| Author |
Message |
Jerome J. Lazar, RA, CCS, CSI, SCIP
Senior Member
Username: lazarcitec
Post Number: 1165
Registered: 05-2003
| | Posted on Sunday, August 31, 2014 - 08:53 am: |    |
Direct Applied Stucco over CMU/concrete frame, no metal lath:
Building settles and moves which causes cracks which allows water to get behind the stucco. Then the stucco cracks and eventually spalls - major complaint from developers & owners. What could be revised in the specs to reduce this problem? Your thoughts? |
Dave Metzger
Senior Member
Username: davemetzger
Post Number: 530
Registered: 07-2001
| | Posted on Sunday, August 31, 2014 - 10:19 am: | |
On a project in the Middle East with exterior stucco over concrete and CMU, I specified Type 316 stainless steel lath (standard product made by AMICO).
Expensive?--yes. Likely to be accepted by Florida developers?--no. Will galvanized steel lath rust in the Florida climate (and Gulf climate)?--yes. Consequences of choosing not to pay up front for rust-resistant lath, when building settles and moves?--substrate cracks, water gets behind stucco, stucco cracks and eventually spalls. Will repairing the cracked concrete and CMU, and replacing the stucco, be more expensive than would using stainless steel mesh in the first place have been???
Any rigid finish which is bonded to a substrate will be susceptible to cracking of the substrate. What caused the building to settle to the extent that the CMU and concrete cracked?--inadequate compaction? earthquake? So how could the specs be revised to reduce this problem?--isolating the stucco from substrate movement is one way. How to achieve this isolation?--use of lath is an obvious solution. Are there other solutions?--I await those from other contributors to 4specs who have more experience than do I. |
Ronald L. Geren, FCSI, AIA, CCS, CCCA, SCIP
Senior Member
Username: specman
Post Number: 1255
Registered: 03-2003
| | Posted on Sunday, August 31, 2014 - 12:27 pm: | |
Design better foundations.
Ron Geren, FCSI, AIA, CCS, CCCA, SCIP
www.specsandcodes.com |
Dave Metzger
Senior Member
Username: davemetzger
Post Number: 531
Registered: 07-2001
| | Posted on Sunday, August 31, 2014 - 01:25 pm: | |
Of course, neither foundation design nor how stucco is detailed are specification issues (although they can be addressed in the specifications). These are design issues.
Revising the specifications will not prevent direct-applied stucco from cracking and spalling if the substrate cracks due to building movement/settlement. |
Mark Gilligan SE,
Senior Member
Username: mark_gilligan
Post Number: 683
Registered: 10-2007
| | Posted on Sunday, August 31, 2014 - 01:36 pm: | |
I basically agree with Ron although it could also be the result of failure to compact the earthwork.
If it is a design problem did the Owner contribute to the problem by hiring a cheap geotechnical engineer? Similarly was the structural engineer selected because he was passive and cheap?
Did the Owner hire inspectors to verify compliance with the design documents?
Often the Owner gets what he deserves although along the way it causes problems for the design professionals. |
Jerome J. Lazar, RA, CCS, CSI, SCIP
Senior Member
Username: lazarcitec
Post Number: 1166
Registered: 05-2003
| | Posted on Sunday, August 31, 2014 - 02:10 pm: | |
THE DEVELOPER IN QUESTION BUILDS 50 STORY PLUS CONDO BLDGS USING THE BEST ENGINEERS AND GEO TECH AVAILABLE...THESE ARE VERY HIGH END BUILDINGS ON AUGER PILE FOUNDATIONS ALONG THE OCEAN IN SOUTH FLORIDA. I AM TOLD ALL THAT CAN BE DONE TO ENSURE THE FOUNDATIONS ARE PROPERLY INSTALLED IS DONE.
ONE OF THE PROBLEMS MAY BE DUE TO THE STUCCO NOT BEING MOIST CURED AS PER CODE AND ASTM AS THE STUCCO IS INSTALLED. STUCCO SUBS CLAIM THAT DUE TO THE HIGH HUMIDITY THEY DON'T NEED TO MOIST CURE THE STUCCO. THIS IS ONE OF THOSE ITEMS FULLY COVERED IN THE SPECS, BUT IGNORED BY THE SUBS.
ALL THE OTHER POTENTIAL PROBLEMS ARE COVERED IN THE SPECS, SURFACE PREP, POLYMER ADDITIVES, MIXING, ACCESSORY USE, FIBER ADDED TO MIX, ETC.
STAINLESS STEEL LATH IS GOING TO BE A TOUGH SELL. EVEN WITH THE LATH IF THE BUILDING MOVES, THE STUCCO MOVES, IT WILL CRACK. |
Alan Mays, AIA
Senior Member
Username: amays
Post Number: 202
Registered: 02-2003
| | Posted on Sunday, August 31, 2014 - 05:04 pm: | |
Jerome, one must also understand that plaster is usually susceptible to cracking. Especially on high rise. That is why there are control joints. Bonded plaster usually doesn't allow for movement well.
The issue is, where is it cracking? Is it cracking at the head of the wall? Did they install deflection joints at the head of the CMU walls? Do the columns read through? Is there joints to allow for drift in the structure?
Finally Jerome, specs are not typically the problem. It is that designers and clients are trying to use plaster above the capabilities of the material due to the cost of the proper materials. Why is it that everyone goes to plaster as the cost solution? The best thing I ever heard a PM say to a client was that he should expect cracking. He explained that plaster is a worked material. He pointed out that you can even see where the scaffolding was due to the way the workers worked the plaster. In the morning they are flexible and bend over and work the full panel. Toward of the end of the day, they just don't bend over as much. Interestingly, I began looking harder and he was right. When they pull the scaffolding down you can see there the floor boards were. Also the wire tie spots. You see the patches.
Plaster is an imperfect material. expect imperfections with it. |
J. Peter Jordan
Senior Member
Username: jpjordan
Post Number: 761
Registered: 05-2004
| | Posted on Sunday, August 31, 2014 - 05:06 pm: | |
I would ask if the Contractor is allowed to not cure the concrete slabs because of the humidity. If the answer is that they must be cured, I would say the stucco must be cured.
A building this tall will probably move due to wind loading. I would ask if the cracks are more prevalent on the upper portion of the building or distributed throughout the different elevations.
Cracking in the stucco due to curing issues will probably show up earlier (within a few months) while it may take years for cracking due to various types of building movement to show up.
I would have to say that certain building practices in certain locations that have been generally accepted may not be correct. When I moved to Hawaii from the Mainland US, I tried to be particularly sensitive to the local construction practices, but in a few cases they were simply wrong. I finally developed the confidence to challenge these practices successfully.
In this particular case, a building practice that is widely accepted for one- and two-story buildings and has a long track record of success may not be appropriate for high rise construction. Ask the structural engineer how much drift or deflection he expects in the building. You may be surprised. Isolating the CMU from the structure may be required, and isolating the stucco from both the CMU and the building frame may also be required. "Honoring" the control and expansion joints is a must in the stucco application, and more control joints would probably help. This begins to make the weather barrier detailing (both at the design and construction phases) even more critical.
I just don't think you can take the way you design and build a two-story building and automatically apply it to a high rise. |
Mark Gilligan SE,
Senior Member
Username: mark_gilligan
Post Number: 684
Registered: 10-2007
| | Posted on Monday, September 01, 2014 - 01:58 am: | |
Given that the cracking in the plaster is apparently associated with cracking in the masonry I do not see how it is a stucco problem. You need to understand what causes the cracks in the masonry.
In a multi story building deflections in the slab could cause the cracking in the masonry especially if the masonry has minimal steel and if partially grouted. As suggested above the deflection due to wind could put forces in the masonry wall it was not designed for.
Is the cracking similar at all floors or does it just show up in the upper floors?
The fact that the subs did not implement the curing says a lot about how carefully they are complying with the requirements.
Unless the amount of cracking and/or the cost impact is small this has the potential to be a significant E&O claim. The best thing for the Architect and Engineer is to quickly investigate the problem bringing in experts as needed and develop a solution that can quickly be implemented. This has the best chance to reduce the potential repair costs and to minimize delays to the project which will reduce any potential liability to the design team. |
Phil Kabza
Senior Member
Username: phil_kabza
Post Number: 548
Registered: 12-2002
| | Posted on Saturday, September 06, 2014 - 12:34 pm: | |
Jerome: If our one-story stucco-on-reinforced CMU Florida house has stucco cracks, your high-rise condos certainly will. All 500 houses in our community develop movement cracks in the year following construction. A few problem houses have settlement cracks - distinguishable by their linear stair-stepping shape that follows the CMU joints. The more common stucco thermal movement cracks are more or less vertical and and irregular, and do not extend through the CMU. They are almost invisible on a hot sunny wall, and very obvious on a cool morning, indicating that they correspond to the walls' thermal expansion and contraction.
These are walls built to 140 mph wind design, with #4 vert @ 48 inch OC from foundation to continuous top-of-wall bond beam. The thermal cracks occur about every 8 feet.
The method of addressing the movement cracking here, which appears to be successful based upon 8 years' construction experience in the community, is to give the walls about two years after construction, then overlay the cracks with an elastomeric mastic patching compound textured and applied to match the knockdown stucco finish coat texture. Then repaint with a high quality high build paint with decent elongation properties. This results in a water-tight wall that after three or four years still appears to allow daily thermal movement without reopening of the cracks. The builders keep calling these settlement cracks, and don't seem to understand them. But the painters do.
On a high rise re-painting job where mobilization and labor are so expensive, I would emphasize careful preparation washing and look into using a stucco surface conditioner followed by a true elastomeric coating, possibly top-coated with a long duration paint with some sheen to enable self-cleaning or washing. That should be good for extended service. |
Jerome J. Lazar, RA, CCS, CSI, SCIP
Senior Member
Username: lazarcitec
Post Number: 1169
Registered: 05-2003
| | Posted on Saturday, September 06, 2014 - 06:03 pm: | |
I couldn't agree more Phil, in fact your line of thinking is right out of the book according to his highness Joseph Lstiburek (for Lstiburek fans). I always specify a 100% premium grade paint for the exterior walls over polymer modified fiber reinforced stucco (thank you Harry Rourke, RIP) applied to properly prepared substrates ( I hate bonding agents, but specify them anyway)...I recommend (but not include in the specs) that these same walls be repainted after min 2 years with a true elastomeric high-build coating - but this seldom happens and since I am not involved in post construction I am not able to confirm why. Lately we have been specifying an Acrylic high build coating like Thorocoat (rebranded to Masterprotect HB 400 - I hate BASF) over vertical stucco surfaces during construction.
The original question from the Developer (50+ story condo bldgs): is there any other solutions available? he agrees that settlement is inevitable in So FL and cracking will occur. Typically stucco is directly applied to CMU and CIP substrates, no lath, other than plastic lath at interfaces of different materials (ie at horiz joint between CMU and Concrete slabs).
The results of previous litigation reveals that improper application of bonding agents is a major instigator of stucco delamination in So FL. But there are so many other reasons. Contractors are lazy, they would much rather apply a bonding agent than rough concrete substrates to increase stucco bond (in fact the newest excuse is that roughening the concrete is increasing dust pollution). I am now specifying bonding agents with longer open work times, these are obviously more expensive and eventually get VE'd out of the job.
I've received valuable input from members of the Developer's post-construction team, I will post here shortly. I just finished issuing draft specs on another 50+ story condo bldg., so its been hectic. my apologies for not responding sooner to those on this board who have offered valuable comments regarding my queries. |
John Bunzick, CCS, CCCA, LEED AP
Senior Member
Username: bunzick
Post Number: 1589
Registered: 03-2002
| | Posted on Monday, September 08, 2014 - 10:32 am: | |
I would challenge the "high-humidity means no moist curing" assertion (though it may not end up being relevant to the problem you're solving.) The mass to surface area of stucco is much less than concrete, and it is completely exposed to the wind. That has to lead to very rapid drying. |
David G. Axt, CCS, CSI ,SCIP
Senior Member
Username: david_axt
Post Number: 1374
Registered: 03-2002
| | Posted on Monday, September 08, 2014 - 08:12 pm: | |
Stucco cracks!
I recommend lots of control joints and a good elastomeric paint or coating applied over the top.
If you really want to have the definitive reference on stucco, buy this book from the Northwest Wall and Ceiling Bureau.
https://www.nwcb.org/content/stucco-guide
David G. Axt, CCS, CSI, SCIP
Specifications Consultant/Web Publisher
www.localproductreps.com |
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