Concrete Shear Stress

Any ideas what may have cause this sheer right through the ledge of a garage window? No foundation cracks or any other sign of settlement.



I was looking at the joints and caulking around it and from what I can see there was no unevenness to them indicating previous movement. It is hard to tell from the picture but even the caulk immediately above the dropped section of ledge appears to be same width as to the left of it. The caulking also does not appear to be new.

What did it look like on the underside of the ledge? Was the mortar even across, new, old, looked repaired, missing, crumbled. Any signs of damage to the window, sashes, etc.? Is it possible it was cracked either during build, or possible rehab work, and never repaired, or so old a crack its cause is not discernible due to other potential changes (i.e. window repairs, mortar repairs, etc.)?

Thanks, Emmanuel. No I did not look under the broken slab. :neutral: It’s a 50 year old home. I’m just going to be honest and tell client I don’t know what caused the crack.

In any case, it’s cosmetic, not structural, in nature. It is curious that it can be dsiplaced vertically so noticeably, yet everything else around it seems to be in good condition. My guess is that it was indeed cracked during construction, and they just said “what the heck, it’s only a garage”, and left it that way.

I’m certainly not afraid to tell a client “I just don’t know”. I document what I find, provide potential causes during the briefing and call for further investigation if it warrants it. With what is shown there, and no other signs of movement or damage, I would recommend discussing the age and cause with the owner, sealing the crack to help prevent water and pest entry and monitor for future issues.

Pre-cast or natural stone ledges like this may suffer undetected natural fault or pre-installation stress fracture, the mortar bed deteriorates or freeze thaw cycles occur over time and voila the fracture appears.

A “good historic mason” can fix this fairly easily using the original materials so aesthetics aren’t lost.

Thanks guys for all the help. :cool:

The window unit (or actually original unit since it has been replaced) is bearing down on the hidden sill edge without good even support under the sill that rotated the sill to where part of the visible side (left) raised up. That age home has poor window headers that sag over time placing weight on the window unit. Still not a big concern. The crack was there when they replaced the window.