Unusual stucco failure

This stucco separated from the wall forming a horizontal separation and crack near the top of the stemwall underneath this paito. Any ideas what could have caused it? My client asked me if it is indicative of a structural failure or simply a stucco failure. The flat roof above this area had a leak at the perimeter parapet wall that could have allowed water penetrat

ion to collect and freeze here. Suggestions are welcome.

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Improper installation… You don’t use chicken wire for stucco. Only stucco lath.


Good catch Roy.

Makes sense. Chicken wire is going to be tough to fasten and would make for poor adhesion to the stucco.

Roy’s right. Stucco lathe is to be used and the leak above didn’t help the issue, either. :roll_eyes:

Larry, Scott, and Roy
Thanks for the feedback. I listed improper installation referencing the stucco lath in the report.

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IMO, the ‘chicken wire’ is secondary to the cause. Likely the water intrusion at the parapet allowed moisture to travel along the WRB to the lower section of the wall, and without a proper weep screed system in place, it had nowhere to go except through the stucco!
(Note 2 inch minimum required above pavement)!



Thanks Jeffrey. There is no weep screed and the stucco is essentially sealed to the concrete slab.

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Although it’s nice to know why, keep in mind that it’s not incumbent on you to be able to articulate the specific mode of failure. Only that it has failed along with visible deficiencies in the installation.


No expansion joint material provided at the stucco/printed concrete slab intersection. This likely contributed to the failure.

Chicken wire bonded to felt paper commonly arrived as stacked panels (about 4’x12’) on the job in CA in the early 70s. Also common to first wrap the house in black felt, and then wrap the black felt in chicken wire. Millions of miles of these two components have been installed together in S. California. Most of it never pulled apart like that.
That looks to me like a shrinkage issue, failing first at a weak point… the stucco termination. I’m guessing it’s caused by the stucco materials not being up to parr.
Finally… nobody really knows without expert testing. No need to speculate in the report, but we’re always curious.


“Chicken wire” lath seems to be a regional thing. Around here it is the most common stucco lath. In general, diamond lath is superior. First, Chuck identified properly how to report it. Still, I agree that it is to our benefit to understand what causes bad things to happen. I think Jeffery’s explanation is a possibility when we have the information about roof and parapet leakage above. The way it buckled could be some movement from the patio slab. It looks like the slab was added after the wall was done. Shame on the contractor for pouring the slab on the wall like that…but we see that all the time.

Potential water intrusion might have affected any underlying framing. Since the loose stucco appears in the photo to bulge outward, this might be a symptom of compressive settling associated with deteriorating framing (if a framed structure).

Were you able to inspect any underlying rim joist? Was it CMU masonry or framed construction?

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Grant, I was not able to inspect the underlying rim joist. The attached photo shows the top of the wall under the porch covering. There is a flat roof over the house with parapet at the house wall and then another stepped down section of flat roof over the porch with another parapet around the perimeter. It is 100% frame construction.

Is it possible that this is a compression crack caused by heaving of the slab?


If this house is in a cold climate region, I would bet is largely due to melting snow from above (during the day), running down behind the stucco, accumulating below, then freezing and expanding at night.


Interesting thought, Joe. It does look like the right slab (my red annotations) is higher than the left slab.

Heavy, think clay, soils could push it up if it got saturated enough in that location somehow.


Steven, I think Joe and Larry’s idea about the adjacent slab affecting the stucco bears closer examination. Since the cracking runs along the full length of that slab area, and promptly ends at the corner (with the exception of minor relief cracking), a direct association could be deduced. Additionally, the corner close-up shows what seems to be slab up-lift of the area in question.

No expansion joint material lies between the slab and stucco which would break the bond between these materials. However, an expansion joint can be seen around the corner. Any slab lift affecting the attached slab would push directly against the stucco along its length.

Guys, thanks for all the great input on this topic. If I end up returning to this house I’ll be tempted to look more carefully at the slab to determine if it has up-lift. We can have significant snow load here and the parapet did have a leak (supports Steven’s hypothesis). It did not have expansion joints between wall and slab (supports Joe" hypothesis). The predominant soil in this region that the house is built on is very sandy (very little clay) and well drained and while it does freeze near the surface it usually thaws quickly and doesn’t go very deep. I annotated the lack of expansion joint on my report and recommended further review by a qualified professional.
Thanks again for all the input. I’ve learned a lot from the interaction.

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Being sandy soils with the additional influence of water saturating the area, could it actually be a problem of hydro consolidation?

Stephen, I’m with @jyoung32 and @lkage on this one. The crack appears to be caused by compression with the lath and top coat pushing away from the wall like that. My money is on the slab lifting, whether to from wet expansive soils or freezing water below the slab. Plus that crack is way too clean to indicate direct water damage. You nailed it with the lack of expansion joint. :+1: