time, but only this one time. From now on, you must tow the line and agree! agree! agree!...O.K.?

BA