by • June 10, 2014 • Exteriors - Siding, Stucco, Brick, Stone, Wood, Metal, Housewrap & Waterproofing, UncategorizedComments (8)24477

Massive Stucco Failure – Lessons Learned

I was driving by this restaurant remodel the other day and slammed on my brakes!

10 year old Restaurant with Stucco Facade

10 year old Restaurant with Stucco Facade

I made friends with the Project Manager and he allowed me full access to the site.  The first and most immediate failure you see is that the parapet walls & caps had huge failures.

Parapets were super rotted

Parapets were super rotted

I climbed up to the roof for a better look.  Luckily, the demo crew wasn’t quite finished so I got to see some of the layers behind the stucco. _MG_2495 The flat tops of the parapet walls had stucco on them.  Stucco is basically a porous cement product so any water that hits stucco will get through to the layers behind in no time.  These flat tops had 2 layers of tar paper behind them with little effort paid to sealing the joints and horizontal/vertical connections.  OUCH.

Tar Paper under the Stucco'd parapet cap.

Tar Paper under the Stucco’d parapet cap.

These rotted parapet caps present three lessons. #1  Don’t stucco over a Parapet Cap.  Stucco is porous and any water that sits on the stucco WILL get through.  Parapet caps should have some type of waterproof cap to prevent water from sitting on this horizontal area and leaking behind the WRB (weather resistive barrier). #2 If you MUST do a stucco cap then you’d better waterproof behind the stucco.  Tar paper is not a waterproofing product.  It does resist water, but it’s not waterproof.  It’s paper that’s been impregnated with tar.  Paper is not waterproof.  Tar impregnated paper is also not waterproof.

Transitions from wall to roof obviously were not dealt with properly.  Major rot here.

Transitions from wall to roof obviously were not dealt with properly. Major rot here.

Again a transition from roof to wall with no overhang that leaked big time.

Again a transition from roof to wall with no overhang that leaked big time.

The stucco was installed with the standard double tar paper method.

The stucco was installed with the standard double tar paper method.

Sprinkler that was wetting the building and caused huge failures.

Sprinkler that was wetting the building and caused huge failures.

This last photo above is particularly interesting.  You see that sprinkler head in the foreground?  That’s the only pipe or penetration I could find anywhere near this massive wall rot area.  There was no rot above 4′ so the leak wasn’t coming from above.  Remember that this building is only 10 years old.  I think this is a perfect example of why I think Tar paper is a terrible product to use for a WRB.  That sprinkler was wetting the wall 2-3x per week at 4Am and no one realized it.  The porous stucco soaked up the water, the tar paper got soaked and eventually the sheathing behind got wet.  There was no opportunity for this wall to do to the inside our outside with that volume of water. ( See this video I made about a stone veneer failure to learn more about Reservoir Claddings including Stucco and Vapor Drive. ) Lesson #3: Plywood rocks.  I realize these photos are pretty horrific, but if this sheathing would have been OSB I think this failure would have been even worse.  The plywood and 2x walls were able to soak up a ton of water and eventually rot happened.  However, if these leaks would have been smaller I think the real plywood and 2x’s would have been able to soak up the moisture and slow dry without incident.  Also, in all these photos I never saw any mold growth.  Mold loves the most broken down forms of wood.  Mold loves paper & OSB, but it has a harder time harnessing the food in solid lumber or plywood. Stay tuned for a post later this week on Stucco Best Practices and how you can prevent these failures.  I’m building a house right now with stucco parapet caps and I’ll show you the details to do this assembly the right way!


Matt Risinger – Risinger Homes in Austin, TX

Risinger Homes is a custom builder and whole house remodeling contractor that specializes in Architect driven and fine craftsmanship work. We utilize an in-house carpentry staff and the latest building science research to build dramatically more efficient, healthy and durable homes. Be sure to check out my video blog on YouTube, and follow me on Twitter @MattRisinger or visit my company Facebook page.

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  • rj

    Nice lessons learned post, particularly good as it addresses a common approach to building. Clearly any new buyer who reads this post will agree to upgrade the techniques. How was this flat roof done and how will you do the roof on your new job?

    • The flat roof was a torch down product and seemed to do fine. My typical flat roof is with Carlisle’s TPO membrane.

  • I would stay also away from stucco capped parapets in general, but we are adding onto a southwestern house and need to match the existing details. We are planning on a layer of ice and watershield on top of the framing and then lapping the rubber roof membrane over that. The stucco in this case will have an elastomeric coating which will help. In the past we have applied brush-grade Geocel sealant on the tops of stucco parapets. The Geocel or the elastomeric both need regular maintenance however; metal caps are much better if possible.

  • Great photos! I have quite a few similar ones. A member of one of my professional societies wrote a book of stucco wall cap flashing details. You may wish to see how it compares to your methods. I suspect that there will be a lot of similarities.

  • Stucco following ASTM C926 standards and ASTM C897 pay
    attention to the sand spec, will not leak. It will take on water but it will
    not pass through. Stucco is vapor permeable but water tight. This a very poor
    mix, utilizing a poor quality sand. The plasterers will complain that it does
    spread as easily without the clay but the cement based stucco will last
    forever. Leaks may occur at penetrations, terminations and openings, these
    areas do need to be flashed correctly directing water that does get behind the
    wall to the bottom.

    • Ron, Thanks for commenting! I generally operate under the assumption that any cladding will leak (eventually, or incrementally) so I’m advocating Best Practice Methods for WRB. This post shows the need for detailing behind Stucco. Stay tuned for my next Stucco post next week on my methods for Parapet Caps. Best, Matt

  • where the water gets in at and then how we manage that incidental water is what matters. if your interested send me your email address and I will send you a document that thoroughly explains stucco mix designs.

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