| Author |
Message |
Lynn Javoroski CSI CCS LEED AP SCIP Affiliate
Senior Member
Username: lynn_javoroski
Post Number: 437
Registered: 07-2002
| | Posted on Tuesday, October 24, 2006 - 02:36 pm: |    |
Situation: 3 coat exterior plaster system; seismic zone; 3/4 inch deflection/control joints both horizontally and vertically in a wall with moisture barrier, metal stud, "dens" type product sheathing.
Questions: How to terminate the plaster in an aesthetically pleasing manner with a finished edge at the joint AND what is the joint filled with?
Solution: Anyone have any? Plaster manufacturers are telling us that the largest "joint" they accomodate is 5/8 inch. |
Ronald L. Geren, RA, CSI, CCS, CCCA, MAI
Senior Member
Username: specman
Post Number: 348
Registered: 03-2003
| | Posted on Tuesday, October 24, 2006 - 02:49 pm: | |
Lynn:
Is the movement 3/4 inch, or is the width of the joint 3/4 inch?
If it's the latter, what is the movement? |
Lynn Javoroski CSI CCS LEED AP SCIP Affiliate
Senior Member
Username: lynn_javoroski
Post Number: 438
Registered: 07-2002
| | Posted on Tuesday, October 24, 2006 - 02:52 pm: | |
Ron,
I'm told that the maximum size of the opening is 3/4 inch and the minimum is 0. So the deflection is 3/4 inch? |
Ronald L. Geren, RA, CSI, CCS, CCCA, MAI
Senior Member
Username: specman
Post Number: 349
Registered: 03-2003
| | Posted on Tuesday, October 24, 2006 - 03:39 pm: | |
Hmmm...
Assuming that the original position is in a neutral location, the total joint movement would then be 3/4 inch: 3/8 inch in compression and 3/8 inch in tension. Therefore, you'll need a joint system that has about a 3/4-inch-width with 50% movement capability.
Is it possible to use 2 stucco casing beads with a 3/4-inch gap between the two, and fill the gap with a Class 50 silicone sealant? |
Wayne Yancey
Senior Member
Username: wyancey
Post Number: 196
Registered: 05-2005
| | Posted on Tuesday, October 24, 2006 - 05:16 pm: | |
Lynn,
I also suggest back-to-back square casing beads, 99% pure zinc.
I also suggest 7/8" thick 3-coat stucco. Stucco thickness will vary in the field. Stucco thickness is measured from the face of the WRB.
Put expansion control joints in the moisture barrier in same location as stucco expansion control joints. What is this product?
Metal lath is NOT continuous behind expansion control joints.
Ask for submittals for the stucco trim accessories to be sure the project will be getting the 7/8" deep type.
Also check out Fry Reglet, Gordon, and the vinyl cousins for the 99% pure zinc products. |
John Hunter
Senior Member
Username: johnhunter
Post Number: 12
Registered: 12-2005
| | Posted on Tuesday, October 24, 2006 - 06:16 pm: | |
We have a similar condition that we are working on. Superior has a double expansion screed that can allow for that amount of movement, and Fry has some standard 2-piece aluminum control screeds that can accommodate 3/8 inch of movement and we have talked to them about a custom fabrication for 3/4 inch. The recess could be painted and left exposed as a reveal. The advantage is that the joint will be covered and will not be reliant on sealant for the primary weather protection. Whether the aesthetics meet your requirements is, of course, a different matter. |
Phil Kabza
Senior Member
Username: phil_kabza
Post Number: 217
Registered: 12-2002
| | Posted on Tuesday, October 24, 2006 - 07:25 pm: | |
I would design with the expectation that the joint sealant would not survive a seismic event but is there to accomodate normal shrinkage and thermal movement in the surface skin. The larger joint is there to protect the more expensive elements in the assembly from seismic damage. If there's an earthquake, the failed sealant can be easily repaired, while the larger movement joints have accomodated the anticipated seismic movement and minimized fracturing of the finishes. |
Mark Gilligan SE, CSI
Senior Member
Username: markgilligan
Post Number: 106
Registered: 05-2005
| | Posted on Wednesday, October 25, 2006 - 12:33 pm: | |
Accepting damage in a major seismic event is typically acceptable. The problem is that you would not want significant damage in a minor to moderate earthquake or when subject to code wind loads.
My aproach to earthquake drift is to calculate the deflection under code earthquake loads prior to scaling up by R factors and use that as an estimate of drift under a moderate earthquake. Remember when dealing with earthquakes the forces in the building code are less than the forces that will occur in a major earthquake.
This is murky territory. There is no code guidance on this issue of servicability deflections, and if you want to get more refined numbers you can spend a lot of time studying the problem.
On the east coast where the earthquakes are not as frequent you may justify lower deflections prior to damage but when the moderate earthquake comes the building owner will probably not appreciate significant damage. |
Gerard Sanchis (Unregistered Guest)
Unregistered guest
| | Posted on Wednesday, October 25, 2006 - 02:47 pm: | |
Assuming that control joint spacing is 12 to 15 feet maximum, I doubt that sctuctural movement would be 3/4-inch between joints.
I would suggest that you verify those numbers. |
Lynn Javoroski CSI CCS LEED AP SCIP Affiliate
Senior Member
Username: lynn_javoroski
Post Number: 440
Registered: 07-2002
| | Posted on Wednesday, October 25, 2006 - 03:21 pm: | |
Gerard, the numbers have been verified; it's a seismic thing, evidently. Thanks.
John, Fry won't do anything but aluminum and we need zinc. Superior Metal Trim had exactly the extrusion we needed and in zinc.
Thank you all |
Wayne Yancey
Senior Member
Username: wyancey
Post Number: 198
Registered: 05-2005
| | Posted on Wednesday, October 25, 2006 - 03:48 pm: | |
Lynn,
This posting does not address your immediate concerns but is for your information and consideration.
It appears your stucco cladding is a face sealed system with no or limited redundancy. Although I do not know what region of the country your project(s) is located, consider the following for stucco cladding.
The following is a summary of an article by a former building science associate.
Drainage plane or no drainage plane behind stucco?
There is no right answer for this question because it is a matter of balancing risk with short and long term cost. Some points to consider:
Builders do not consider long term costs or long term risks so they will always favor the lowest cost option as long as it will not attract lawsuits.
Since stucco is porous, and always cracks, water will get through, and fairly quickly. The key issue is how the water that gets through is handled.
The key advantage of using strapping or a drainage material under stucco is that it provides a capillarity break as well as a drainage path.
Consider the thinking behind the new National Building Code of Canada requirements for high risk climates.
NBC requires that in climates like BC’s Lower Mainland, the “exterior walls exposed to precipitation shall be protected against precipitation ingress with an exterior cladding assembly consisting of a first plane of protection and a second plane of protection incorporating a capillary break”.
Proposed Sentence 9.27.2.2(1) states that “a cladding assembly is deemed to have a capillary break between the cladding and the back-up assembly where:
a) there is a clear air space not less than 3/8" (10 mm) in depth between the cladding and the inner boundary of the second plane of protection for the full height and width of the wall,
b) an open drainage material not less than 10mm thick and with a cross-sectional area that is not less than 80% open, is installed between the cladding and the back-up for the full height and width of the wall,
c) the cladding is loosely fastened to the backup and there is a clear air space behind each cladding component that is;
i) continuous for the full width of the component,
ii) not less than 3/8" (10 mm) in depth at the bottom of the component, and
iii) not less than 1/4" (6 mm) in depth over not less than 3.5" (90 mm) for every 9" (230 mm) of exposed height of the component, or
d) the wall is a masonry cavity wall or the cladding is masonry veneer constructed according to section 9.20.
Proposed Sentence 9.27.2.2(2) states that “the clear air space, drainage material and insulating sheathing described in Sentence (1) may be interrupted by
a) penetrations for windows, doors and services,
b) flashing,
c) masonry ties, and
d) furring provided the furring does not comprise more than 20% of the furred area.”
You may not be in a high risk area such the lower mainland of British Columbia and the Pacific Northwest, but redandancy in stucco cladding is something to consider. We in Seattle are also in seismic zone. We typically bump up the drainage cavity to 3/4" (19 mm) and use SBX treated strapping or steel Z-girt furring.
There is more to this topic but that is for another posting.
Wayne |
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