brick wall cracks, your thoughts

[sybie99]

I am doing a report on a masonry building with significant cracking on walls.

In my view most cracking is as a result of foundation settlement. On one specific wall there is a continuous crack from top window corner to top window corner. I have read that this indicates settlement, what would be the reason for the crack forming at this location?

Other cracks in the structure are where joints have not been carried through continuously through the structure.

I attach some photos, I would appreciate your thoughts as my experience with masonry is limited.

Thanks

 

[hokie66]

Control joints in slabs not aligning with control joints in walls. Settlement, maybe, but not conclusive from the photos.

I don't see this in your photos, but where there is a continuous crack from top of window to top of window, corrosion of lintels is a common culprit. When steel corrodes, the ferrous oxides occupy a much larger space than the steel itself, thus creating expansive forces.

 

[sybie99]

Thanks Hokie,

Is south Africa we use pre stressed concrete lintels. There is a very definite crack along the full length (20-25m) from window to window, so you believe moisture could have penetrated through the mortar joint to the lintel causing corrosion?

 

[sybie99]

See attached photo of case where crack forms at bottom corner of window. This also occurs at many locations throughout the building. Another photo shows the cracks along the top of windows, in some instances the window has separated from the wall along the top of the window. What would this indicate.

If you look at the last picture, you can see the wall in question where cracks have formed from top of window to top of window, this is on the ground level. The wall has a balcony above so one would think it is well protected from the weather. Corrosion of lintels possible?

 

[Ironfrenzy]

It appears as if the cantilevered deck is creating a bending moment about lintel on the top of the window, thus resulting in a lateral cracking above and below the window.

 

[hokie66]

I was thinking of steel lintels in my first post. Not as likely with reinforced precast lintels. If that were it, you would see spalling on the lintel itself.

What is the material which frames the window openings? Hard plaster?

Another possibility is differential horizontal movement of the brick and concrete. Concrete shrinks, and brick expands with time. There don't appear to many control joints in the brickwork, and the ones that are there may not be working. Brick control joints, as opposed to those in concrete, must be full thickness in order to allow for expansion. I once saw brick control joints on a high rise building that, upon close examination, were just paint lines.

 

[Ron]

There appears to be some rotation associated with the balcony. The cracking dies out top and bottom and is more prominent near the balcony connection. Check the relative directions of faulting of the cracks.

Further, there is some deflection across the balcony joint, indicating probable water intrusion and deterioration with time. I would shore the area as deterioration does not follow a predictable timeless other than it gets bad very quickly in some instances.

 

[sybie99]

So your opinions do not include possible settlement of foundation?

For information, this specific wall is built about 1.5m behind a concrete retaining wall which creates an underground car park.

In other words, the footing of this wall sits on fill behind a retaining wall. I think I have just answered my own question! Could it be that the fill behind the wall was not properly compacted? It would make sense, as in all probability the remainder of the building is built on good in situ material, whilst this wall is built on compacted fill.