Hard coat stucco damage (C) InspectApedia 2017 Ron McClureHard-Coat Stucco Cracks, Leaks, Damage
Stucco cracks, leaks at control joints, standards

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Hard-coat traditional stucco inspection, troubleshooting, repair & standards.

Here, using a field report of leaks at horizontal control joints in a hard-coat stucco wall system, we describe the inspection, diagnosis, repair, and proper compared with improper installation of traditional stucco building wall surfacing systems. The discussion poses questions about the causes of leaks in stucco walls and also questions the reliability of stucco wall system standards.

Ron McClure discusses the hard coat stucco cracks, control joints, drainage, barriers and weep screeds.

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Hard Coat Stucco Cracking - a view from the field

Stucco wall exterior (C) Daniel Friedman

Ron McClure, January 2017

The Multicoat Hard Coat Stucco System is an Exterior Stucco System and is comprised of a weather-resistant barrier, lath, base coat, and a finish coat. The Multicoat Hard Coat Stucco System are applied directly to a structure at the construction site, or may be applied to prefabricated panels. - BuildSite,, from Multicoat Hard Coat Stucco System, cited at REFERENCES

OPINION: Information provided in this article comes solely from what I call "real world" conditions. These comments and opinions are the result of the inspection of thousands of stucco applications and they include only little consideration of building codes nor of ASTM standards for stucco installations. This is not because I believe in all cases these codes or standards are incorrect.

Rather, I find actual on-site field conditions give rise to a different point of view than what I see in building codes and standards The following opinion s are examples of my findings.

Stucco cracks are without a doubt the most asked about questions associated to stucco systems. Understanding that and without an in-depth study on the matter, the following information hopefully will answer your questions and give you information typically not provided in most home inspection reports.

[Click to enlarge any image]

Although cracks are the result of many different factors, some natural and some the result of construction or application errors, typically they are cosmetic only, common in hard coat stucco and not associated to damaging moisture infiltration. In some cases cracks can be of grave concern and need to be understood so that proper modifications and/or repairs can be made.

ASTM Standards for Stucco Systems

Unfortunately due to building codes that adopt ASTM (The American Society for Testing and Materials) standards there are some conditions associated to cracks that can be difficult to avoid.

Specifically, ASTM standards that relate to stucco systems, both ASTM C1063 & C926, do not appear to contemplate real world conditions and are therefore, in my opinion, incorrect and should not be used in the application of stucco systems. I believe through a better understanding of these problematic code requirements one can provide for better application and repairs details.

Opinion on Plaster Wall Drainage Systems

ASTM C926: Under A2. Design Conditions section A2.2 establishes design requirements for Drainage Behind Exterior Plaster. In this section it provides for the following requirement: "a drip screed and through-wall flashing or weep holes or other effective means to drain away any water that may get behind the plaster should be provided.”

The problem with this requirement is it suggest water will drain behind the stucco, a condition of which I have never seen.

In every case that I have found where water has entered behind the stucco, long before it ever gets (drains) to the base of the wall, the water has degraded the barrier and entered into the structure.

Plainly put there is no such thing as Drainage Behind Exterior Plaster and I do not believe anyone should ever consider it as part of a functional design element of a stucco system.

Opinion on Control Joints in Plaster Systems

Hard coat stucco control joint leaks (C) InspectApedia Ron McClure 2017

ASTM C1063: Installation of Lathing and Furring to Receive Interior and Exterior Portland Cement-Based Plaster section # defines the Standard for Installation of Control (expansion and contraction) Joints.

Looking at it from an engineering perspective, installation of control joints may sound quite logical, but my field examinations reveal that in the real world control joints do not eliminate field cracks. In fact, cracks at control joints are often the cause or source of very aggressive and damaging moisture infiltration.

One of the major problems I have with control joints like the one shown in the photograph here is that if the intent of a control joint is to serve as a design point for stress relief then doesn't it make since that relief would be in the control joint itself. If that is the case then the question begs to be asked:

Is a crack in a control joint better or worse than a crack in the stucco panel itself?

The answer is, it depends.

Due to the shape of the control joint, if a crack on a horizontal joint is on its upper side it normally would be of little concern (typical of general field cracks) although if the crack is on the lower side of the control joint it can result of excessive water infiltration.

The photograph above illustrates the stucco control joint and what appears to be a very small crack at the lower side of the joint. The clay mold in the photograph inset at upper right is used for the purpose of testing the crack for infiltration.

The two photographs below show the entry point of the water in this stucco covered wall.

Hard coat stucco damage (C) InspectApedia 2017 Ron McClure Hard coat stucco damage (C) InspectApedia 2017 Ron McClure

Note the following important findings:

  1. The point of water entry is the lower side of the control joint.
  2. Two layers of house wrap failed to keep water from entering into the structures substrate.

Editor's note: house wrap can prevent water intrusion if it is properly installed, lapped, taped, and sealed around openings and penetrations, but it will not prevent water intrusion if it is cut, torn, improperly placed, or left open around windows,doors, or other penetrations in the exterior walls. See Steve Bliss's comments on housewrap installation at HOUSEWRAP AIR & VAPOR BARRIERS

Moisture Damage from Leaks in Stucco Walls

Water damage in wall cavity where hard coat stucco exterior leaked (C) InspectApedia 2017 Ron McClure

This photograph shown the interior side of the same building wall wall with the drywall and insulation removed to show black stains, probably mold contamination from leaks into the wall cavity.

Although I do not believe the picture shown above of a horizontal control joint on the exterior of a building needs an explanation, the evidence given here demonstrates the potential problems associated with control joints: water infiltrating behind the stucco coating was not able to drain behind the stucco. [Instead it entered the wall cavity.]

In an attempt to determine the cause of some moisture related damage to some interior drywall we conducted some water tests at different points of the exterior wall and discovered the source of the water appeared to be at the control joints within the stucco system.

Cementious stucco hard coat wall leak evidence (C) Ron McClure

The photograph just above shows an area where the stucco was removed to expose the substructure and barrier.

Hard coat stucco damage (C) InspectApedia 2017 Ron McClure The photograph of a cut-out section of the hard-coat stucco wall coating shows the back side of a rectangular panel of stucco that we cut out of this leaky wall, including sections above and below the horizontal control joint.

The horizontal line dividing the 2 stucco panels is the horizontal control joint itself.

The panel is positioned as it was on the wall with the upper area of the cutout section being the upper portion of the panel when it was on the wall, and the lower area in the photo being the lower panel when it was on the wall.

The water-stained area on the back of this stucco cutout section was below the control joint.

Note the following:

  1. The upper panel has not been exposed to moisture related rust in the lath and staples.
  2. The lower panel, just below the control joint, has been exposed to moisture infiltration and related rust to both lath and staples.

Follow-up Questions about Leaks at Horizontal Control Joints in Hard-Coat Stucco Wall Systems

Editor's opinion:

McClure's photographs and comments illustrate serious leakage into a wood-framed wall structure. Leaks occurred from the building exterior, sending wind-driven rain or water run-down on the exterior wall through the horizontal control joint and into the building's wood-framed exterior wall cavity.

Leaks wet the interior side of the exterior wall sheathing, the building wall insulation, and probably the cavity-side of drywall on the wall interior surface. There may also have been an additional issue of mold contamination.

Since it's apparent that not all control joints in all stucco walls leak, some questions and their answers might help us understand this stucco leak failure more thoroughly.

The wall leaks described above might have occurred through a combination of physical causes, design questions, construction errors, and questionable building standards:

  1. Openings through the wall stucco coating at the horizontal control joint.

    A closer look, including close-up photos and photos of the wall cross section in a stereo microscope might give a better understanding of why the horizontal control joint leaked at this location and not at others.

    Were there failures in the sealant used in the control joint? Was it the proper sealant, properly applied on clean dry surfaces?

    Similar leak issues are discussed at SIDING EIFS WALL LEAK POINTS

  2. Absence of a functional drain system behind the hard-coat stucco that might have given an easy path for water to exit at the wall bottom or at a lower, flashed control joint as is used in some veneer systems with weep openings.

    Was this hard-coat stucco wall system designed with a purported drain system or was there none even attempted?

    What is the age of this leaky stucco wall?

    Where is this building located and in what climate?


  3. Defects in the building's house-wrap installed behind the stucco that let water penetrate the house wrap.

    What was the house-wrap material?

    Were there tears, cuts, or overlap-direction errors in the housewrap?

    Was the house wrap taped or sealed around windows and doors?

    Did leaks occur in those locations - perhaps at the horizontal joints over windows and doors or were leaks found only at the control joints in this stucco wall?


  4. Are some building standards unrealistic and do they serve more to protect manufacturers than consumers?

    If a building standard is so demanding that it is unlikely that contractors, in the field, will ever comply with all of of the standards provisions, and if compliance with the standard is absolutely essential for a successful product installation, does that tell us that the building system for which those standards were devised is a poor design that fails to recognize and accommodate "real world" construction situations, or are the standards reasonable and fall prey only to a minority of sloppy construction contractors?

    As ParexUSA notes:
    These requirements are essential to good practice. Failure to follow these requirements could lead to problems with the stucco assembly installation or ultimately, to its failure. Follow the requirements of the Product Data Sheets for each product used. - excerpted from "Stucco Appication Guide" by Parex at REFERENCES


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We are dedicated to making our information as accurate, complete, useful, and unbiased as possible: we very much welcome critique, questions, or content suggestions for our web articles. Working together and exchanging information makes us better informed than any individual can be working alone.


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Or see SIDING EIFS WALL LEAK POINTS for a photo guide to common leak points in synthetic stucco applications.

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